angular speeds, but often at the expense of smaller achievable maximum angles. There are also microscanners, which are MEMS devices containing a small (millimeter) mirror that has controllable tilt in one or two dimensions; these are used in pico projectors. Scanning refractive optics When two Risley prisms are rotated against each other, a beam of light can be scanned at will inside a cone. Such scanners are used for tracking missiles. When two optical lenses are moved or rotated against each other, a laser beam can be scanned in a way similar to mirror scanners. Material effects Some special laser scanners use, instead of moving mirrors, acousto-optic deflectors or electro-optic deflectors. These mechanisms allow the highest scanning frequencies possible so far. They are used, for example, in laser TV systems. On the other hand, these systems are also much more expensive than mirror scanning systems. Phased array scanning Research is going on to achieve scanning of laser beams through phased arrays. This method is used to scan radar beams without moving parts. With the use of Vertical-cavity surface-emitting laser (VCSELs), it might be possible to realize fast laser scanners in the foreseeable future. Applications 3D object scanning Within the field of 3D object scanning, laser scanning (also known as lidar) combines controlled steering of laser beams with a laser rangefinder. By taking a distance measurement at every direction the scanner rapidly captures the surface shape of objects, buildings and landscapes. Construction of a full 3D model involves combining multiple surface models obtained from different viewing angles, or the admixing of other known constraints. Small objects can be placed on a revolving pedestal, in a technique akin to photogrammetry. 3D object scanning allows enhancing the design process, speeds up and reduces data collection errors, saves time and money, and thus makes it an attractive alternative to traditional data collection techniques. 3D scanning is also used for mobile mapping, surveying, scanning of buildings and building interiors, and in archaeology. Material processing Depending on the power of the laser, its influence on a working piece differs: lower power values are used for laser engraving and laser ablation, where material is partially removed by the laser. With higher powers the material becomes fluid and laser welding can be realized, or if the power is high enough to remove the material completely, then laser cutting can be performed. Modern lasers can cut steel blocks with