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New Stories, Essays, and Other WritingsFrom the renowned author of "The Lottery" and The Haunting of Hill House, a spectacular new volume of previously unpublished and uncollected stories, essays, and other writings. Shirley Jackson is one of the most important American writers of the last hundred years. Since her death in 1965, her place in the landscape of twentieth-century fiction has grown only more exalted. As we approach the
$12.99The classic supernatural thriller by an author who helped define the genre First published in 1959, Shirley Jackson's The Haunting of Hill House has been hailed as a perfect work of unnerving terror. It is the story of four seekers who arrive at a notoriously unfriendly pile called Hill House: Dr. Montague, an occult scholar looking for solid evidence of a "haunting"; Theodora, his lighthearted
$9.99The Lottery, one of the most terrifying stories written in this century, created a sensation when it was first published in The New Yorker. "Power and haunting," and "nights of unrest" were typical reader responses. This collection, the only one to appear during Shirley Jackson's lifetime, unites "The Lottery:" with twenty-four equally unusual stories. Together they demonstrate Jack son's
$9.99In the uproarious sequel to Life Among the Savages, the author of The Haunting of Hill House confronts the most vexing demons yet: her childrenIn the long out-of-print sequel to Life Among the Savages, Jackson's four children have grown from savages into full-fledged demons. After bursting the seams of their first house, Jackson's clan moves into a larger home. Of course, the chaos simply moves
$9.99In a hilariously charming domestic memoir, America's celebrated master of terror turns to a different kind of fright: raising childrenIn her celebrated fiction, Shirley Jackson explored the darkness lurking beneath the surface of small-town America. But in Life Among the Savages, she takes on the lighter side of small-town life. In this witty and warm memoir of her family's life in rural Vermont,
$12.99Shirley Jackson, author of the classic short story The Lottery, was known for her terse, haunting prose. But the writer possessed another side, one which is delightfully exposed in this hilariously charming memoir of her family's life in rural Vermont. Fans of Please Don't Eat the Daisies, Cheaper by the Dozen, and anything Erma Bombeck ever wrote will find much to recognize in Shirley Jackson's
The Witchcraft of Salem VillageStories of magic, superstition, and witchcraft were strictly forbidden in the little town of Salem Village. But a group of young girls ignored those rules, spellbound by the tales told by a woman named Tituba. When questioned about their activities, the terrified girls set off a whirlwind of controversy as they accused townsperson after townsperson of being witches. Author Shirley Jackson
$9.99Shirley Jackson's third novel, a chilling descent into multiple personalitiesElizabeth is a demure twenty-three-year-old wiling her life away at a dull museum job, living with her neurotic aunt, and subsisting off her dead mother's inheritance. When Elizabeth begins to suffer terrible migraines and backaches, her aunt takes her to the doctor, then to a psychiatrist. But slowly, and with Jackson's
$9.99Before there was Hill House, there was the Halloran mansion of Jackson's stunningly creepy fourth novel, The SundialWhen the Halloran clan gathers at the family home for a funeral, no one is surprised when the somewhat peculiar Aunt Fanny wanders off into the secret garden. But then she returns to report an astonishing vision of an apocalypse from which only the Hallorans and their hangers-on will
$12.99The compelling novel that began Shirley Jackson's legendary careerPepper Street is a really nice, safe California neighborhood. The houses are tidy and the lawns are neatly mowed. Of course, the country club is close by, and lots of pleasant folks live there. The only problem is they knocked down the wall at the end of the street to make way for a road to a new housing development. Now, that's not
$12.99Shirley Jackson's chilling second novel, based on her own experiences and an actual mysterious disappearanceSeventeen-year-old Natalie Waite longs to escape home for college. Her father is a domineering and egotistical writer who keeps a tight rein on Natalie and her long-suffering mother. When Natalie finally does get away, however, college life doesn't bring the happiness she expected. Little by
$9.99The classic supernatural thriller by an author who helped define the genre First published in 1959, Shirley Jackson's The Haunting of Hill House has been hailed as a perfect work of unnerving terror. It is the story of four seekers who arrive at a notoriously unfriendly pile called Hill House: Dr. Montague, an occult scholar looking for solid evidence of a "haunting"; Theodora, his lighthearted


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Electronic device and lead frame
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A lead frame facilitates the handling, positioning, attachment, and/or continued integrity of multiple dies, without the use of multiple separate parts, such as jumpers. The lead frame includes a number of structures, each of which is attached to at least one lead. At least one receiving surface, arranged to receive a die, is associated with each structure. When dies are disposed on the receiving surfaces, anodes are similarly-oriented. A number of fingers are attached to the lead frame, and one or more electrode contact surfaces are attached to each finger. Each electrode contact surface can be positioned (for example, bent) with respect to one receiving surface, to facilitate electrical connection between the anode of a die and a lead. The lead frame may be used in connection with surface- and through-hole-mountable electronic devices, such as bridge rectifier modules.
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Dental amalgams contain approximately 50% metallic mercury and emit small quantities of mercury vapor. Controversy surrounds whether fetal exposure to mercury vapor from maternal dental amalgams has neurodevelopmental consequences.
Maternal amalgam status during gestation (prenatal mercury vapor exposure) was determined retrospectively on 587 mother-child pairs enrolled in a prospective longitudinal cohort study of effects of prenatal and recent postnatal methylmercury exposure on neurodevelopment. Covariate-adjusted associations were examined between 6 age-appropriate neurodevelopmental tests administered at 66 months of age and prenatal maternal amalgam status. Models were fit without and with adjustment for prenatal and recent postnatal methylmercury exposure metrics.
Mean maternal amalgams present during gestation were 5.1 surfaces (range 1-22) in the 42% of mothers with amalgams. No significant adverse associations were found between the number of prenatal amalgam surfaces and any of the 6 outcomes, with or without adjustment for prenatal and postnatal methylmercury exposure. Analyses using our secondary metric, prenatal amalgam occlusal point scores, showed an adverse association in males only on the Letter Word Recognition subtest of the Woodcock-Johnson Tests of Achievement, and several apparently beneficial associations for females only.
This study provides no support for the hypothesis that prenatal mercury vapor exposure from maternal dental amalgams results in neurobehavioral consequences in the child. These findings need confirmation from a prospective study of co-exposure to methyl mercury and mercury vapor.
The use of amalgams for dental restorations was introduced over 160 years ago. Favorable physical properties, superior durability, and economical cost made amalgam the preferred restorative material for billions of teeth. Recent studies indicate amalgam continues to be used frequently today. A dental practice-based research network (DPBRN) encompassing 229 dentists in Alabama, Mississippi, Florida, Georgia, Minnesota, Denmark, Norway, and Sweden, reported 38% of all recently placed restorations were amalgam, accounting for 45% of premolar restorations and 47% of molar restorations.1 Dentists participating in the Northwest PRECEDENT DPBRN (Oregon, Washington, Idaho, Montana, and Utah) reported using dental amalgam for 28% of restorations placed in children and adolescents, and for 22.7% of restorations placed in adults over the preceding 12 months.2 Placement of dental amalgam restorations remains significant in all age groups, including children and women of child-bearing age.
