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Laser scanning is the controlled deflection of laser beams, visible or invisible.Gerald F. Marshall Handbook of Optical and Laser Scanning, Marcel Dekker, Inc., 2004, Scanned laser beams are used in some 3-D printers, in rapid prototyping, in machines for material processing, in laser engraving machines, in ophthalmological laser systems for the treatment of presbyopia, in confocal microscopy, in , in , in Laser TV, and in . Applications specific to mapping and 3D object reconstruction are known as 3D laser scanner.
In order to position a laser beam in two dimensions, it is possible either to rotate one mirror along two axes - used mainly for slow scanning systems - or to reflect the laser beam onto two closely spaced mirrors that are mounted on orthogonal axes. Each of the two flat or polygon (polygonal) mirrors is then driven by a galvanometer or by an electric motor respectively. Two-dimensional systems are essential for most applications in material processing, confocal microscopy, and medical science. Some applications require positioning the focus of a laser beam in three dimensions. This is achieved by a servo-controlled lens system, usually called a 'focus shifter' or 'z-shifter'. Many laser scanners further allow changing the laser intensity.
In laser projectors for laser TV or laser displays, the three fundamental colors - red, blue, and green - are combined in a single beam and then reflected together with two mirrors.
The most common way to move mirrors is, as mentioned, the use of an electric motor or of a galvanometer. However, piezoelectricity or magnetostriction are alternative options. They offer higher achievable angular speeds, but often at the expense of smaller achievable maximum angles. There are also , which are MEMS devices containing a small (millimeter) mirror that has controllable tilt in one or two dimensions; these are used in pico projectors.
When two are moved or rotated against each other, a laser beam can be scanned in a way similar to mirror scanners.
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 Interior design, and in archaeology.
The ability of lasers to harden liquid polymers, together with laser scanners, is used in rapid prototyping, the ability to melt polymers and metals is, with laser scanners, to produce parts by laser sintering or laser melting.
The principle that is used for all these applications is the same: software that runs on a PC or an embedded system and that controls the complete process is connected with a scanner card. That card converts the received vector data to movement information which is sent to the scanhead. This scanhead consists of two mirrors that are able to deflect the laser beam in one level (X- and Y-coordinate). The third dimension is - if necessary - realized by a specific optic that is able to move the laser's focal point in the depth-direction (Z-axis).
Scanning the laser focus in the third spatial dimension is needed for some special applications like the laser scribing of curved surfaces or for in-glass-marking where the laser has to influence the material at specific positions within it. For these cases it is important that the laser has as small a focal point as possible.
For enhanced laser scanning applications and/or high material throughput during production, scanning systems with more than one scanhead are used. Here the software has to control what is done exactly within such a multihead application: it is possible that all available heads have to mark the same to finish processing faster or that the heads mark one single job in parallel where every scanhead performs a part of the job in case of large working areas.
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