The disclosure relates to shaped ophthalmic lenses and methods for providing such lenses, including non-powered lenses having non-quadratic surfaces of complementary curvature. Such lenses may have a curvature maximum away from an axis of symmetry and a substantially constant wall thickness. Equations describing and methods of designing such lenses are disclosed including embodiments where two spheres of substantially different curvature are merged in accordance with a weighting function, and adjusted using merit functions.

It is known in the prior art to manufacture non-corrective eyeglasses such as sunglasses or protective eyeglasses having wrap-around segments designed to shield the eye from incident light, wind, and foreign objects in the temporal vision field of the wearer. Such plano eyewear may curve horizontally around the eye sockets to "wrap" around and enclose the eyes as far as 100° from the line of sight. Vertical contouring of inferior regions of the lens inward toward the cheeks is variously called "pantoscopic tilt" or "rake", depending how the effect is achieved. The lenses may be designed to fit into dual lens frames or they may be of the unitary shield type. Wrap and/or rake create aesthetically pleasing eyewear that provides wearer comfort, but introduce also optical distortions that present difficulties to wearers involved in precise visual tasks. Various surface forms and arrangements have been employed in order to improve the closeness of wrap and rake provided. Whilst some of these arrangements have allowed faithful imaging at a wearer's direct line of sight for distant vision, inherent oblique refractive errors are introduced by lack of spatial correspondence between the lens optical axis and the direct line of sight as worn. Some prior art of the early 20th century employed spherical and elliptical dual lens designs of approximately constant thickness, thus not having an optical axis, but these have negative power and exhibit substantial refractive and prismatic distortion whenever the curvature center does not fall on the direct line of sight. To achieve functionality for dual lens eyewear, this type of lens needs to have exceptionally high base curve (˜16 to 21D) so that it may be positioned approximately concentric with movement of the wearer's eyes. Alternatively, a unitary lens should be of such low base curve that the offset distance between the direct line of sight of one eye and the optical axis located within the wearer's medial plane is very much less than the vertex radius of curvature, being say in the range 1 to 2D. The vast majority of eyewear utilizes base curves intermediate between these conditions.
Prior art cited by Rayton 75 years ago (U.S. Pat. No. 1,741,536) attempted to achieve the effect of wrap and/or rake by tilting nominally zero power lenses outward and/or downward and aligning the optical center of the lens with the wearer's direct line of sight. The method was rejected owing to the existence of prismatic distortion in the as worn position. More recent art teaches a method of overcoming such prismatic error for pairs of low minus lenses. Reichow and Citek disclose in their U.S. Pat. No. 6,129,435 the achievement of the appearance of wrap and/or rake by inward and/or upward displacement of the geometric center of the lens, the induced-prismatic-error as worn being corrected without change in the physical appearance of the lens by rotating it about the center of curvature of its front surface to dispose the optical axis inward and/or upward. There remains, however, a negative mean power at the direct line of sight. It can be demonstrated that an opposed set of rotations would correct the prismatic error as worn for pairs of low plus lenses. However, the vast majority of non-corrective eyewear setup is based on Prentice's Rule (1888), an approximate analysis that predicts a linear relationship between the optical prism at a line of sight decentered with respect to a lens and the back vertex power of that lens. Most commonly, lenses are designed to provide zero back vertex power. Their optical axes and the wearer's direct lines of sight, as worn, are displaced laterally from each other as desired, while maintaining parallelism between them. This arrangement is shown in FIG. 1A; the line 2–2′ is the direct line of sight and 1–1′ is the displaced optical axis.
Rayton in U.S. Pat. No. 1,741,536 and Jannard in U.S. Pat. Nos. 4,674,851 and 4,859,048 disclose cylindrical lenses. Jannard (U.S. Pat. No. 4,867,550) and Burns (U.S. Pat. No. 4,741,611) describe toroidal lenses. Montesi and King (U.S. Pat. No. 4,271,538) and Conway (U.S. Pat. No. 5,555,038) describe unitary eyewear with left and right spherical lens portions whose optical axes are displaced nasally from the direct lines of sight as worn. Houston et al. (U.S. Pat. Nos. 5,648,832 5,689,323 and 6,010,218) describe spherical lenses that are decentered with respect to the direct line of sight in both a horizontal and a vertical plane. Fecteau et al. (U.S. Pat. Nos. 5,825,455, 6,019,469 and 6,254,236) describe unitary lenses having surfaces formed by rotation of an ellipse, parabola or hyperbola around a horizontal axis located rearward of the wearer's eyes. Davis and Waido (U.S. Pat. No. 5,604,547) describe unitary lenses whose surfaces are paraboloids that are bent in the lateral regions to form a side wrap beyond the wearer's visual fixation. They describe also unitary style sunglasses or eye protectors having a lens with inner and outer surfaces that are oblate ellipsoids. The surfaces they discuss also have a region of maximum surface astigmatism on the lens surface. Tackles (U.S. Pat. No. 5,774,201) describes both unitary and dual lens styles wherein the horizontal arc of a lens cross-section has a medial portion and lateral ends, the lateral ends having gradually tightening curvature relative to the curvature of the medial portion in substantial conformation to a portion of an ellipse with eccentricity in the range 0.1 to 0.85. The vertical curvature may take any desired form.
In order that a spherical lens can have zero back vertex power, its front and back radii R1 and R2 are related by R1−R2=t(n−1)/n where t is the lens center thickness and n is the material refractive index. This stipulates that the caliper thickness of the lens (measured normal to either surface) will have a maximum value at the lens center and taper everywhere away from the optical axis of the lens, a matter long known in ophthalmic optics. For example, Rayton describes lenses with wall thickness tapering away from the optical axis. Conway notes that a lens which tapers continuously outwardly from its point of maximum thickness (optical center) has constantly zero power and low prismatic imbalance at an eye sweep angle of 20° whereas a similar lens of constant wall thickness has negative power and relatively higher prism imbalance. Others, including Montesi, Jannard, Tackles and Houston et al., make claims directed specifically to non-corrective lenses characterized by tapering thickness.
In an apparently contrary viewpoint, Davis and Waido claim non-corrective unitary lenses having "substantially uniform thickness throughout". Their stated development objective was to "provide improved sunglasses and safety eyewear with relatively uniform thickness throughout without sacrificing optical performance". Specifically, the design task was to correct unwanted thinning of the lens in the region of the lateral bend and avoid any requirement to manufacture unnecessarily heavy lenses. Each of those designs disclosed in U.S. Pat. No. 5,604,547 have been analyzed and have found the corresponding lenses to have thickness that tapers from the optical center across the field of view to the lateral bend, in which region there is localized thickening of the lens wall. In the same region, there are consequent negative refractive errors. Accordingly, this disclosure does not contradict prior wisdom.
The design of non-corrective lenses has been simplified greatly by concentration of the industry on the quality of distant vision in forward gaze. Optical testing is typically undertaken using a telescope aligned with the geometric axes to evaluate the optics at the direct lines of sight as worn. Oblique refractive errors, very important to ophthalmic lens design, are frequently ignored in the analysis of non-corrective lenses. Industry standards typically quote tolerances for refractive and prismatic errors at the "as worn" position only. See Table 1 below.