Dental amalgam is composed of approximately 50% metallic mercury, an inorganic form of mercury. Amalgams present in the oral cavity continuously expose an individual to small amounts of mercury vapor (Hg0) released from the surface over the lifetime of the restoration.3 Chronic exposure to higher levels of Hg0 is known to result in neurotoxicity consisting of various sensory, motor, cognitive and personality disturbances, but the lowest level of exposure where such associations occur is not presently known.3 Numerous reviews have suggested low level Hg0 exposure from dental amalgam restorations in adults is unlikely to result in adverse health effects.4-8 However, data for children is limited. Results from two randomized clinical trials in older children comparing postnatal exposure to Hg0 from dental amalgam to composite restorations found no significant differences in children with amalgam restorations on neurobehavioral assessments or nerve conduction velocity9, or in adverse neuropsychological and renal functions.10
Although Hg0 crosses the placenta, there are very limited scientific data to adequately assess whether there are health risks to the developing human fetus from maternal dental amalgams.8,11 Several animal studies suggest that adverse neurodevelopmental outcomes in offspring can be a consequence of prenatal exposure to Hg0 when exposure is at levels higher than those associated with dental restorations.12-15 Moreover, a recent study in rats found neurotoxic risk may be elevated in offspring co-exposed during gestation to Hg0 and methylmercury (MeHg), an organic form of mercury.16 Comparable human studies are lacking, as noted by an independent Scientific Committee of the European Union (2008) which stated, "with respect to populations at risk, there is a lack of information about effects in pregnant women".6 More recently, the FDA (2009) reviewed the issue of dental amalgams and neurodevelopment and issued a report entitled 'Final Regulation on Dental Amalgam'. In it the FDA similarly states "there is limited clinical information about the potential effects of dental amalgam fillings on pregnant women and their developing fetuses, and on children under six".17
To address prenatal exposure to Hg0 from amalgam, we retrospectively reconstructed the maternal amalgam status during gestation for mothers of children enrolled in the Seychelles Child Development Study (SCDS) Main Cohort. This cohort of children was of interest because they were exposed to elevated levels of MeHg both prenatally and postnatally due to a diet high in fish and had already had extensive neurodevelopmental testing. We first examined the association between children's prenatal Hg0 exposure (using maternal amalgam status as a biological marker) and test results from their 66 month test battery. We then examined the association with adjustment for prenatal and recent postnatal MeHg exposures to determine whether co-exposure to the inorganic (Hg0) and organic (MeHg) forms of mercury influenced the analyses.
The SCDS Main Cohort is a well-described group of 779 mother-infant pairs residing in the Republic of Seychelles. They were enrolled in 1989-1990 in a prospective, double-blind, longitudinal study designed to test the hypothesis that prenatal MeHg exposure from a maternal diet high in fish is related to child neurodevelopmental outcomes. At enrollment the mothers consumed an average of 12 fish meals per week.18 The children were evaluated at multiple ages through age 19 years using batteries of neuropsychological tests to determine their cognitive and neurological development.19-23 Of the original 779 mother-child pairs enrolled in the SCDS Main Cohort, 711 were evaluated at 66 months of age and were eligible to participate in this dental study. We were able to recapitulate maternal dental status in 587 mothers. This study was reviewed and approved by the institutional review boards of the University of Rochester, Rochester, NY, and the Ministry of Health, Republic of Seychelles. Informed consent/assent was obtained from all study participants.
In the Republic of Seychelles dental care is free and most residents utilize the national dental facilities where comprehensive historic records are maintained. Approximately 10 years after the birth of the child, mothers were recalled and their dentition was clinically examined for the presence of amalgam restorations. Subsequently, dental personnel completed a retrospective abstraction of the mother's dental records. They specifically addressed placement and disposition of amalgam restorations.
The detailed strategy utilized to reconstruct the maternal dental amalgam status during gestation is shown in Table 1. In brief, amalgam restorations with documentation of placement prior to pregnancy and presence after the child's birth were considered as being present during gestation, as were amalgams known to have been placed during gestation. Amalgams documented as being placed prior to pregnancy, but with no further proof of retention, and also amalgams with no history of placement, but present at the time of examination, were considered as 'possibly' present during gestation. Amalgams known to have been initially placed after the birth of the child were excluded.
Our primary metric of prenatal Hg0 exposure was the total number of amalgam surfaces present in the mother during gestation. This metric takes into account all surfaces of amalgam available for Hg0 release and has been extensively used as a measure of exposure.10,24-30 We also used a secondary exposure metric modified from the "amalgam points" scoring of Olstad et al.31 For this metric we considered only the occlusal surfaces of amalgams on premolars and molars, and assigned a score of 1 for small size occlusal amalgams such as pits, 2 for medium size occlusal amalgams on premolars, and 3 for large size occlusal amalgams on molars. Significant release of Hg0 from amalgams during chewing has been well documented and likely occurs primarily from the occlusal amalgam surfaces.32 Maserejian and coworkers studied various amalgam exposure measures in children and found the metric that included posterior occlusal surfaces to be the best predictor of cumulative urinary Hg excretion, the common biomarker of Hg0 exposure.30 The summed scores constitute our "occlusal points" score and are more representative of the surface area available to actively release Hg0 from amalgams during chewing.
To account for the uncertainty regarding the true maternal gestational amalgam status in this retrospective reconstruction, we determined two levels of exposure to the amalgam metrics in our statistical models (Table 1). The Lower Exposure Limit (LEL) is the total of all amalgam surfaces or occlusal points with a high likelihood of having been present during gestation, while the Upper Exposure Limit (UEL) includes all the LEL points or surfaces, plus those amalgams possibly present during gestation.
We also created indicator variables for whether any amalgam surfaces or any occlusal points were placed during pregnancy. These variables were considered in secondary models.
Prenatal MeHg exposure was previously determined by assessing the concentration of total mercury (THg) in a segment of maternal hair growing during gestation.19 Recent postnatal MeHg was previously determined by measuring THg in the 1 cm segment of hair closest to the child's scalp at the time the test battery was administered.21 Greater than 80% of THg in hair samples from a fish-eating population is in the form of MeHg, and THg is a commonly used marker of MeHg exposure.33,34,35 Mercury concentrations in hair correlate with consumption of fish, but not with Hg0 or the number of amalgam restorations.26,36,37,38 Maternal amalgam status and maternal THg therefore represent separate and discreet exposure metrics for prenatal Hg0 and prenatal MeHg, respectively. Exposure levels of other toxicants in Seychelles are low. Lead levels in whole blood from Seychellois children and mothers were determined previously to be less than 0.48 μmol/L (10 μg/dL).33 Levels of polychlorinated biphenyls in blood from a subset of 49 cohort children at age 66 months were below the limit of detection (0.2 ng/mL).21
At age 66 months a comprehensive test battery was administered to the children.21 The test battery assessed overall intelligence [General Cognitive Index (GCI) of the McCarthy Scales of Children's Abilities (MSCA)]39, expressive and receptive language ability [Preschool Language Scale (PLS) Total Score]40, reading and arithmetic achievement [Letter Word Recognition and Applied Problems subtests of the Woodcock-Johnson (W-J) Tests of Achievement]41, drawing and copying to measure visual-spatial ability (Bender Gestalt test using the Koppitz scoring protocol)42, and the child's social and adaptive behavior [Child Behavior Checklist (CBCL)]43. For the GCI, PLS, and both W-J Tests of Achievement a higher score indicates better performance. For the Bender Gestalt and CBCL a lower score indicates improved performance
Covariates measured during the evaluation included sex, birth weight, maternal age, the preschool version of the Home Observation for Measurement of the Environment (HOME: an in home observation that rates quality of the home environment and interactions between parent and child)44, Hollingshead Four- Factor SES45 (an index combining educational level and job classification of both parents), pure tone hearing thresholds on the children, caregiver IQ (Raven Standard Progressive Matrices, a culture-free test which uses visual geometric drawings of increasing complexity)46.
