Laser scanning is the controlled
deflection
Deflection or deflexion may refer to:
Board games
* Deflection (chess), a tactic that forces an opposing chess piece to leave a square
* Khet (game), formerly ''Deflexion'', an Egyptian-themed chess-like game using lasers
Mechanics
* Deflection ...
of
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
beams, visible or invisible.
Scanned laser beams are used in some
3-D printers, in
rapid prototyping
Rapid prototyping is a group of techniques used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer aided design (CAD) data.
Construction of the part or assembly is usually done using 3D printin ...
, in machines for material processing, in
laser engraving
Laser engraving is the practice of using lasers to engrave an object. Laser marking, on the other hand, is a broader category of methods to leave marks on an object, which in some cases, also includes color change due to chemical/molecular alte ...
machines, in ophthalmological laser systems for the treatment of
presbyopia
Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness (or age-related long si ...
, in
confocal microscopy
Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser confocal scanning microscopy (LCSM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a sp ...
, in
laser printer
Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively-charged cylinder called a "drum" to d ...
s, in
laser show
A laser lighting display or laser light show involves the use of laser light to entertain an audience. A laser light show may consist only of projected laser beams set to music, or may accompany another form of entertainment, typically mus ...
s, in
Laser TV
Laser color television (laser TV), or laser color video display, is a type of television that utilizes two or more individually modulated optical (laser) rays of different colors to produce a combined spot that is scanned and projected across the ...
, and in
barcode scanner
A barcode reader is an optical scanner that can read printed barcodes, decode the data contained in the barcode to a computer. Like a flatbed scanner, it consists of a light source, a lens and a light sensor for translating optical impulses int ...
s.
Applications specific to mapping and 3D object reconstruction are known as ''
3D laser scanner''.
Technology
Scanning mirrors
![Plexi Galvohalter](https://upload.wikimedia.org/wikipedia/commons/0/0a/Plexi_Galvohalter.jpg)
Most laser scanners use moveable mirrors to steer the laser beam. The steering of the beam can be ''one-dimensional'', as inside a laser printer, or ''two-dimensional'', as in a laser show system. Additionally, the mirrors can lead to a ''periodic'' motion - like the rotating ''polygon mirrror'' in a barcode scanner or so-called ''resonant galvanometer'' scanners - or to a ''freely addressable'' motion, as in servo-controlled
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.
A galvanom ...
scanners. One also uses the terms ''
raster scan
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image s ...
ning'' and ''vector scanning'' to distinguish the two situations. To control the scanning motion, scanners need a
rotary encoder
A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital output signals.
There are two main types of rotary encoder: absolute and increm ...
and control electronics that provide, for a desired angle or phase, the suitable electric current to the motor (for a polygon mirror) or galvanometer (also called
galvos). A software system usually controls the scanning motion and, if 3D scanning is implemented, also the collection of the measured data.
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
An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
or of a
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.
A galvanom ...
. However,
piezoelectric actuators or
magnetostrictive actuators are alternative options. They offer higher achievable 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 projector
A handheld projector (also known as a pocket projector, mobile projector, pico projector or mini beamer) is an image projector in a handheld device. It was developed as a computer display device for compact portable devices such as mobile p ...
s.
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 lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a #Compound lenses, compound lens consists of several simple lense ...
es 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
Laser color television (laser TV), or laser color video display, is a type of television that utilizes two or more individually modulated optical (laser) rays of different colors to produce a combined spot that is scanned and projected across the ...
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 array
In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving th ...
s. This method is used to scan
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
beams without moving parts. With the use of
Vertical-cavity surface-emitting laser
The vertical-cavity surface-emitting laser, or VCSEL , is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers (also ''in-plane'' lasers) which ...
(VCSELs), it might be possible to realize fast laser scanners in the foreseeable future.