TABLE 1Some specifications for refractive and prismatic errors of non-correctivelenses at the direct lines of sight, as worn.At Line of SightLeft/Right Imbalances at Lines of SightStandardPowerAstig.PowerAstig.Prism Prism ANSI Z80.3-1979+0.12/−0.250.180.180.180.4750.475 outANSI Z87.1-1979±0.060.120.060.120.1250.125 out, 0.52 inISO TC94/SC6 Gr. 1±0.060.120.060.120.12 1.00 out, 0.25 inISO TC94/SC6 Gr. 2±0.120.250.120.250.25 1.00 out, 0.25 inCEN 1836±0.090.090.180.180.24 0.24
Depending on the base curve, material and lens center thickness, these tolerances allow significantly different lens characteristics in the oblique visual field. The arrangements and devices of the prior art described above all result in the optical axis of a lens being placed somewhere in space other than coincident with the direct line of sight. The two vectors may intersect in some plane, they may be strictly parallel, or they may be skew. All such arrangements result in image aberrations for a simple object field that are asymmetric with respect to monocular rotation, which effect increases the magnitude of oblique errors experienced. It also causes a wearer's left and right eyes to experience mirrored image aberration fields, introducing binocular disparity for version movements. These being the primary optical demand in distance vision, the disparity is a distinct disadvantage of current designs. Ophthalmic lenses, on the other hand, are presented by convention in front of the eyes so that the optical axes and direct lines of sight are closely identical. The oblique fields are designed to be substantially symmetric with respect to monocular rotation and substantially free of binocular disparity in version and vergence movement, unless required by prescription.
Accordingly, it would be highly desirable to devise methods and means by which to place non-corrective lenses of aesthetically pleasing and useful shape before a wearer in a face-fitting configuration so that: the optical axes of the lenses and the wearer's direct lines of sight are substantially aligned, or; the visual fields are symmetric with respect to monocular rotation, preferably; both. Given the extent of prior art in this field, it should be expected that lenses meeting our objective could exhibit unusual physical characteristics, particularly in the conformation of their surfaces. Perspective views of a pair of lenses of an embodiment of the present invention are shown in FIGS. 2A–2D.
Reshef et al. have described very highly curved non-corrective goggle lenses with a spherical surface (radii below 35 mm) and having tapering thickness (U.S. Pat. No. 5,094,520). Applicant has developed also novel prescription lenses, sunlenses and eyewear characterized by steeply curved surfaces (˜16 to 18D) that are approximately spherical and are placed concentric with the centroid of rotation of the eye. These objects are described in detail in Sola International's U.S. Pat. No. 6,142,624, the entire disclosure of which is hereby incorporated by reference. Lenses of this type deviate substantially from conventional, relatively flat lens shapes. However, the overall shape of such lenses is based on generally spherical reference surfaces employed and their optical properties in the oblique field can be sensitive to lens placement errors.
Sola International has developed improved aspheric prescription lenses for use in wrap-around frames, as described in their U.S. Pat. No. 6,361,166 the entire disclosure of which is hereby incorporated by reference. Sola International has developed other novel optical lenses suitable for use in wrap-around or protective eyewear. These lenses are described in U.S. Pat. Nos. 6,334,681 and 6,454,408 to Sola International, the entire disclosures of which are hereby incorporated by reference. These applications describe close fitting prescription shields, visors or dual lens prescription sunglasses whose physical form is achieved by forcing local change in curvature of the Rx lenses, particularly in the forward visual field of the wearer, in order to depart significantly from conventional (quadratic) conicoidal forms and by employing significant shape asymmetry between horizontal and vertical meridians of the lenses. However, these surface forms lack overall global definition, introducing difficulty in optimizing lens appearance and wide-field visual function from the wearer's viewpoint. The lens surface construction is mathematically complex, even for lenses having a simple axial symmetry. Also, the oblique optical errors formed at the limits of a wearer's visual fixation field may be less desirable than those of more classical construction based on standard optical surfaces of quadratic form with or without surface aspheric corrections.
Terminology
There are several technical terms and descriptors used within the following discussion of the present invention that either have specific meaning herein, or that are unfamiliar terms within the field of non-corrective lens design. In the interests of clarity and understanding, we list those terms and their meanings as used herein below. Mathematical terms and meanings follow those found in CRC Concise Encyclopedia of Mathematics, by E. W. Weisstein, Chapman & Hall, New York 1999. Optical terms and principles follow those to found in Optical Society of America Handbook of Optics, Volume I, Part 1, M. Bass (Ed), Second Edition, McGraw Hill, New York 1995 or in The Principles of Ophthalmic Lenses, M. Jalie, Fourth Edition, London 1994.
The term "optical lens element" means, in this application where appropriate in the context of particular embodiments, a finished optical or spectacle lens, a lens blank that requires cutting edging and fitting to a frame assembly, or a light transmitting article formed so as to provide a left and a right lens and being suited to finishing as an integral optical element or shield for non-corrective eyewear.
The term "monocular field of view" means, in this application where appropriate in the context of particular embodiments, a portion of solid angle before a wearer in which the human eye is able to receive and distinguish images. It is generally considered to extend approximately 90° temporally, and up to 60° nasally, 70° inferiorly and 50° superiorly, depending on an individual's facial structure, the illuminance and the stimulus size, duration and color.
The term "binocular field of view" means, in this application where appropriate in the context of particular embodiments, the overlapping region of left and right monocular fields of view, divided centrally by the wearer's medial plane.
The term "version movement" means, in this application where appropriate in the context of particular embodiments, binocular pursuits within an object plane wherein both eyes move equally in the same direction.
The term "vergence movement" means, in this application where appropriate in the context of particular embodiments, binocular pursuits at different distances from the observer wherein both eyes move equally in opposite directions.
The term "visual fixation field" means, in this application where appropriate in the context of particular embodiments, a region on the lens surface defined by a set of points that are the intersection of the lens surface and the wearer's line of sight as he or she fixates on objects in a median plane. This visual field is typically associated with ocular rotations in the order 40 to 50°.
The term "peripheral field of vision" means, in this application where appropriate in the context of particular embodiments, a region on the lens surface defined by a set of points which are the intersection of the lens surface and rays of light entering the wearer's pupil as he or she fixates on objects generally in the direct line of sight. The eyes are typically static, exhibiting only small ocular rotations.