We examined the covariate-adjusted associations between each of the six outcomes and prenatal Hg0 exposure, using four different estimators of prenatal Hg0 exposure: the number of amalgam surfaces using the LEL, amalgam surfaces using the UEL, occlusal point score using the LEL, and occlusal point score using the UEL. Models for each outcome and Hg0 exposure metric were fit without and then with adjustment for prenatal and recent postnatal MeHg exposure metrics. Each model was first examined for an interaction between the prenatal Hg0 metric and sex. If the interaction was significant, then the model was reported with the interaction. Otherwise, the model was rerun and reported without this interaction. The Hg0 metric by sex interaction allows the slope relating the Hg0 metric to the outcomes to differ for males and females. Because there was no biological reason to expect non-additive effects of prenatal Hg0 and MeHg exposures, we did not examine an interaction between MeHg exposure and the prenatal Hg0 metric.
All regression models adjusted for the same covariates as in the primary analysis for this cohort, which were chosen based on their potential to impact the association between Hg and outcomes.21 The child-related covariates included sex, birth weight, child's medical history, and child's hearing status. The maternal and family-related covariates included maternal age, HOME score, Hollingshead SES, and caregiver intelligence (Raven score). All covariates were treated as continuous variables except for sex, child medical history, and the child's hearing level. The latter was modeled in three discrete levels (0-25, 26-35, and >35 dB). We included the postnatal MeHg by sex interaction only for the Bender Gestalt Errors outcome, to be consistent with previously reported results.21 Models for each outcome were fit using subjects with complete covariate and dental data, and non-missing values for the outcome.
Only results from significant models (p≤ 0.05) are reported. Models that are significant may have significant and/or non-significant predictors within them. Thus prenatal Hg0 may or may not be a significant predictor in any given model. Model assumptions were checked using standard methods, and if violated, transformations were considered.47 Model results include outlying values, when they are present.
Additional, secondary models were fit that adjusted for whether the mother had any amalgams or occlusal points placed during pregnancy.
Complete dental and covariate data were available on 587 women. Some children were unable to complete all the tests. Summary statistics for all continuous variables, both overall and by sex, are presented in Table 2. In the LEL group, 249 mothers (42.4%) had at least one amalgam. Three of these had only non-occlusal amalgams and thus no occlusal points, while the remaining 246 had at least one occlusal amalgam. For both the LEL and UEL, the occlusal point score and number of amalgam surface metrics were highly correlated (r= 0.928 for the LEL and r= 0.916 for the UEL, data not shown).
Prenatal and recent postnatal MeHg exposure levels for this subset of the original cohort were comparable with the original full cohort.21 The mean maternal hair THg level was 6.7 (±4.4) ppm (range 0.5-22.8 ppm) for the 587 subset mothers with full covariate data. The hair THg level in this subset of children at 66 months (n = 587) was 6.4 (±3.3) ppm (range 0.9-25.8 ppm). There was no association between maternal LEL surfaces and prenatal (r = 0.01) or postnatal (r = -0.07) MeHg (hair THg) exposure. The means of the outcomes and covariates by prenatal MeHg and Hg0 exposure categories are shown in Table 3.
All models were significant for both amalgam surfaces and points. We first used the number of amalgam surfaces to estimate regression coefficients for the six outcome variables for covariate-adjusted models using the LEL without (model 1) and with (model 2) adjustment for prenatal and postnatal MeHg. These results are presented in Table 4.
Amalgam surfaces were not significantly associated with any outcome, either without or with adjustment for prenatal and recent postnatal MeHg. However, there was a significant interaction of sex by LEL amalgam surfaces for the GCI endpoint (p = 0.04) after adjusting for prenatal and recent postnatal MeHg and covariates. For the GCI, the amalgam slope was positive for females (0.31, 95% CI: -0.09 to 0.72) and negative (-0.24, 95% CI: -0.59 to 0.12) for males, but neither slope was significantly different from zero (Table 4). The relationship between LEL amalgam surfaces and GCI is illustrated in Figure 1. The plot suggests that for a small number of amalgam surfaces, the GCI outcomes are similar for both sexes. However, as the number of maternal amalgam surfaces increases, males are predicted to perform less well, while females are predicted to have better performance. As expected, a higher HOME score was a very significant predictor of improved scores in all models and higher SES and caregiver IQ were also significant predictors of improved scores in some models.
Similar results (coefficients and p-values) were obtained using the UEL number of amalgam surfaces as the metric of Hg0 exposure (data not shown). The UEL amalgam surface metric was not a significant predictor for any outcomes. When adjusting for UEL amalgam surfaces, increasing recent postnatal MeHg exposure was associated with significant improvement in both sexes in the same outcomes: GCI (0.35, p = 0.02), PLS Total Score (0.22, p = 0.01), and W-J Applied Problems (0.57, p = 0.01). In addition there were fewer Bender Gestalt Errors with increasing postnatal MeHg exposure (-0.20, p = 0.01) in male children.
We next examined the association between our secondary metric, the occlusal amalgam point score, and the same outcomes. Results for both LEL and UEL adjusting for prenatal and recent postnatal MeHg and covariates (Model 2) are given in Table 5. The amalgam occlusal points-by-sex interaction term was significant for the GCI (LEL and UEL) and for three other outcomes at UEL (PLS Total Score and the W-J for both the Applied Problem and Letter-Word Recognition subtests). For these outcomes, the slope for amalgam points was significantly different for males and females. Males performed less well on each outcome compared to females as occlusal points increased. However, a significant interaction does not necessarily mean that the amalgam point slope was significantly different from zero (i.e. significantly adverse or beneficial) for either males or females. There was a significant adverse association of the UEL occlusal point score in males on a single outcome (W-J Letter Word Recognition; slope = -0.16; p = 0.04; 95% CI: -0.31, -0.01). There was also a significant improvement in scores for females on the GCI (with LEL and UEL), the PLS total score (UEL) and the W-J Applied Problem subtest (UEL).
Among the 587 women with complete dental and covariate data, 78 had one or more amalgam surfaces placed during pregnancy, and 76 had at least one occlusal point placed during pregnancy. Placement of amalgam surfaces or occlusal points during pregnancy did not significantly predict any outcome after adjusting for other model covariates and exposures (data not shown).
In the primary analysis that included 48 models we found no adverse association between exposure using either surfaces or occlusal point scores and 46 endpoints. There was an adverse association between amalgam points and the W-J Letter Word score. Prenatal Hg0 exposure using our secondary metric, the occlusal point score, showed a significant slope of -0.16 (p = 0.04) in males indicating an adverse association. This finding was present only using the UEL and was present in two models [without (data not shown) and with (Table 5) adjustment for prenatal and recent postnatal MeHg exposure]. There were no other adverse associations between any of the 4 dental amalgam scores and the 6 endpoints either without or with adjustment for MeHg. The UEL carries a higher degree of uncertainty than the LEL since it is derived by including 'possible' restorations. Considering we fit 48 primary models, the presence of two adverse associations could be a chance finding and does not imply that prenatal exposure to Hg0 from dental amalgams results in neurobehavioral consequences. Accumulation of Hg in the fetal brain attributable to maternal inhalation of Hg0 is reported to be significantly less than in the maternal brain.48 This is likely due to 'first pass' oxidation of Hg0 in the fetal liver to divalent mercury (Hg++), which does not cross the blood-brain barrier as well as Hg0.49 However, several studies have found that males are more susceptible to the toxic effects of mercury than females.50,51,52 The two adverse findings in males are therefore intriguing and warrant further prospective investigation.
We found several significant interactions with sex, both using our primary surface metric (Table 4) and our secondary occlusal points metric (Table 5). Most of the significant interactions were with the UEL metric. As the number of prenatal occlusal points increased, females performed significantly better on the GCI (with both LEL and UEL), the PLS Total Score (with the UEL), and the W-J Applied Problems Score (with the UEL), in covariate-adjusted models, with and without adjustment for pre and postnatal MeHg. We know of no scientific reason to believe that maternal amalgam might improve neurodevelopmental outcomes in either sex. Dental care is free in Seychelles and access to services should be equivalent. However, higher SES mothers may place a greater value on regular dental care and optimally utilize restorative services. Although higher SES might favorably influence outcomes, it would not explain the apparent disparity between males and females. The findings could also be spurious.
