Lasers are sources of light with very special properties, as discussed in the article on laser light. For that reasons, there is a great variety of laser applications. The following sections give an overview.
Manufacturing
Lasers are widely used in manufacturing, e.g. for cutting, welding, soldering, surface treatment, marking, micromachining, pulsed laser deposition, lithography, alignment, etc. In most cases, relatively high optical intensities are applied to a small spot, leading to intense heating, possibly evaporation and plasma generation. Essential aspects are the high spatial coherence of laser light, allowing for strong focusing, and often also the potential for generating intense pulses.
Laser processing methods have many advantages, when being compared to mechanical approaches. They allow to fabricate very fine structures with high quality, avoiding mechanical stress as caused e.g. by mechanical drills and blades. A laser beam with high beam quality can be used to drill very fine and deep holes, e.g. for injection nozzles. A high processing speed is often (but not always) achieved, and it can also be advantageous to process materials without touching them.
Medical Applications
There is a wide range of medical applications. Often these relate to the outer parts of the human body, which are easily reached with light; examples are eye surgery and vision correction (LASIK), dentistry, dermatology (e.g. photodynamic therapy of cancer), and various kinds of cosmetic treatment such as tattoo removal or hair removal.
Lasers are also used for surgery (e.g. of the prostate), exploiting the possibility to cut tissues while causing only a low amount of bleeding.
Very different types of lasers are required for medical applications, depending on the optical wavelength, output power, pulse format, etc. In many cases, the laser wavelength is chosen so that certain substances (e.g. pigments in tattoos or caries in teeth) absorb light more strongly than surrounding tissue, so that they can be more precisely targeted.
Medical lasers are not always used for therapy. Some of them rather assist the diagnosis e.g. via methods of laser microscopy or spectroscopy (see below).
Metrology
Lasers are widely used in optical metrology, e.g. for extremely precise position measurements with interferometers, for long-distance range finding and navigation.
Laser scanners are based on collimated laser beams, which can read e.g. bar codes or other graphics over some distance. It is also possible to scan three-dimensional objects, e.g. in the context of crime scene investigation (CSI).
Optical sampling is a technique applied for the characterization of fast electronic microcircuits, microwave photonics, terahertz science, etc.
Lasers also allow for extremely precise time measurements and are therefore essential ingredient of optical clocks which will soon outperform the currently used atomic cesium clocks.
Fiber-optic sensors, often probed with laser light, allow for the distributed measurement of temperature, stress, and other quantities e.g. in oil pipelines and wings of airplanes.
Data Storage
Optical data storage e.g. in compact disks (CDs), DVDs, HD-DVDs, blu-ray disks and magneto-optical disks, is nearly always relying on a laser source, which has a high spatial coherence and can thus be used to address very tiny spots in the recording medium, allowing a very high density data storage. Another case is holography, where the temporal coherence can also be important.
Communications
Optical fiber communications, extensively used particularly for long-distance optical data transmission, mostly relies on laser light in optical glass fibers. Free-space optical communications e.g. for inter-satellite communications is based on higher power lasers, generating collimated laser beams which propagate over large distances with small beam divergence.
Displays
Laser projection displays containing RGB sources can be used for cinemas, home videos, flight simulators, etc., and are often superior to other displays concerning possible screen dimensions, resolution and color saturation. Further reductions of manufacturing costs will be essential for deep market penetration.
Spectroscopy
Laser spectroscopy is useful e.g. in atmospheric physics and pollution monitoring (e.g. trace gas sensing with differential absorption LIDAR technology). It also plays a role in medicine (e.g. cancer detection), biology, and various types of fundamental research, partly related to metrology (see above).
Microscopy
Laser microscopes and setups for coherence tomography provide images e.g. of biological samples with very high resolution, often in three dimensions. It is also possible to realize functional imaging.
Various Scientific Applications
Laser cooling makes it possible to bring clouds of atoms or ions to extremely low temperatures. This has applications in fundamental research as well as for industrial purposes.
Laser guide stars are used in astronomical observatories in combination with adaptive optics for atmospheric correction. They allow a substantially increased image resolution even in cases where a sufficiently close-by natural guide star is not available.
Military Applications
There are various military laser applications. In relatively few cases, lasers are used as weapons; the "laser sword" has become quite popular via films, but not in practice. Some high power lasers are currently developed for potential use on the battle field, or for destroying missiles, projectiles and mines.
In other cases, lasers function as target designators or laser sights (essentially laser pointers emitting visible or invisible laser beams), or as irritating or blinding (normally not directly destroying) countermeasures e.g. against heat-seeking anti-aircraft missiles. It is also possible to temporarily or permanently blind soldiers with laser beams, although the latter is forbidden by rules of war.
There are also many laser applications which are not specific for military use, e.g. in areas like range finding, LIDAR, and optical communications.
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