The term "quadratic standard forms" means, in this application where appropriate in the context of particular embodiments, a surface belonging to any of the 17 general standard-form quadratic surfaces and special cases thereof as set forth in the CRC Concise Encyclopedia of Mathematics, by E. W. Weisstein, Chapman & Hall, New York 1999, p. 1485.
The term "standard optical surfaces of quadratic form" means, in this application where appropriate in the context of particular embodiments, any biconvex or plano-convex surface being a section of a cone, cylinder, sphere, spheroid or conicoid belonging to the generic families of ellipsoids or of toroids formed by the rotation of generally conic arcs around an axis that is a surface normal or is parallel to and spaced from a surface tangent. The surface form will be continuous at least to the third derivative and have discernable symmetry with respect to at least one reference normal vector.
The term "axis of symmetry" means, in this application where appropriate in the context of particular embodiments, the normal vector relative to which the surface sheet has at least reflection symmetry and on which the centers of sagittal curvature of individual surface elements are located.
The term "vertex" means, in this application where appropriate in the context of particular embodiments, the point of intersection of a surface and its axis of symmetry. By the term "apex", we mean the forward-most point on a lens surface as worn.
The term "optical axis" means, in this application where appropriate in the context of particular embodiments, the axis on which the sagittal curvature centers of both surfaces is located. It is formed when the axes of symmetry are collinear. The surface sheet is usually defined in cylindrical polar coordinates (r, □, z) where the origin of coordinates is the surface vertex, the optical axis is the axis Oz and the radial distance r is measured within the surface tangential plane through the surface vertex, the "vertex plane". The directed distance z(r) from the vertex plane to the surface is known as the surface "sag". Preferably lenses according to the invention are located before a wearer so that the optical axis of the lens and the wearer's direct line of sight in distance vision are essentially coincident.
The term "optical center" means, in this application where appropriate in the context of particular embodiments, the point where the optical axis intersects the lens front surface. It may be determined in practice as a location where the lens has zero optical prism, while the orientation of the optical axis may be found by identifying the normal vector to a surface tangential plane at that location.
The term "sagittal curvature center" means, in this application where appropriate in the context of particular embodiments, the center of rotational curvature defined by the surface slope in any meridian. It is located to the concave side of the surface at a distance from the vertex given by
  R  =            z      +                        r                      z            ′                                                                    where                                                            z          ′                      ≡                  ∂        z                    ∂        r
The term "standard optical reference surface" means, in this application where appropriate in the context of particular embodiments, a quadratic surface, including aspheric correction terms if any, such a surface being characterized by tangential and sagittal surface curvatures changing monotonically without local maxima or minima away from the axis of symmetry.
The term "significant deviation from standard optical reference surface" means, in this application where appropriate in the context of particular embodiments, a surface having quadratic and higher order components, including aspheric correction terms if any, the overall surface being characterized in that at least the tangential curvature or mean curvature exhibits a maximum value at an oblique position along at least one meridian.
The term "significant deviation in surface curvature from a standard optical surface of quadratic form" means, in this application where appropriate in the context of particular embodiments, that the tangential and/or sagittal curvatures of individual surface elements show at first increasing difference for elements away from the axis of symmetry, and thereafter a declining difference more distant from the axis of symmetry.
The term "significant deviation in surface astigmatism from a standard optical surface" means, in this application where appropriate in the context of particular embodiments, that the tangential and sagittal surface curvatures deviate sufficiently to introduce major optical astigmatic distortions to the lens surface.
The term "static prism" means, in this application where appropriate in the context of particular embodiments, the component of prism that is perceived when sampling rays that enter the wearer's pupil as he or she fixates on objects in the straight ahead viewing position and where the eye is static. This prism is typically associated with peripheral visual perception.
The term "rotational prism" means, in this application where appropriate in the context of particular embodiments, the component of prism that is perceived when sampling rays along the wearer's line of sight as he or she rotates the eye. This prism is typically related to ocular rotations in the order 40 to 50 degrees.
The term "sagittal depth" means, in this application where appropriate in the context of particular embodiments, the distance between the surface tangential plane at the front vertex of the lens and the temporal-most edge point of the front surface. By the term "difference in sagittal depth", we mean the difference between the sagittal depths at the temporal-most edge point of the front surface and at the nasal-most edge point of the front surface.
"Mean Through Power" is the average of the through power in one principal meridian along a given line of sight and the through power in the other principal meridian along that line of sight. "Mean Power Error" (MPE) is the arithmetic mean value of the actual errors in lens through powers in the principal meridians along a given line of sight, compared with the desired refractive correction. "RMS Power Error" (RMSPE) is the root mean squared error of actual lens through powers in the principal meridians along a given line of sight, compared with the desired refractive corrections. The term "substantially zero mean through power" means, in this application where appropriate in the context of particular embodiments, that the mean through power is in the range −0.50D to +0.125D, preferably −0.30D to +0.05D, more preferably within ±0.09D, most preferably within ±0.05D in the visual fixation field of the wearer.
The term "surface Q-value" means, in this application where appropriate in the context of particular embodiments, a measure of the degree to which a curve or a surface may be described as quadratic. It is determined for a curve from the first and second derivatives along the curve length. For a surface, it is determined from the tangential and sagittal curvatures or radii of curvature.
The terms "eccentricity" and "shape factor" mean, in this application where appropriate in the context of particular embodiments, the standard measures of the degree of departure of a conic section from a perfect circular section.
The term "surface curve" in accordance with a preferred embodiment of the present invention means, in this application where appropriate in the context of particular embodiments, a planar curve that has; an axis of symmetry; relatively low curvature at the central portion and relatively higher curvature at the lateral ends; a local maximum of curvature at an intermediate position between the central portion and the lateral ends, and is further characterized in that the normal vectors to the curve at its opposed regions of greatest tangential curvature are inclined angularly with respect to each other.
The term "osculating surfaces" means, in this application where appropriate in the context of particular embodiments, a pair of surfaces that are co-tangential with each other at a closed curve of intersection between them. The surfaces have equal sagittal curvature at their intersection.