A compelling reason for examining this cohort of children was to explore whether the risk of adverse neurodevelopmental outcomes was accentuated by co-exposure to MeHg and Hg0. Children in this cohort were exposed prenatally and postnatally to elevated levels of MeHg. Consumption of fish is the primary protein source for inhabitants of the island nation of Seychelles. Mothers in this study reported eating approximately 12 fish meals per week during pregnancy.21 This high level of fish consumption resulted in a mean prenatal MeHg (hair THg) exposure of 6.7 ppm. The children also consumed fish and their recent postnatal MeHg exposure was 6.4 ppm on average. In comparison, the 1999-2000 U.S. NHANES study found a mean exposure (hair THg) of 0.47 ppm in females of child bearing age (16-49 years of age) and postnatal exposure of 0.22 ppm in children aged 1-5 years.53 Compared to the US NHANES, the Seychelles mean prenatal MeHg exposure was 14 times higher and the postnatal exposure was 29 times higher. Our models of prenatal and recent postnatal MeHg exposure in this study (Tables 4 and and5)5) confirm the absence of any detectable adverse influence of prenatal and recent postnatal MeHg exposures, as reported in our earlier analyses of the entire cohort.21
To our knowledge, this is the first study to comprehensively examine the risk of prenatal Hg0 exposure from maternal amalgams. The study's strengths include a large, well-defined cohort, sensitive neurodevelopmental assessments, and the presumption that if adverse effects were present, they may be more readily detectable in subjects with other forms of mercury exposure. Moreover, we utilized two different metrics as biomarkers of Hg0 exposure from amalgam restorations and did find significant associations between covariates known to influence child development and endpoints. This suggests there was sufficient power to detect associations if they were present.
The most significant limitation of this study was its retrospective design. We determined the maternal amalgam status during gestation by examining the mothers 10 years after delivery and then reviewing their past dental records to complete the picture. Although dental records in Seychelles were very good, we adjusted for this uncertainty by utilizing two measures of exposure. The LEL and the UEL represent the most likely 'minimum' and 'maximum' respective numbers of amalgams present in the mother during pregnancy. The true exposure level presumably lies 'bracketed' between these levels. It is most likely closer to the LEL, which represents amalgams with documented presence. Consequently, some amalgam exposures could have been misclassified. In addition, there may have been covariates that were important that were not measured.
We do not consider results of this retrospective study to be definitive and are currently studying developmental outcomes in another cohort of children in which maternal amalgam status during gestation was recorded prospectively.
We carried out a retrospective study of prenatal Hg0 exposure from maternal dental amalgams to determine if there were adverse associations with children's neurodevelopment. We found two adverse associations present only in males after examining two Hg0 exposure measures, six neurodevelopmental endpoints, and 48 models. We do not believe these data support the hypothesis that prenatal exposure to Hg0 from amalgam is harmful to the developing fetus.
We are especially grateful to members of the Oral Health Directorate, Ministry of Health, Seychelles (Elisabeth Arissol, Marie Helene Dogley, Agnes Elizabeth, Helena Elizabeth, Kathleen Ernesta, Dr. Harold Pothin, and Dr. Eric Van Holle). We thank Margaret Langdon for technical assistance.
Funding/Support: This research was supported by National Institute of Environmental Health Sciences (NIEHS) and National Institute of Dental and Craniofacial Research (NIDCR) (ES-15578, ES-05497, ES-01247, and ES-07271), by a grant from the United States Food and Drug Administration (FDA), and by the Ministry of Health (MOH), Victoria, Mahé, Republic of Seychelles.
Gene E. Watson, D.D.S., Ph.D. is an associate professor, Eastman Institute for Oral Health, Department of Environmental Medicine, and Department of Pharmacology and Physiology, University of Rochester, Rochester, NY. He contributed to the study concept and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript, and study supervision.
Miranda Lynch, Ph.D. was a student in the Department of Biostatistics and Computational Biology, University of Rochester, Rochester, NY. She now is a post-doctoral student in the Department of Biostatistics, Harvard School of Public Health, Boston, MA. She contributed to the analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript, and statistical analysis.
Gary J. Myers, M.D. is a professor, Department of Neurology, University of Rochester, Rochester, NY. He contributed to the study concept and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript, and study supervision.
Conrad F. Shamlaye, M.D. is an epidemiologist, Republic of Seychelles Ministry of Health, Victoria, Mahé, Seychelles. He contributed to the study concept and design, acquisition of data, analysis and interpretation of data, critical revision of the manuscript, and study supervision.
Sally W. Thurston, Ph.D. is an associate professor, Department of Biostatistics and Computational Biology, University of Rochester, Rochester, NY. She contributed to the analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript, and statistical analysis.
Grazyna Zareba, Ph.D. is a research assistant professor, Department of Environmental Medicine, University of Rochester, Rochester, NY. She contributed to the acquisition of data, critical revision of the manuscript, and technical support.
Thomas W. Clarkson, Ph.D. is professor emeritus, Department of Environmental Medicine, University of Rochester, Rochester, NY. He contributed to the study concept and design, critical revision of the manuscript, and technical support.
Philip W. Davidson, Ph.D. is a professor, Department of Pediatrics, University of Rochester, Rochester, NY. He contributed to the study concept and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript, and study supervision.
Conflict of Interest Disclosures: The authors declare no conflicts of interest.
PubMed Central Canada is a service of the Canadian Institutes of Health Research (CIHR) working in partnership with the National Research Council's Canada Institute for Scientific and Technical Information in cooperation with the National Center for Biotechnology Information at the U.S. National Library of Medicine(NCBI/NLM). It includes content provided to the PubMed Central International archive by participating publishers.


text:
VIEWS: 5 PAGES: 2 POSTED ON: 2/11/2011 Public Domain
Piano keyboards have allowed both serious and casual musicians to interact with this popular musical instrument. Although there is more to the piano than its keyboard, those black and white keys are the components musicians must touch to bring forth melodies. Tickling the ivories is the method of evoking sound. This instrument is often used to accompany school children in choir and singing performances. It is also utilized by pianists in an array of genres ranging from classical symphonies to jazz and rock and roll. This instrument was formerly called the pianoforte. Pianoforte is an Italian word that translates into loud and soft harpsichord. It is a member of the percussion family of instruments. Other musical families of instruments include the brass family, the woodwind family and the strings. Percussion instruments make music by the striking of one object against the other. Examples of other percussion instruments include the drum, the triangle, xylophone, cymbals and rhythm sticks. The piano 鈥檚 music comes from the striking of a keyboard which then hits internal sound makers within the body of the piano. Specifically, the keyboard causes felt covered hammers to hit steel strings. Each string produces a different vibration of sound. There are also foot pedals which affect the sound, causing it to soften, blur into one another or hold a note. The piano 鈥檚 invention is said to have occurred in Italy around the year 1700. An Italian harpsichord maker named Bartolomeo Cristofori was employed as a keeper of instruments when he constructed the first piano. It wasn 鈥檛 widely accepted initially, but it eventually caught on with composers. One of the earliest composers to use it was Wolfgang Mozart, who wrote many of his operas, concertos and sonatas on it. Johann Sebastian Bach was reportedly not as enamored with the instrument initially, claiming it to be too quiet for his needs. Other composers who wrote for the piano include Haydn, Beethoven, Liszt, Schumann, Brahms, and Chopin. The earliest pianos were different from the modern day versions. The initial instruments were modeled after the harpsichord. They had ranges of very soft sounds all the way to quite loud. The first upright piano was constructed in the late 1700 鈥檚 by an Austrian man named Johann Schmidt. The keys of today 鈥檚 keyboard are predominantly white with black. On a modern model, there are usually a total of 88 keys, 52 white ones and 36 black ones. This isn 鈥檛 always the case, however, as some small studio or 鈥済 ig 鈥?piano keyboards only have a total of 65. These smaller types are lighter weight and therefore easier to tote along to gigs. Some of the earlier models were made up of an opposite compilation, the majority black with some white. Taking piano lessons can be a wonderful addition to a culturally rich childhood. Not only does playing a musical instrument give a child the tools to produce lovely music, but it can also help him or her to develop enhanced mathematics capabilities. It is for this reason that piano keyboards are popular to learn to play. Childhood lessons with piano keyboards in New Orleans can foster a lifelong love of music. To learn more visit http://www.hallpiano.com
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Pablo Sandoval hits three homers against Padres
Sep 4, 2013, 10:18 PM EDT
Pablo Sandoval won't be having any three-homer games in the World Series this October, but he did accomplish the feat for the first time in the regular season Wednesday as the Giants crushed the Padres 13-5.
