Laser scanning Material effects

Laser scanning is the controlled deflection of a visible or invisible laser beam.Scanning laser beams are used in some 3D printers, rapid prototyping, materials processing machines, laser engraving machines, ophthalmic laser systems for the treatment of presbyopia, confocal microscopes, laser printers, laser shows, laser televisions, and barcode scanners.An application specific to mapping and 3D object reconstruction is called a 3D laser scanner.

Technology

Scanning mirrors: 

Most laser scanners use movable mirrors to steer the laser beam.The steering of the beam can be one-dimensional, as in a laser printer, or two-dimensional, as in a laser show system.In addition, mirrors can cause periodic motion as in barcode scanners or rotating polygonal mirrors in so-called resonant galvanometer scanners or freely addressable motion, as in servo-controlled galvanometer scanners.People also use the terms raster scan and vector scan to differentiate between the two cases.To control the scanning motion, the scanner requires a rotary encoder and control electronics to supply the appropriate current to a motor (for polygon mirrors) or a galvanometer (also called a galvanometer) for the desired angle or phase.A software system usually controls the scanning motion and, if 3D scanning is implemented,the collection of measurement data.To position the laser beam in two dimensions,one mirror can be rotated along two axes mainly used in slow scanning systems or the laser beam can be reflected onto two closely spaced mirrors mounted on orthogonal axes.Each of the two planar or polygonal (polygonal) mirrors is then driven by a galvanometer or electric motor respectively.2D systems are essential for most applications in materials processing, confocal microscopy, and medical science.Some applications require positioning the focal point of the laser beam in three dimensions.This is accomplished by a servo-controlled lens system, often referred to as a "focus shifter" or "z-shifter". Many laser scanners also allow varying laser intensity.In laser projectors used in laser TVs or laser displays,the three basic colors-red, blue and green-are combined into a beam of light that is then reflected together by two mirrors.As mentioned earlier, the most common ways to move a mirror is with an electric motor or a galvanometer.However, piezoelectric or magnetostrictive actuators are alternatives.They provide higher achievable angular velocities,but usually at the expense of a smaller achievable maximum angle.There are also microscanners, which are MEMS devices containing a small (millimeter) mirror with a controllable tilt in one or two dimensions; these are used in microprojectors.

Scanning refractive optics

When two Risley prisms are rotated relative to each other, a beam of light can be randomly scanned within a cone.This scanner is used to track missiles.When two optical lenses are moved or rotated relative to each other, the laser beam can be scanned in a manner similar to a mirror scanner.

Material effects

Some special laser scanners use acousto-optic deflectors or electro-optic deflectors instead of moving mirrors.These mechanisms allow the highest scanning frequencies possible so far.For example, they are used in laser TV systems. On the other hand, these systems are also much more expensive than mirror scanning systems.

Phased array scanning

Scanning of laser beams by means of phased arrays is being investigated.This method is used to scan the radar beam without moving parts. Fast laser scanners will be possible in the foreseeable future through the use of vertical-cavity surface-emitting lasers (VCSELs).