Shaped non-corrective eyewear lenses and methods for providing same


In a wire bonding apparatus and method which reduces variances of the length of tails of bonding wires without increasing the total wire cutting time, a capillary and a wire cutting clamp are moved up fast 10 and then slowly 11, after the wire is bonded to a second bonding point 1, to a-point slightly below a desired tail length S, and then the capillary and the clamp are moved up slowly 12 so that the clamp is closed to cut the wire and then moved up fast 13 and slowly 14 again.

1. Field of the Invention
The present invention relates to a wire bonding method and apparatus and more specifically to a method and apparatus for cutting a wire after a bonding is performed to a second bonding point.
2. Prior Art
FIG. 6 shows conventional wire bonding actions.
A capillary 3 and a wire cutting clamp 4 are moved up as shown in FIGS. 6(b) and 6(c) after a bonding wire 2 is bonded to a second bonding point 1 as shown in FIG. 6(a). In this case, the speed of the capillary 3 and wire cutting clamp 4 moving up is, as shown in FIG. 5(b), first increased as referred to by numeral 5 and then decreased as referred to by numeral 6.
While the moving up speed of the capillary 3 and wire cutting clamp 4 is accelerated at 5, the wire cutting clamp 4 is closed, thus cutting the wire from the attachment base of the second bonding point 1 as shown in FIG. 6(c). As a result of this cutting action, a certain length of wire (called the "tail" of wire) 2a is left below the tip of the capillary 3 so that a ball is formed at the end of the tail 2a in the next step.
The length of the tail 2a often affects the size and quality of the ball; accordingly, the tail length is extremely important in wire bonding. A wire cutting method of this type is described in Japanese Patent Application Publication ("Kokoku") No. 62-52948.
In this prior art, the wire cutting clamp 4 is moved up very fast while it cuts the wire. As a result, the timing of cutting the wires differs as shown by T1 in which the wire cutting clamp 4 is closed, and such a difference T1 causes a variance of S1 in the length S of the tail 2a as shown in FIGS. 5(a) and 5(c). Thus, tails of equal length are not always obtained. This variance in the tail length can be reduced if the moving speed at acceleration 5 is slowed down; however, this results in a long total wire cutting time.


A fraud monitor in a managed network is provided. The fraud monitor uses the network's instrumentation data, configuration data, and account information to detect fraudulent activities in the network, such as fraudulent advertisement or other types of fraudulent data traffic, including fraudulent responses (e.g., fraudulent clicks) to advertisement. The fraud monitor receives configuration data and identification data for physical resources of the network. The fraud monitor receives instrumentation data of packet traffic in the network. The fraud monitor receives account information for users of the network. The fraud monitor analyzes the instrumentation data to detect a violation of a fraud detection policy that prevents malicious or fraudulent online advertisement activity based on the configuration data, identification data, or account information.

Fraud conducted over the Web or Internet is a rampant problem hurting individual users as well as businesses. Legitimate websites are often populated with fraudulent advertisement that aims to solicit clicks for providers of malicious content. Fraudulent actors may also hire click farms to automate inputs to appear to "visit" websites in order to inflate click statistics and defraud website operators, advertisers, or online advertisement exchanges. These forms of fraud can be difficult for individual users and businesses to detect, since a visitor of a website or an online advertiser are unlikely to have all the information necessary to identify fraudulent content or fraudulent clicks.


A mobile phone provided with lighting devices capable of capturing not only a still image but also a moving image in the dark. When a user sets the lighting of a light emitting section to ON at the time of capturing an image, the light emitting section is controlled so as to illuminate a subject for the most suitable time for capturing the image regardless of capturing a still image or moving image. Accordingly, it becomes possible to capture an image in the dark successfully. Moreover, the mobile phone can be used as a flashlight by continuously turning on the light emitting section that would be used when capturing an image. Accordingly, the mobile phone may be used for lighting when finding a keyhole, searching for something, etc. in the dark.

The present invention relates to a mobile phone provided with lighting and an image capturing device for transmitting image information such as a self-portrait to a receiving end, a method and a program thereof, and in particular, to a mobile phone provided with lighting having a lighting function to illuminate a subject when capturing images, a lighting control method and a program thereof.

Mobile phone provided with lighting, lighting control method and lighting control program


In a process and unit for gradual decoding, archiving and graphic display of progressively decoded image data, time intervals between the time points of consecutive decoding steps, during which network users receive ever more refined image resolution when downloading image data from a central network server to the client computer using transferred and decoded partial data quantities ΔLi as preview images, are generated with abbreviated time spans that are optimized with respect to minimization of system usage by the decoding system. For this purpose, the receiving data rates for transfer of the individual partial data quantities, which are taken into account through improvements generated by the individual decoding steps of a quality metric showing the degree of image resolution and the temporary usage of the decoding system upon determination of the decoding time points. The wait times between the time points of directly consecutive decoding steps are calculated using statistical image quality parameters of received partial image data in such a manner that the decoding steps which do not lead to a perceptible improvement in the quality of a reconstructed image are suppressed.