Sandoval had a modest 10 homers this season before taking three relievers deep tonight. He had a two-run shot off Brad Brach in the fifth, a solo homer off Brad Boxberger in the eighth and then a three-run bomb off Dale Thayer in the ninth.
The homers also gave him his first career six-RBI game.
Sandoval previously hit three homers in Game 1 of the World Series last year against the Tigers. He finished the postseason with six in 66 at-bats. This year, he had just two in 238 at-bats since the beginning of June.
- Chip Caray's Eyebrows - Sep 4, 2013 at 10:55 PM
(Insert fat joke here.)
- temporarilyexiled - Sep 5, 2013 at 8:29 AM
Baby Ruth
- hcf95688 - Sep 5, 2013 at 12:15 AM
Does anyone really give a shit about this game?
- Jonny 5 - Sep 5, 2013 at 6:30 AM
Performance enhancing donuts are ruining baseball these days.
- ctony1216 - Sep 5, 2013 at 8:09 AM
More like performance-enhancing quinoa. Pablo's been on a diet:
"If San Francisco Giants third baseman Pablo Sandoval is looking a little slimmer these days, it's because he has a culinary ally helping him – his older brother Luis, who has been traveling with the player and preparing his meals. Sandoval, dubbed "Kung Fu Panda" for his ample physique, has dropped more than 20 pounds in the past month and a half."
- yahmule - Sep 5, 2013 at 1:20 PM
20 pounds off Pablo is like throwing a deck chair off the Titanic. The fried plantains will be back with a vengeance, also with extra sour cream and sugar.
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RoxyStriple RoxyStriple is offline
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|15:24 - RoxyStriple quoted TL2Bass in post Maybe the Street Triple 800 isnt going to be a good thing...thoughts?
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STL250 Cake located outside main entrance
This is your Eagle Watching Headquarters. View a live bald eagle on select Saturdays in January. Pick up information on dining, loding, shopping, events and the best places to see the eagles.
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Why does Eric Holder still have a job?
As Ryan Lizza just said on CNN, the Obama Administration "crossed a line that had never before been crossed" — … Continue reading Why does Eric Holder still have a job?
"Life is a state of mind"
As Ryan Lizza just said on CNN, the Obama Administration "crossed a line that had never before been crossed" — … Continue reading Why does Eric Holder still have a job?
Rush Limbaugh blames the struggles of Oprah's TV network on her "association with Obama" (and throws in some trademark race-baiting). …
I'll concede much of the press was pulling for Obama in 2008. But to contend, as many conservatives do, that the president received a free pass from the media doesn't stand up to scrutiny.
Though I'm glad the president has completed his evolution (more on that later) don't expect to see me popping any … Continue reading I'd rather be single
Some conservatives will go to great lengths to recycle ridiculous conspiracies, such as the one that claims Obama hates honkies. … Continue reading Obama's silence on death of George 'Goober' Lindsey speaks volumes
Hell, Michael McDonald is cool compared to Mitt Romney.
US President Barack Obama on Monday challenged the "unelected" Supreme Court not to take the "extraordinary" and "unprecedented" step of … Continue reading Obama mimics Limbaugh
The worst-case scenario is unfolding in Egypt, where the Muslim Brotherhood has broken its pledge not to seek the presidency. … Continue reading Fundamentalists never tolerate moderation
President Obama has been criticized for rarely engaging the county on matters of race but, seeing the nasty reaction from … Continue reading The real dividers
The owner of the company that produces the disquietingly popular anti-Obama bumper sticker — "Don't Re-Nig in 2012″ — denies … Continue reading Someone buy this racist a dictionary
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While it's convenient for the left to ostracize a region they view as foreign, racism is not the sole provence … Continue reading Reports of racism's death have been greatly exaggerated
Just saw Peter Orszag, Obama's former OMB director, claim the White House abandoned the Simpson-Bowles plan because it had no … Continue reading The WH's false narrative on Simpson-Bowles


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Get all the scoop on TODAY 8/3 - 8/9, airing on NBC (more...)
Get all the scoop on WATCH WHAT HAPPENS LIVE! , airing on BRAVO (more...)
Loinsgate has released a new trailer for their upcoming action/comedy film AMERICAN ULTRA. The film stars Jesse Eisenberg and Kristen Stewart. Get a first look below! (more...)
Get all the scoop on WATCH WHAT HAPPENS LIVE! 8/2 - 8/13, airing on BRAVO (more...)
Loinsgate has released a new clip from their upcoming action/comedy film AMERICAN ULTRA. The film stars Jesse Eisenberg and Kristen Stewart. (more...)
Bolstering its primetime programming portfolio, AXS TV has entered into a multi-year licensing agreement with the Disney-ABC Television Group for off-network cable rights to the first three seasons of the critically-acclaimed primetime ABC drama, NASHVILLE. (more...)
Get all the scoop on THE LATE LATE SHOW WITH JAMES CORDEN, airing on CBS for the week of June 29, 2015! (more...)
Molly Shannon, Thomas Mann, and Nick Offerman star in the new drama-comedy, ME AND EARL AND THE DYING GIRL. (more...)
Actress Connie Britton, Thomas Mann, Olivia Cooke and RJ Cycle star in the new movie "Me and Earl and the Dying Girl." (more...)
Get all the scoop on TODAY 6/8 - 6/14, airing on NBC (more...)
"Nashville" star Connie Britton stopped by CBS's THE TALK to discuss her award-winning new film "Me and Earl and the Dying Girl!" (more...)
Guy Pearce and 'Nashville's Connie Britton stopped by last night's LATE LATE SHOW with JAMES CORDEN on CBS. Watch all the clips from the apperance below! (more...)
Get all the scoop on THE LATE LATE SHOW WITH JAMES CORDEN, airing on CBS for the week of June 1, 2015! (more...)
Fans will be able to see ABC's 'Nashville' stars LIVE at The Ridgefield Playhouse on Friday, June 26, at 8 p.m. Actors Charles Esten and Clare Bowen have plenty of experience making music on the stage and screen, Esten had a long-running stint at the start of his career playing Buddy Holly in the West End, while Bowen appeared in Spring Awakening in her native Australia. So it's no coincidence that they play singer-songwriters on the nighttime soap about the lives and loves of country musicians. Esten and Bowen have been writing and singing for a long time, and, thanks to the launching pad that 'Nashville' has provided, they've been scoring slots at the Stagecoach festival and opening gigs for artists such as Alan Jackson and Dierks Bentley. The Ancient Mariner will make it a great night out by pouring a complimentary glass of wine with dinner before the show when tickets are presented. This event is part of the Northeast Builders LLC Country Series with media sponsor Country 92.5fm. (more...)