Applications
3D object scanning
![High speed mobile laser scanning system](https://upload.wikimedia.org/wikipedia/commons/2/2a/High_speed_mobile_laser_scanning_system.jpg)
Within the field of
3D object scanning, laser scanning (also known as
lidar
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
) combines controlled steering of laser beams with a
laser rangefinder
A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...
. 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
Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...
.
''
3D object scanning'' allows enhancing the
design process
A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process or the result of that plan or specification in the form of a prototype, product, or process. The verb ''to design'' ...
, speeds up and reduces
data collection
Data collection or data gathering is the process of gathering and measuring information on targeted variables in an established system, which then enables one to answer relevant questions and evaluate outcomes. Data collection is a research com ...
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
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...
, scanning of buildings and building
interiors
''Interiors'' is a 1978 American drama film written and directed by Woody Allen. It stars Kristin Griffith, Mary Beth Hurt, Richard Jordan, Diane Keaton, E. G. Marshall, Geraldine Page, Maureen Stapleton, and Sam Waterston.
Allen's first ful ...
,
and in
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...
.
Material processing
Depending on the power of the laser, its influence on a working piece differs: lower power values are used for
laser engraving
Laser engraving is the practice of using lasers to engrave an object. Laser marking, on the other hand, is a broader category of methods to leave marks on an object, which in some cases, also includes color change due to chemical/molecular alte ...
and
laser ablation
Laser ablation or photoablation (also called laser blasting) is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser ...
, where material is partially removed by the laser. With higher powers the material becomes fluid and
laser welding
Laser beam welding (LBW) is a welding technique used to join pieces of metal or thermoplastics through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequen ...
can be realized, or if the power is high enough to remove the material completely, then
laser cutting
Laser cutting is a technology that uses a laser to vaporize materials, resulting in a cut edge. While typically used for industrial manufacturing applications, it is now used by schools, small businesses, architecture, and hobbyists. Laser cutt ...
can be performed. Modern lasers can cut steel blocks with a thickness of 10 cm and more or ablate a layer of the cornea that is only a few micrometers thick.
The ability of lasers to harden liquid polymers, together with laser scanners, is used in
rapid prototyping
Rapid prototyping is a group of techniques used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer aided design (CAD) data.
Construction of the part or assembly is usually done using 3D printin ...
, the ability to melt polymers and metals is, with laser scanners, to produce parts by
laser sintering or
laser melting
Selective laser melting (SLM) is one of many proprietary names for a metal additive manufacturing (AM) technology that uses a bed of powder with a source of heat to create metal parts. Also known as direct metal laser sintering (DMLS), the ASTM ...
.
The principle that is used for all these applications is the same:
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
that runs on a
PC or an
embedded system
An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...
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.
Barcode readers
Many
barcode reader
A barcode reader is an optical scanner that can read printed barcodes, decode the data contained in the barcode to a computer. Like a flatbed scanner, it consists of a light source, a lens and a light sensor for translating optical impulses into e ...
s, especially those with the ability to read bar codes at a distance of a few meters, use scanned laser beams. In these devices, a semiconductor laser beam is usually scanned with the help of a resonant mirror scanner. The mirror is driven electromagnetically and is made of a metal-coated polymer.
Space flight
When a space transporter has to dock to the space station, it must carefully maneuver to the correct position. In order to determine its relative position to the space station, laser scanners built into the front of the space transporter scan the shape of the space station and then determine, through a computer, the maneuvering commands. Resonant galvanometer scanners are used for this application.
Laser shows
Laser light show
A laser lighting display or laser light show involves the use of laser light to entertain an audience. A laser light show may consist only of projected laser beams set to music, or may accompany another form of entertainment, typically mus ...
s typically uses two galvanometer scanners on an X-Y configuration to draw patterns or images on walls, ceilings or other surfaces including theatrical smoke and fog for entertainment or promotional purposes.
References
{{DEFAULTSORT:Laser Scanning
Laser applications
Laser image acquisition
Lidar