1. Field of the Invention
The present invention concerns a process and a unit for gradual processing and, when necessary, graphic display of progressively coded image data, which help to shorten and, with respect to minimization of system usage, optimize the time span during which network users are provided progressively refined image resolution when gradually downloading image data from a central network server to their local client computers in the form of transferred and decoded partial data quantities as preview images, for example.
2. Description of the Prior Art
The following provides a brief presentation of the principle of progressive image coding as applied within the framework of the Progressive JPEG Standard. Because the solution that forms the basis of the invention is, however, independent of the actual image coding standard and only one progressive process is assumed, other standards, e.g. JPEG 2000 or Interlaced GIF, can be used besides the Progressive JPEG Standard described here.
The file format that has come to be known as "Progressive JPEG" is an expansion of the graphic file format JPEG that can be used to gradually build and save a photographically realistic image in a Web browser. In this process, already downloaded partial data quantities ALi [kByte] are decoded in several decoding steps simultaneously during downloading of the data quantity to be transferred
                              L          total                =                              1            1.024                                          MByte            kByte                                                        ∑                              i                =                1                            N                                                  Δ                                                                                L                  i                                                                  [                  MByte                  ]                                                                                (        1        )            of an image file from a central network server to the local client computer of a network user so that ever more detailed preview images Vi of the graphic to be reconstructed can be displayed until the total image file has been downloaded from the network server. The resolution of the graphic will become gradually ever finer during the loading process and the resulting picture will be sharper until the predefined resolution RB is achieved through the quantization of the original image. An advantage of this process is that a person viewing a Web page with embedded graphic elements will get an initial visual impression of the image file when the download begins and does not have to wait until the complete image has been transferred. The goal is                to shorten the elapsing wait time for the graphic display of useable j-th version of a preview image Vi for creating an early visual impression of the downloaded image file
                                          T            W                                          (            j            )                                                        :                    =                                    ∑                              i                =                1                            j                                                  Δ                                                                                t                                      w                    ,                    i                                                                                [                  s                  ]                                                                                (                  2                    a                )                            so that the network user already at an early point in time ti of the loading process can have valuable image information from the data quantity transferred up to that point
                                                                        L                ist                                                          (                j                )                                                                :                                =                                                    ∑                                  i                  =                  1                                j                                                          Δ                                                                                L                  i                                                      =                                                            L                  gas                                ·                1.024                                                          kByte                MByte                                                                            ∑                                      i                    =                    1                                    j                                                                  Δ                                                                                l                      i                                                                                [                      kByte                      ]                                                                                with                                                                          j                    =                      {                          1              ,                              2                                                                                …                                                                                ,              N                        }                                              (                  2                    b                )                            made available whereby
                    Δ                                                            l          i                                  :                                  =                                    100              ·                              1                1.024                                                                                MByte                kByte                            ·                                                Δ                                                                                l                    i                                                                    L                  gas                                                                                (                  2                    c                )                            which designates the percentage increase of the partial data quantity received and decoded in the decoding step Di.        to transparently display the progress of the image transfer achieved at each decoding step Di at the time points ti, which shows an improvement of the image quality, and        controls the loading process interactively, if necessary, to cancel or continue.
In order to achieve this, the images used with progressive JPEG are split up as in the baseline JPEG process in 8×8 blocks and are transformed using the Discrete Cosinus Transformation (DCT). According to the quantification, for which parameters may be set, each block will not be coded immediately but will first be temporarily saved in a data buffer until all blocks contained in the image are quantified. The buffer content will then be coded in several steps. Therefore there is no sequential coding of the individual blocks as in the baseline JPEG process. The loading and decoding of partial data quantities for display of rough preview images with gradually refined resolution proceeds significantly faster then a line-by-line image composition for reconstructing the fine resolution of the original image.
The technical problem encountered in decoding in this context lies in the optimal determination of the time distances of two immediately consecutive decoding steps Di−1 and Di that must be selected in such a way that the mean data reception rate R, the improvements in image quality Q achieved in the individual coding steps and the available performance capacity and the relative load (burden)
                    ρ        =                              100            ·                                          T                D                                            T                W                                              =                      100            ·                                                                                ∑                                          i                      =                      1                                        N                                                                          Δ                                                                                t                                              D                        ,                        i                                                                                ∑                                          i                      =                      1                                        N                                                                          Δ                                                                                t                                              W                        ,                        i                                                                                [              %              ]                                                          (                  3                    a                )            of the applied decoding and display system can be taken into account. In this instance,
                                          T            W                                          :                          =                                            ∑                              i                =                1                            N                                                  Δ                                                                                t                                  W                  ,                  1                                                              =                                    t              N                        -                                          t                0                                                                                [              s              ]                                                          (                  3                    b                )            designates the total required wait time from the beginning of the download process to the time to=0 s until the display of the final version Vn of maximum resolution RB of an image at time tN and
                              T          D                                              :                    =                                    ∑                              i                =                1                            N                                                  Δ                                                                                t                                      D                    ,                    i                                                                                [                s                ]                                                                        (                  3                    c                )            is the total required time span for decoding and graphic visualization of this final version VN, whereby
                              t          D                                  ≤          1                                  T          W                                    (                  3                    d                )            must be valid; Δtw,i is the wait time between both decoding steps Di−1 and Di, Δthd D,i is the actual required computation time for decoding and graphic visualization of the partial data quantity ΔLi and
                              ρ          i                =                  100          ·                                                    Δ                                                                                t                                      D                    ,                    i                                                                              Δ                                                                                t                                      W                    ,                    i                                                                                [            %            }                                              (                  3                    e                )            the usage of the decoding and display system at the time interval Δtw,i which may not be greater than 100%. The following must also apply
                              Δ                                                                          t                          D              ,              i                                                        ≤          1                                  Δ                                                                          t                          W              ,              i                                                                                ∀                          i              .                                                          (                  3                    f                )            Conventional processes used in the current state of technology usual determine the time durations ΔtD,l between the time points ti−1 and ti of sequential decoding steps Di−1 and Di either independently from the received data quantity List (j) (Version 1), the decoding steps are implemented at regular time distances ΔtD (Version 2) or use a combination of both processes (Version 3). As is explained in the following, these methods run into technologically conditioned limits.
When executing version 1, a procedure executed to determine the time distancesΔtD,i≡ΔtW,i:=ti−ti−1≠const.[s] (for iε[1,2, . . . , N}  (4)of sequential decoding processes Di−1 and Di starts the i-th decoding (Di) and display step (Vi), when an established, but variable, data quantity ΔLi of progressively coded image data is available to the decoding and display system. So, as an example, the first decoding step Di is executed after the first block B1 of progressively coded image data is received by the decoding system. The partial data quantity ΔL1 of the first block B1 is thereby an optional system parameter. Further decoding steps D2 through Dn are implemented after further blocks B2 thru Bn, whose sizes ΔL2 through ΔLn depend respectively on the sizes ΔL1 through ΔLN−1 for the previously received blocks B1 through Bn−1 and their system parameters are determined suitable, were received by the decoding system. Such a determination of the decoding distances Δtp,l takes into account the mean transfer rate
                    R        =                              8                                                      Bit                Byte                            ·                                                L                  ges                                                  T                  W                                                                                =                      8                                                      Bit                Byte                            ·                              1                1.024                                                                                Mbyte                kByte                            ·                              1                                  T                  W                                            ·                                                ∑                                      i                    =                    1                                    N                                                                  Δ                                                                                L                      i                                                                                [                                          Mbit                                                                    /                                                                  s                                        ]                                                                                (        5        )            the total data quantity received Ltotals during the time Tw only indirectly via the system parameters ΔLi. Then there is a slow reception of the data at long wait times Δtw,l between the decoding steps Di−1 and Di, whereas there is a fast reception of data at very short wait times Δtw,i. In the latter case, the decoding processes can no longer be executed in a timely manner due to the limited performance capacity of the decoding system is some circumstances. In order to avoid this, in many systems the instant value