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ABC continues its commitment to great storytelling with the announcement of its 2015-16 slate of programming, including the addition of 10 new series. Paul Lee, president, ABC Entertainment Group, will unveil the network's new lineup to the advertising and media communities this afternoon at Lincoln Center's Avery Fisher Hall. (more...)
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text:
Aldebaran, who finished third in the June 14 Stephen Foster Handicap (gr. I) at Churchill Downs, will shorten up from that race's nine-furlong distance when he competes in Friday's seven-furlong Tom Fool Handicap at Belmont.Trainer Kiaran McLaughlin, who will saddle Northern Rock for Friday's Tom Fool Handicap (gr. II), hopes the gelding gives the trainer his first stakes victory at Belmont this meet. McLaughlin is certainly doing well this season--more than half of his starters have won their races--but he hasn't entered a horse in added-money company yet. He'll have to face Aldebaran and six other contenders first. In his last start Aldebaran finished third in the nine-furlong Stephen Foster Handicap (gr. I). Before that, he won the grade I Met Mile.The field for Friday's grade II, $150,000 Tom Fool Handicap, from the rail out:PP, horse, trainer, jockey, weight
1--Ginzano, Allen Iwinski, Jose Santos, 112
2--Najran, Nick Zito, Edgar Prado, 116
3--Vodka, John Hertler, Heberto Castillo Jr. 113
4--Northern Rock, Kiaran McLaughlin Richard Migliore 114
5--Aldebaran, Bobby Frankel, Jerry Bailey, 122
6--State City, Tom Albertrani, Jorge Chavez, 118
7--Voodoo, Jimmy Jerkens, John Velazquez, 114
8--Peeping Tom, Patrick Reynolds, Shaun Bridgmohan 117
Aldebaran Returns in Tom Fool on Home Turf
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Silver Spoon Restaurant
Local breakfast and lunch restaurant, the one that is in every town!
73 Main Street, Eastampton, MA 01027
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We demonstrate a high-efficiency optical modulator at ~1323 nm using the quantum Zeno effect in a ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam while the upper leg of the transitions represents the signal beam. The cross-modulation of the signal beam transmission is observed as the control beam is intensity modulated, and is explained in terms of the quantum Zeno effect. We observe a modulation depth of near 100% at frequencies up to 1MHz and demonstrate modulation at speeds up to 75 MHz, with a 3 dB bandwidth of about 5 MHz, limited by the homogeneous linewidth of the intermediate state. We also describe how much higher modulation speeds could be realized by using a buffer gas to broaden the transitions. We identify and explain the special conditions needed for optimizing the modulation efficiency. Numerical simulations of modulation at ~1GHz are presented. The maximum modulation speed is found to scale with the pressure-broadened linewidth of the intermediate state, so that much higher speeds should be attainable.
1. Introduction
All-optical modulation and switching are important for optical communication and quantum information processing [1–5]. Conventional techniques of non-linear optics typically require relatively high power, and are not well suited for these applications. An ultra-low power quantum Zeno effect based optical modulator using a degenerate V-system and a tapered nano fiber embedded in Rb vapor has recently been demonstrated by us [6]. Unfortunately, this is not useful for switching optical fields in the telecommunication band. On the other hand, the ladder type Zeno modulator described here can be used to modulate signals at 1323 nm, using a control beam at 795 nm. In combination with a tapered nano fiber (TNF) setup [6–9], this modulator can be used to produce an optical modulator at extremely low powers of the control beam (~40nW). The TNF-based modulator could also be integrated with other applications of TNF such as super-continuum generation [10], coupling light into micro-sphere resonators [11,12], near-field sensing [13,14], investigation of interaction of evanescent field with cold atoms [15–17], and exploration of opto-mechanical effects [18,19].
2. The quantum Zeno effect in a ladder transition
The quantum Zeno effect (QZE) [20–22] refers in general to the suppressed evolution of a quantum state through the quantum measurement process. However, in all instances, the QZE can be interpreted more transparently in terms of AC-Stark shifts or splitting, without invoking the concept of measurement explicitly [6]. Using this approach, the basic mechanism of the degenerate V-system Zeno switch has been explained in terms of the QZE [6]. Specifically, in [6], the QZE was shown to be a manifestation of the AC-Stark splitting of dressed states. A similar interpretation also holds when a three level system involving a ladder type transition is used. As shown in Fig. 1(a) , the system consists of three states: a ground state (|1>), a strongly-damped intermediate state (|2>), and a third state (|3>) which may or may not be strongly damped. The control beam couples |1> to |2>, and the probe beam couples |2> to |3>. For resonant excitation, the corresponding dressed states (defined as products of photon number states and atomic states) are degenerate, as shown in Fig. 1(b). When the coupling between |1> and |2> is strong, the resulting states, upon diagonalization (| + > and |->) are split by an amount equaling the Rabi frequency of the |1> to |2> transition, which is much larger than the natural linewidth of |2>, as illustrated in Fig. 1(c).
Fig. 1
There are several combinations of parameters that can be considered for controlling the probe absorption. Consider first Case I, where the probe is resonant for the |2> to |3> transition, but the pump is relatively weak, so that the two diagonalized states (| + > and |->) are not resolved. In this case, the probe is transparent when the pump is not present (since the atoms remain in state |1>), and is absorbed when the pump is turned on. Consider next Case II where the pump is strong so that the two diagonalized states are clearly resolved, but the probe is detuned from the |2> to |3> transition (positively or negatively) by half the separation between the two diagonalized states. In this case, the probe is absorbed in the presence of the pump, but is transparent when the pump is not present. This is the same as what happens for Case I, but for different reasons. Finally, consider Case III, where again the pump is strong so that the two diagonalized states are clearly resolved, but the probe is resonant for the |2> to |3> transition (as shown in Fig. 1). In this case, the probe is transparent both in the presence and in the absence of the pump. Cases I and II can be considered to be QZE-based control of probe absorption, since the mechanism in each case can be interpreted in terms of AC-Stark effects. In this paper, we describe experimental results based on Case I, while the scheme we describe for high speed modulation in the presence of buffer gas is based on Case II.
3. Experimental set-up
In this section, we describe our experiment for realizing a Case I type QZE modulator in a conventional vapor cell of length ~7.5cm, under free space propagation of light. The experimental configuration is illustrated schematically in Fig. 2 . Briefly, beams from two tunable lasers (a Ti-Sapphire laser at 795 nm, and a fiber laser at 1323 nm) are combined with a dichroic mirror (DCM). Both the control and the signal beams are co-propagating, and linearly polarized in the same direction. A part of the 795 light is sent to a reference vapor cell for saturated absorption spectroscopy and locking. The combined beams are sent through a vapor cell, shielded from magnetic fields with μ-metal. After passing through the cell, another DCM is used to split the light into two parts, and the signal at each frequency is monitored with a separate detector. The cell is heated to temperatures of about 150° C using bifilarly wounded wires that do not add any magnetic fields. For 85Rb we estimated experimentally the optical depth for the strongest transition (5S1/2,F = 3,mF = 3 to 5P3/2,F = 4,mF = 4) on the D2 line to be ~220, corresponding to an atomic density of ~1010 cm−3. For 87Rb the optical density for the strongest transition (5S1/2, F = 2, mF = 2 to 5P3/2, F = 3, mF = 3) on the D2 line was estimated to be ~85, corresponding to an atomic density of ~3.8*109 cm−3.
Fig. 2
The acousto-optic modulator (AOM) and the electro-optic modulator (EOM) shown in Fig. 2 are used only while performing the actual modulation, and are removed while characterizing the absorption profile at 1323nm. While performing spectroscopic measurements and switching at low frequencies (up to ~5MHz), we used Thorlabs PDA55 (Silicon) and Thorlabs PDA400 (InGaAs) for detecting light at 795nm and 1323nm respectively. For high frequency switching, a fast APD (New Focus 1647) with a bandwidth of 1 GHz was used for detection of 1323nm light.