                                          R            i                    =                      8                                                      Bit                Byte                            ·                              1                1.024                                                                                MByte                kByte                            ·                                                Δ                                                                                L                    i                                                                    Δ                                                                                t                                          D                      ,                      i                                                                                (                                    for                                                                                i                        ∈                          (                              1                ,                                  2                                                                                …                                ,                N                            )                                                          (        6        )            of the data rate R of received image data form a system parameter that is either regularly measured or is recognized as an estimate by the decoding system.
If, as in version 2, the display steps Vi are executed in regular, constant time intervals Δtp, the total image data quantity received at the time tj of display by the decoding and display system
                                                                                L                  ist                  ′                                                                  (                  j                  )                                            :=                                                                    j                    ·                    Δ                                                                                L                                =                                  1.024                                                                                k                                                                                Byte                                            MByte                                        ·                    j                    ·                                          L                      ges                                        ·                    Δ                                                                                l                                                                                [                                          k                                                                                Byte                                        ]                                                                                (                                                      with                                                                                j                                    ∈                                      {                                          1                      ,                      2                      ,                      …                                                                                ,                      N                                        }                                                  )                            ,                                                          (                  7                    a                )            whereby
                              Δ                                                              l                :=                              100            ·                          1              1.024                                                                                MByte                              k                                                                                Byte                                      ·                                                            Δ                                                                                L                                                  L                  ges                                                                                [              %              ]                                                          (                  7                    b                )            with ΔL1=ΔL2= . . . ΔLi= . . . =ΔLN=:ΔL [kByte]  (7c)
the increase as a percentage of the received data and designated in the individual decoding steps as decoded constant partial data quantities ΔL, will be decoded and graphically visualized. The time intervalstD,i:=ti−ti−1=const. [s] (for iε{1,2, . . . , N})  (8a)between two consecutive decoding steps Di−1 and Di, wherebyΔtD,1=ΔtD,2= . . . ΔtD,i= . . . ΔtD,N=:ΔtD[s] and ΔtD,1≦ΔtW,1  (8b)is valid, form a system parameter of the decoding system and also take into account the performance capacity of the decoding system. In the case of such a manner of proceeding, the data rate
                                                                        R                I                            =                              8                                                                      Bit                    Byte                                    ·                                      1                    1.024                                                                                M                                                                                Byte                                                              k                                                                                Byte                                                        ·                                                            Δ                                                                                L                        i                                                                                Δ                                                                                t                                                  W                          ,                          i                                                                                =                                                      8                                                                                Bit                        Byte                                            ·                                              1                        1.024                                                                                M                                                                                Byte                                                                          k                                                                                Byte                                                                    ·                                                                        Δ                                                                                L                            i                                                                                Δ                                                                                t                            W                                                                                ·                                              N                        N                                                                              =                                                            8                                                                                Bit                          Byte                                                ·                                                                              L                            ges                                                                                T                            W                                                                                =                                          R                                                                                [                                              M                                                                                Bit                                                                          /                                                                        s                                            ]                                                                                (                                                with                                                                                i                                ∈                                  {                                      1                    ,                    2                    ,                    …                                                                                ,                    N                                    }                                            )                                                          (        9        )            of the received data will implicitly be taken into account. At a small data rate Ri of a received partial data quantity ΔLi, the visual improvement of the displayed image between decoding steps Di−1 and Di is small, whereas a high data rate Ri of the received partial data quantity ΔLi leads to a dramatic improvement ΔQi of the image quality Q. An overload due to the limited performance capacity of the decoding system is hereby excluded. There is a disadvantage, however, in that the usage p of the decoding system remains constant with respect to time independently of the data rates Ri of the received partial data quantities ΔLi
A combination of both manners of proceeding according to version 3 leads to usage of the decoding system that can be modified with respect to time.
The usage pi is dependent on the partial data quantity ΔLi received in the time interval Δtw,i.
Common to all three versions, however, is the fact that statistical and visual properties of a transferred image cannot be taken into account. It may therefore occur that consecutive display steps Vi−1 and Vi can lead to no discernable improvement of the image resolution RB,l to the viewer.
FIG. 1 shows a typical course of image quality Q depending on the percentage
                    l        :                  100          ·                      1            1.024                    ·                                    M                                                                                Byte                                      k                                                                                Byte                                ·                                    L                              L                ges                                                                                [            %            ]                                              (        10        )            of the received data quantity L [kByte] of progressively coded images compressed in the JPEG 2000 format referring to the total data quantity Ltotal to be transferred. As a statistical quality metric
                              Q          1                :                  100          ·                                    (                              1                -                                                      e                    i                                                        e                    0                                                              )                                                                          [            %            ]                                              (                  11                    a                )            for the current image resolution RB,i is, in this instance, the mean square error (MSE)
                                                                        e                1                            :=                                                1                                                            μ                      max                                        ·                                          v                      max                                                                      ·                                                      ∑                                          μ                      =                      1                                                              μ                      max                                                                                ∑                                              v                        =                        1                                                                    v                        max                                                                                (                                                                              v                                                          n                              ,                                                              μ                                                                                v                                                                                -                                                      v                                                          i                              ,                                                              μ                                                                                v                                                                                )                                            2                                                                                (                                                for                                                                                i                                ∈                                  {                                      1                    ,                    2                    ,                    …                                                                                ,                    N                                    }                                            )                                                          (                  11                    b                )            between the final version Vn of an image to be reconstructed whose image quality Qn ideally corresponds to the image qualityQorig:=100%  (11c)of the transferred original image Vorig, and forms the basis of the respectively viewed version of a preview image Vi at lower resolution and has been normalized to a quality range between 0% and 100%. In this case, VN,uv designates the pixel value of the original image Vorig to be transferred for the pixel (μ,v), Vi,uv the pixel value of the i-th preview image Vi for the pixel (μ, v) and
                                          e            0                    ≡                      e            max                          :=                              1                                          μ                max                            ·                              v                max                                              ·                                    ∑                              μ                =                1                                            μ                max                                                                                ∑                                  v                  =                  1                                                  v                  max                                                                                V                                  N                  ,                                      μ                                                                                v                                                  2                                                                        (                  11                    d                )            the maximum possible error. A quality metric of 100% provides the best available quality that can be achieved when the total image data quantity Ltotal has been completely and successfully transferred. In this case (i=N) the mean square error ei is ideally equal to zero:eN=0.  (11e)An image quality of 0% exists when not image data has been transferred. In this case, (i=0) the mean square error ei achieves a maximum value of emax.
FIG. 2 shows another diagram for displaying a typical course of the statistical image quality Q depending on the percentage l of the received data quantity L of progressively coded image data compressed in the JPEG 2000 format referring to the total data quantity Ltotal (in MByte) to be transferred. Here, in addition to the continual function course Q(l), the time ti of the decoding procedures Di with the associated percentage of the data quantity share Δll and image quality values AQi for a statistically equal quality improvementΔQi:=h(Δli)=Qi−Qi−1(for iε{1,2, . . . N,})  (12)of 10.00% per decoding step i has been specified, whereby both relationshipsQi:+Q(li) and  (12a)Qi=1:=Q(li−1)  (12b)give the image quality of the preview images Vi and Vi−1. This shows that when there is a small portion Δll the quality increase AQi is high, i.e. the data quantity ΔLi that must be received between two improvement steps Di−1 and Di is initially relatively small and increases with the increase of the existing data quantity List(j) at the point in time tj.
As can be seen in FIG. 2, a large number N of decoding steps Di for a proportionally small quantity Δll of data within the framework of the determination of the decoding step Di described above in accordance with version 1 leads to an overload of the decoding system.
In practice, the courses of the image quality Q illustrated in FIGS. 1 and 2 result from statistically mean and normalized values of a random quality metric. The relationship indicated above between the image quality Q and the mean square error e is therefore understood for purely illustrative purposes. In fact, the normalized image quality courses Q(l) are stored in a data memory and are determined independently of the transfer.