4. Spectroscopic details
We chose to use the 5S1/2 →5P1/2→6S1/2 ladder transition in Rb for our experiment, dictated in part by lasers readily available to us. Using the reference saturated absorption cell, we locked the pump laser (795 nm) to one of the resonances of the 5S1/2 →5P1/2 manifold and the probe laser (at 1323nm) was then scanned across the 6S1/2 manifold over a few GHz. The modulator should work just as well if the ladder transition is of the type 5S1/2 →X→Y, where X is 5P1/2 or 5P3/2, and Y can be one of many states that are coupled to the X states via optical dipole transitions and have higher energies than that of X. For example Y can be 7S1/2, 4D3/2, 4D5/2, 5D3/2, 5D5/2, and so on.
Figure 3(a) shows the spectroscopic details of the ladder transition for 85Rb. The probe beam was scanned over the 6S1/2 manifold while the control beam was locked to the F = 2→F = 2 transition on the lower leg. The separation between the hyperfine levels in the 5P1/2 manifold (~360 MHz) is less than the Doppler linewidth (~600 MHz). Hence, atoms are excited to both hyperfine levels of the 5P1/2 manifold even if the 795nm laser is locked to only the F = 2 →F = 2 transition. As a result, it is expected that 4 lines would be observed for the 1323nm absorption (upper leg) as this laser is scanned over a few GHz (Fig. 3(b)). However, it is to be noted that, due to Doppler shift, the atoms excited to the F = 3 state of the intermediate level correspond to negative velocity (with respect to the direction of propagation of the 795 nm laser beam) atoms, and not zero velocity atoms. Thus, the transitions from this state to the 6S1/2 manifold are shifted to lower frequencies by an amount equal to the separation between the hyperfine states in the 5P1/2 manifold (~360 MHz). In the case of 85Rb, the frequency difference between the hyperfine states in the 6S1/2 manifold (~710 MHz) is such that this shift causes the F = 2→F = 2 transition almost to overlap the F = 3→F = 3 transition, for the 1323 nm beam. As a result, only 3 lines are expected to be observed distinctly (see Fig. 3(c)). It is to be noted that Figs. 3(b) and 3(c) only illustrate the expected relative positions of the 85Rb absorption lines (at 1323nm), and not the actual observed data, which are described next.
Fig. 3
Figures 4(a) and 4(b) show a couple of typical profiles that were observed for 85Rb. The data in Fig. 4(a) corresponds to a relatively low power (~2 mW) of the control beam, and only three absorption lines are observed, in keeping with the explanation provided in Fig. 3 above. The relative separation between the lines is in good agreement with the expected spectrum, as illustrated in Fig. 3(c). This data has been taken in AC mode (on a standard digital oscilloscope) and hence shows negative values. The slow background modulation seen in the signal is most likely due to the etalon effect from the windows of the cell. The data in Fig. 4(b), taken in DC mode, corresponds to much higher power (~200 mW) of the control beam, and we see almost complete absorption of the probe while the lines are strongly power broadened. Of course, the amount of 1323nm absorption increases with the number of atoms excited to the intermediate leg, which in turn is determined by the power of the control beam. Thus at sufficiently high power of the control beam, the upper transition is completely saturated. It should be noted that even in this case, the pump power is not high enough to correspond to Case II, since the power broadening is less than the effective width of the intermediate state (~600 MHz) due to Doppler broadening.
Fig. 4
Figure 5 shows the spectroscopic details for 87Rb and a few typical absorption profiles that were observed at 1323nm. The control laser was locked to the F = 1→F = 1 transition on the lower leg, as shown in Fig. 5(a). For moderately high powers (~50mW) of the control beam, atoms get excited to both hyperfine levels of the 5P1/2 manifold, due to power broadening of the 5S1/ 2 → 5P1/2 transition. At these powers, we can clearly resolve 4 absorption lines, as shown in Fig. 5(b). It is worth noting that each of the lines is control-power-broadened because of the fact that a significant number of velocity groups are excited to both hyperfine states of the intermediate level due to the relatively high power of the control beam. At sufficiently low powers of the control beam (~0.5mW), two of the four lines are almost completely suppressed, and each individual line can be seen as a narrow sharp line, as illustrated in Fig. 5(c).
Fig. 5
As before, the data in Fig. 5(b) and Fig. 5(c) have been taken in AC mode on a standard digital oscilloscope, and hence show negative values. The slow background modulation observed in both figures is again most likely due to the etalon effect of the Rb cell window, as mentioned previously.
It should be noted that ladder transitions of this type have been studied previously, theoretically as well as experimentally [23–25], in different contexts. The Doppler-free nature of the upper leg of the ladder transition in the co-propagating configuration is consistent with the theoretical model presented in [25], and the experimental results presented in [24,25]. The hyperfine splitting frequencies we have observed for the 5P1/2 to 6S1/2 transition for both 85Rb and 87Rb are in agreement with those reported in [23]. However, the experiment reported in [23] did not show any absorption lines for this transition; therefore, a quantitative comparison of the spectral response is not possible. Finally, the accidental near-degeneracy we have observed between the F = 3↔F = 2 and F = 2↔F = 2 transitions on the upper leg in the case of 85Rb due to contributions from different velocity groups (as illustrated in Fig. 3(c) and Fig. 4(a)) has not been reported in any of these references.
5. Modulation
In order to demonstrate modulation, we chose to use the strongest absorption line at the upper leg of transitions, which in our case was the F = 3 →F = 2 resonance for 85Rb (due in part to the fact that in a natural mixture of Rb, 72.15% is 85Rb, and 27.85% is 87Rb). Keeping the probe laser (1323 nm) parked on this resonance, we then modulated the amplitude of the pump beam (795 nm). At low frequencies, switching of the control beam was accomplished using an AOM while for higher frequencies, an EOM configured for intensity modulation was used. The result is shown in Fig. 6 .
Fig. 6
For low frequencies, we used a pump power of ~200mW and we see a strong modulation, in phase with the pump modulation, with a modulation depth of essentially 100% up to a speed of 1MHz. The modulation depths obtained while using the EOM were smaller because of the low control beam power (~2mW) used. This was necessitated by the damage threshold (~20mW) of the EOM used to switch the pump beam and the relatively low efficiency of the EOM (~20%). We have tested the modulation up to a speed of 75 MHz, and determined a 3dB bandwidth of approximately 5 MHz, as shown in Fig. 7 . In Fig. 7, we have plotted the modulation amplitude at various frequencies (obtained using the EOM), normalized to the amplitude at 1MHz, where the modulation depth was essentially 100%, when obtained with the AOM.
Fig. 7
A careful consideration of the physical mechanism behind this modulation reveals that the modulation speed is fundamentally limited by the time needed for the atoms to repopulate the ground state, after the pump is turned off, so that they can absorb the probe again. This means that the modulation bandwidth cannot exceed the homogeneous linewidth (HL). This constraint is rather obvious for Case I, which has been employed here. As we will discuss later, this constraint on the maximum speed also holds if Case II is employed for modulation.
6. High speed modulation – proposed experiment and simulation results
6.1 Proposed experiment
The HL can be increased very significantly by adding a buffer gas, such as 4He. In a series of studies carried out in the context of the development of diode pumped alkali lasers (DPALs) [26], it has been shown that the atoms excited to the 5P3/2 state relaxes very rapidly to the 5P1/2 state.