Process and functional unit for the optimization of displaying progressively coded image data


An image display device projects lights emitted from each of two two-dimensionally light emitting type photoelectric devices onto first and second light diffusing bodies, and projects and images transmitted images of the light diffusing bodies onto the retina in the respective eyeballs of the user. The display device includes one light source, a first polarization beam splitter dividing light emitted from the light source into P-polarized light and S-polarized light, and an optical system which leads each of the P-polarized light and S-polarized lights respectively to the two photoelectric devices thereby illuminating the two photoelectric devices. The optical system leads polarized light to each of the two photoelectric devices via a second polarization beam splitter and a λ/4 plate, and leads reflected lights to the relay optical system via the λ/4 plate and the second polarization beam splitter.

There are many kinds of image display devices, e.g., a television, a personal computer, a projector, a video camera, and a cell phone; however, such conventional image display devices are limited in their display size, and thus such a wide range of image as is actually viewed by human eyes has not been able to be obtained from such displays.
On the other hand, as portable displays, an eyeglass type display and a head mount type display, both called a wearable display, are known. As a wearable display, there is known a method in which, as shown in FIG. 28(a), small half mirror 40 is arranged at a portion of the field of view, and an image outputted from image output device 39 such as a plasma display or a liquid crystal is, via projection optical system 38, deflected by half mirror 40 and is projected onto the retina of the eyeball. This method uses the half mirror and thus is such a system (the first type) as the image outputted from image output device 39 is viewed as floating in a portion of the field of view. However, as the field of view angle, a few degrees can only be obtained. As the application of this type wearable display, presentation of the image information of a cell phone has been conceived, for example.
On the other hand, as a method to obtain a little larger image information, there is a system as shown in FIG. 28(b). In this method, a large optical element 41 is arranged before the eyeball, and the image outputted from image output device 39 is, via a plurality of reflecting surfaces and projection optical system 42, projected onto the retina of the eyeball. While with respect to this type of method, a relatively large field of view angle (about 15 to 22.5 degrees) can be obtained, only the type in which the field of view is completely obstructed has been proposed. Thus, as the applicable method thereof, there have been proposed a system (the second type) in which this type image display device is detachably disposed before one eye and is used as a display as a wearable personal computer, and a system (the third type) in which the same image display devices are each independently positioned before each of the eyes and are used instead of a television or a projector.
The above-described three types of the prior art image display devices were respectively expected to substitute, as a wearable display, the cell phone, the notebook computer, and the television or the projector. However, as a matter of fact, while they have the advantage of wearableness, they do not differ much from the conventional display devices with respect to the size of the display field of view, and when considering the bother of wearing them, the eyestrain with the field of view being obstructed, and the weight to be supported by the ears or the head, they have the disadvantage that they are featured in conspicuous defects. Furthermore, even in the case of the display devices having a large field of view angle, the field of view angle is in the range of about ±15 to ±22.5 degrees, and thus a sense of realism could be obtained.
On the other hand, as systems describing the method to obtain a large field of view by allowing the weight to increase and by using a plurality of lenses as the eyepiece, there are, for example, such systems as described in Japanese Unexamined Patent Publication No. 7-244246 or Japanese Unexamined Patent Publication No. 2001-311910, and in such systems, a field of view angle of ±22.5 degrees or more can be realized. However, such systems have a wide field of view angle only in the condition that the eyeball does not move, and neither the shift of the crystalline lens from the eyepiece center that occurs when the eyeball moves nor the associated chromatic aberration is sufficiently taken account of.
In addition, with respect to these kinds of devices having a large field of view angle, because the eyepiece optical system becomes large-sized, resulting in the weight increase, and thus there arises the disadvantage that such devices no longer meet the weight requirements of the HMD type display supported by the head or of the eyeglass type display of which weight is supported by the nose and the ears like eyeglasses.

Image display device using P-polarized light and S-polarized light


A method and apparatus for rapid non-invasive determination of blood composition parameters. A blood-containing body part of a live organism is irradiated with electromagnetic radiation of near-infrared wavelength range. Spectrum values of the radiation transmitted through and reflected by the body part are measured. One or more unknown values of blood composition parameters are determined on the basis of the measured values. The transmittance spectrum of the body part is measured at several wavelengths in a first wavelength range from 700 nm to a value between 1000 and 1100 nm. The reflectance and/or interactance spectrum of the body pat is measured at several wavelengths in a second range from the value between 1000 and 1100 nm to 1800 nm. The unknown values of blood composition parameters are determined on the basis of a single spectrum including spectrum values of said transmittance spectrum and spectrum values of said reflectance and/or interactive spectrum.

1. Field of the Invention
The subject matter of the invention is a method and apparatus for rapid non-invasive determination of blood composition parameters.
2. Discussion of the Background
In medical diagnostics it is often necessary to determine various blood composition parameters, e.g. blood components like glucose, protein, albumin, creatinine, carbamide, cholesterol, triglyceride, cholinesterase, haemoglobin, etc. Measuring the glucose component is especially important, because diabetes mellitus seems to be considered as a widespread disease. For treatment of diabetes mellitus, glucose content of the blood must be regularly monitored. In line with up-to-date treatment principles, efforts must be made to close the gap as much as possible between the actual glucose component and the physiological one. Therefore, frequent blood sugar measurement is indispensable. Even under hospital conditions it is a frequent occurrence that only the determination of the glucose component is necessary. Today some diabetics determine their blood sugar themselves at home. This is primarily becoming a habit in areas having a developed health culture, but an objective should be to allow this opportunity for all patients.
There are widely used instruments which determine the glucose in blood by photometry using a blood drop on paper strips saturated with reagents. However, this approach is far from being perfect, because numerous circumstances, like the age of the paper strips, the temperature, the period elapsing between taking the blood sample and dripping it on the paper, make an unfavourable influence on the accuracy of measurement. But, the greatest concern is that the patient must be pricked in each case, because blood is required for the determination. Either the patient pricks himself or this is done by somebody else, sterility must be ensured. Even in the case of a patient really intending to cooperate, a very serious worry is the fact of being pricked. For a young diabetes patient, the glucose in blood must be controlled several times a day and this represents a lot of pricks throughout his lifetime as diabetes cannot be cured at the moment.
Therefore, it would be a major benefit to be able to determine blood components and especially glucose content by a non-invasive technology and, thereby, to eliminate the need of pricking the patient. The glucose component could be determined more frequently than now, which would enable more accurate adjustment, and so complications of diabetes could be better avoided. Even patients difficult to cope with would be more liable to measure the glucose in their blood themselves, because the measurement would be absolutely painless. Furthermore, infection could be avoided with total security. Materials necessary for disinfecting would not. be required neither reagents used so far for determining blood sugar, and this would have high significance also from an environment protection aspect as people in many hundreds of millions are involved all over the world.
It is well known that the spectrum of electromagnetic radiation reflected by or transmitted through a material contains valuable information about the composition of the examined material. For obtaining this information, numerous mathematical methods are available. Of these, worth mentioning are the "multiple linear regression" (MLR) method, which describes the correlation between spectrum values measured at some characteristic wavelengths and a component to be determined, as well as the "principal component regression" (PCR) and "partial least squares regression" (PLSR) methods which two latter methods describe the correlation between a component to be determined and so-called latent variables, where each of the latent variables can be generated as a function of all measured spectrum values in the form of a linear equation.
Organic materials, including body tissues, are most transparent in the near-infrared (NIR) wavelength range. It has already been suggested to use NIR technology for non-invasive determination of glucose in blood. Such apparatus have been described, for example, in U.S. Pat. Nos. 5,028,787, 5,777,476, 5,086,229, 5,237,178 and 5,362,966. These apparatus use NIR technology to measure glucose in blood in a part of the human body in transmission or interactance mode of operation, in a wavelength range from 600 to 1100 nm, where the penetration ability of electromagnetic radiation is the highest. In this wavelength range, the sensitivity of silicon detectors is also satisfactory. The apparatus described comprise infrared radiation sources, means for guiding the radiation to the examined part of the body, narrow-band filters, elements to position the body part in a measuring instrument, elements to measure the thickness of the body part, elements to measure and provide signal about the temperature of the body part and the environment, as well as detectors, amplifiers, signal processors and display units serving for measuring the radiation exiting from the body part. In signal processing, it has been recommended to use first and second derivatives of the measured spectrum and also a normalisation. As the point of measurement, the distal phalanx directly behind the nail, the nose, the earlobe and the vein visible at the wrist and the elbow-joint have been proposed.
A transmission detection technique in the long wavelength infrared range has been suggested in U.S. Pat. No. 5,313,941 to monitor glucose and other blood constituents in a non-invasive manner. Short pulses of relatively high energy and narrow optical bandwidth are sent through a finger which pulses are synchronised with the heartbeat period. The apparatus comprises a separate cardiac monitor which can be an optical plethysmograph or an electrocardiogram.
A spectrophotometric method for non-invasive measurement of component concentrations in body parts has been described in EP-A1-0 636 876. Pulsed laser light of different wavelength are projected toward a body part and the light exiting from the body part is detected. Then, by calculating an optimum lapse of time corresponding to an optimum path length, a quantity of the exiting light at the optimum lapse of time is determined. It has been suggested to utilize either transmitted light or reflected light or both, however, the description does not tell how to evaluate measurements if both transmitted and reflected lights are detected and what wavelengths of light are to be used.
So far, however, there is no available apparatus using NIR technology for non-invasive determination of glucose in blood that could be applied in a wide range of application with a sufficient accuracy.

Method and apparatus for rapid non-invasive determination of blood composition parameters


A device for generating a plurality of laser pulses from a recirculating single laser pulse in an optical delay line that is capable of partially transmitting the trapped pulse out of the delay line. The energy of the partially reflected trapped pulse is restored before beginning another round trip in the delay line. The time structure of an output pulse train thus generated by the device comprises a sequence of macro pulses, each comprising a plurality of micro pulses.

1. Field of the Invention
The present invention is related to the production of a laser pulse train. More specifically, the present invention provides a device that generates a plurality of laser pulses from a single laser pulse using an array of optical elements.
2. Description of Prior Art
For many applications, a high-yield electron source with excellent beam quality is needed. For example, short pulse, nearly mono-energetic, tunable x-rays may be generated by the collision of a plurality of electron bunches from a photoinjector with synchronized photon pulses in a high-power laser beam via Compton backscattering. Such x-rays have uses in medical imaging, crystallography, and designer drugs, to name a few. In addition to x-ray generation via Compton scattering, the laser pulses may be used directly or in another manner as described above in other applications such as in optical communications. Another use of a laser-triggered photoinjector is in the generation of a train of multi-bunch electrons for acceleration in linear electron-positron colliders such as the International Linear Collider or the CERN Linear Collider.
Conventional multi-cell photoinjectors are capable of accelerating short electron bunches to energies in the range of 3-30 MeV utilizing the rf pulse from a high power source with peak power typically tens of megawatts. The electron bunches are generated by laser pulses synchronous with the rf pulses. The synchronization is normally controlled by a master clock which drives both the high power rf source and the laser. Thus during each rf pulse, one electron bunch is generated and accelerated in the photoinjector. Because of the great disparity between the length of the rf pulse and that of the laser (and consequently electron) pulse, this is a very inefficient way to utilize the energy of the rf pulse. Thus in the conventional single-bunch scheme, only a single rf cycle out of thousands of cycles in an rf pulse is utilized for acceleration, even though the rf pulse length is usually much longer than the filling time of the accelerating cavities.
In principle, a train of many electron micro bunches can be accelerated synchronously in individual rf cycles within a single macro rf pulse, provided that the beam loading on the rf pulse is not severe. Such a multi-bunch acceleration scheme may require a very high rep rate laser. The repetition rate of a laser beam is inversely related to its peak power. Current technology limits the maximum rep rate of a laser with a milliwatt level of peak power to a few kilohertz, which is insufficient for the purpose of generating electron bunches typically a few nanoseconds apart for multibunch acceleration. Furthermore, even if the laser rep rate can be increased to a few hundred megahertz as required, only several thousands of these pulses would be needed during each macro rf pulse, and therefore all other laser pulses between macro rf pulses are unnecessarily wasted.
An example of a prior art approach is current work being carried out at the Rutherford Laboratory where multiple laser pulses are generated with a low-power, continuous wave (CW) laser and selected pulses are then amplified to high power using an array of pulsed amplifiers. For photoinjector application, the duration and rep rate of the amplified pulses are dictated by those of the high power rf source. Thus only the laser pulses that fall within the time structure of the pulsed amplifiers gain energy, and the rest of the CW laser pulses are discarded.
What is thus desired is to provide a multiple laser pulse train having a predetermined macro and micro time structure with an efficient device not using a CW laser.