This process increases the HL for the pump transition significantly. For example, HL (given effectively by γdown, which is much larger than γ21) is about 10 GHz for a buffer gas pressure of 1 atm, and can be as large as 500 GHz for a pressure of 25 atm. However, the rate of decay from the 5P1/2 state to the ground state is not affected by the presence of the buffer gas, thus preventing rapid repopulation of the ground state. This effect would normally limit the maximum modulation speed achievable. But, this constraint can be circumvented via the addition of an auxiliary beam (which we henceforth call the deshelving beam) that would be turned on at the same time as the pump is turned off, and turned off before turning on the pump again, as illustrated in Fig. 8 . For best performance, (in terms of contrast obtained during modulation) the pulse width of the de-shelving beam applied should be much smaller than the time scale of the dominant relaxation rate (namely 1/γup) from the 5P1/2 state. However, even for longer pulse widths (up to 100/γup), the system produces very good contrast. Furthermore, this beam should be as close as possible to an ideal π-pulse in a 2-level system. The de-shelving beam causes rapid repopulation of the ground state, thereby ensuring atoms can be cycled back to the 5P3/2 state when the pump is turned on again. The speed would be limited by the dominant relaxation rate (γdown) of the 5P3/2 state, which is in turn controlled by the buffer gas pressure. It is to be noted that while we have chosen to use 6S1/2 as the highest level to illustrate this scheme, there are many other states (e.g., 7S1/2, 4D3/2, 4D5/2, 5D3/2, 5D5/2 and so on) that would work just as well. However, for optimal operation, the intermediate state must be 5P3/2, since the quenching rate is higher from 5P3/2 to 5P1/2 than that in the reverse direction.
Fig. 8
6.2 Simulation results
Preliminary results obtained from the simulation of the system shown in Fig. 8 are presented in Fig. 9 . The values of the decay rates used were γdown ~10 GHz, γup ~2.5 GHz, γ34 = γ32 ~3 MHz and γ21 = γ41 ~6 MHz. The simulations are carried out using the Case II configuration, with the negative probe detuning matched to half the Rabi frequency. Thus, the probe is resonant with the | + > to |3> transition. The residual oscillations seen in the probe absorption occur at the pump Rabi frequency.
Fig. 9
These oscillations can be understood clearly by considering the limiting case where state |2> is completely undamped (γdown = 0, γ21 = 0), state |3> decays to state |2> only, and the deshelving beam is turned off, so that state |4> is completely decoupled from the system. In this case, the population of level |2> oscillates between 0 and 1 (in the limit of a vanishingly weak probe beam) at the rate of the pump Rabi frequency. Thus, if the configuration of Case I is employed, the probe absorption would obviously oscillate (between the maximum value and zero) at the same frequency. Oscillation of the probe absorption between the maximum value and zero also occurs if Case II is employed. The later may appear to be somewhat surprising, since the population of the | + > level (as well as that of the |-> level) remains constant at a value of 1/2, and the probe is resonant with | + > to |3> transition. On the other hand, it is sensible if one considers the fact that at some point in time there are no atoms in state |2>. These two observations can be reconciled by noting that even though the probe is resonant with the | + > to |3> transition, there is also the off-resonant transition between the |-> state and state |3>. For the very short time scale of the Rabi oscillation, the | + > and |-> state are effectively broadened by the Rabi frequency (akin to transit time broadening), in a manner so that during one point in the Rabi oscillation cycle, the imaginary part of ρ32, which determines the probe absorption (ρ being the density matrix) vanishes due to equal and opposite contributions from the | + > and |-> states. We have verified this explicitly, using numerical simulations under this condition.
In the presence of the strong damping of level |2>, as employed in the simulation for Fig. 9, these oscillations get damped, producing a steady-state absorption of the probe, on a time scale given by the damping rate of level |2>. Thus, if we used the same technique, but without the buffer gas, the probe absorption would remain oscillatory through the whole time during which the pump is on, since the timescale for reaching steady state would be given by the inverse of the radiative decay rate (γ21) of level 2 only, corresponding to more than 30 nanosecond, which is much longer than the modulation rate shown in Fig. 9. Thus, employing Case II by itself is not enough to achieve high speed modulation; the rapid decay rate of level |2> is essential.
In Fig. 10 , we show results obtained for the same set of parameters as used in Fig. 9, except that the deshelving beam is not used. As can be seen, a modulation with a significant contrast is still achievable. Thus, the presence of the deshelving beam is not essential for obtaining high speed modulation. To see why this is the case, we recall from Fig. 8 that there is also a relaxation (γup) of atoms from the 5P1/2 state to the 5P3/2 state in the presence of buffer gas, at a rate which is about 4 times smaller than the decay rate (γdown) in the opposite direction. Consequently, the atoms never leave the 5P3/2 state completely during the time when the pump is turned off. Half of these atoms get tuned back to resonance (between the | + > and |3> states) when the pump is turned back on, producing strong absorption. The reduced contrast in the absence of the deshelving beam is due to the fact that fewer number of atoms in state |2> decay to state |4> because there is no mechanism for atoms in state |4> to be transferred to state |1>. In the presence of the deshelving beam, the number of atoms remaining in state |2> after the deshelving π-pulse is significantly smaller, thus producing higher transparency for the probe, and consequently higher modulation contrast.
Fig. 10
For both cases (deshelving beam on or off), the modulation depth remains virtually uniform for increasing modulation speeds, but the rapid oscillations do not die off at higher speeds. In order to estimate the bandwidth of the modulator, we used the criterion that both the on and off states of the probe must reach a steady state value before the corresponding states of the pump. This gives a bandwidth of about 1.5 GHz for γdown = 10GHz. The bandwidth can be increased further by increasing the value of γdown (as well as γup = γdown/4) and scaling the pump power by the same factor. Indeed, preliminary simulation results have shown that the bandwidth roughly scales with γdown. More details about the impact of various parameters, such as pump and auxiliary beam powers, pulse-width of the de-shelving beam, and the decay rates, on the modulator performance in terms of modulation depth and bandwidth will be presented in a separate paper. Efforts are also underway in our laboratory to investigate the feasibility of realizing a buffer-gas augmented modulator of this type.
It should be possible to realize this scheme in a tapered nano fiber (TNF) set-up, yielding an efficient modulator at the telecom wavelength at very low control powers. The TNF will be designed to operate as a single mode fiber for all three wavelengths: 780 nm, 795 nm and 1323 nm. We have carried out designs of such a TNF, and have shown that there is a range of taper diameters for which it is possible to have a significant overlap between the evanescent modes at these three wavelengths. The TNF would be embedded in a Rb vapor cell, of the type reported in [7], and pressurized with a 4He buffer gas at ~3 atm. The pump and the auxiliary beams will be orthogonally polarized, and combined with a polarizing beam splitter. The probe will be combined with these beams using a dichroic mirror. The combined beams will be launched into the TNF. Similar techniques will be used to separate the probe from the other beams at the output. Of course, the intensity needed to saturate a 500 GHz broadening would be too hard to realize in a TNF. However, based on a typical DPAL laser employing Rb, which requires a threshold pump intensity of about 15 μW/μm2, we estimate that a pump power of about 3 μW should be enough to achieve a few GHz modulation bandwidth in the TNF, which has a mode area of only 0.2 μm2.
7. Conclusion
We have demonstrated a high-efficiency optical modulator at ~1323 nm using the quantum Zeno effect in a ladder transition in a Rb vapor cell. We observe cross-modulation of the signal beam transmission as the control beam is intensity modulated. We obtain a 3dB bandwidth of approximately 5 MHz, which can be improved to a few GHz by using buffer gas to enhance the homogenous broadening. The bandwidth can be controlled by the relaxation rates between the 5P1/2 and 5P3/2 states, which in turn are controlled by the buffer gas pressure. It should be possible to realize this scheme in a tapered nano fiber set-up, yielding an efficient modulator at the telecom wavelength at very low control powers.
This work was supported in part by AFOSR Grant # FA9550-10-01-0228, and the DARPA ZOE program under Grant # W31P4Q-09-1-0014.
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