Editing Spatial light modulator (section)

{{Short description|Optical device}}
{{More footnotes needed|date=March 2010}}
[[File:Liquid Crystal based Spatial Light Modulator.gif|thumb|Schematic of a liquid crystal-based Spatial Light Modulator. Liquid crystals are birefringent, so applying a voltage to the cell changes the effective refractive index seen by the incident wave, and thus the phase retardation of the reflected wave.]]
A '''spatial light modulator''' ('''SLM''') is a device that can control the [[Intensity (physics)|intensity]], [[Phase (waves)|phase]], or [[Polarization (waves)|polarization]] of [[light]] in a spatially varying manner. A simple example is an [[overhead projector]] [[Transparency (projection)|transparency]]. Usually when the term SLM is used, it means that the transparency can be controlled by a [[computer]].

SLMs are primarily marketed for [[Projector|image projection]], displays devices,<ref>{{Cite journal |last=Jullien |first=Aurélie |date=2020-03-01 |title=Spatial light modulators |url=https://web.archive.org/web/20221031003350if_/https://www.photoniques.com/fr/articles/photon/pdf/2020/02/photon2020101p59.pdf |journal=Photoniques |volume=101 |language=en |issue=101 |pages=59–64 |doi=10.1051/photon/202010159 |bibcode=2020Phot..101...59J |issn=1629-4475}}</ref> and [[maskless lithography]].{{Citation needed|date=June 2022}} SLMs are also used in [[Optical computer|optical computing]] and [[Optical tweezers|holographic optical tweezers]].

Usually, an SLM modulates the intensity of the light beam. However, it is also possible to produce devices that modulate the phase of the beam or both the intensity and the phase simultaneously. It is also possible to produce devices that modulate the polarization of the beam, and modulate the polarization, phase, and intensity simultaneously.<ref>{{Cite journal |last1=Moreno |first1=Ignacio |last2=Davis |first2=Jeffrey A. |last3=Hernandez |first3=Travis M |last4=Cottrell |first4=Don M. |last5=Sand |first5=David |date=2011-12-21 |title=Complete polarization control of light from a liquid crystal spatial light modulator |url=http://dx.doi.org/10.1364/oe.20.000364 |journal=Optics Express |volume=20 |issue=1 |pages=364–376 |doi=10.1364/oe.20.000364 |pmid=22274360 |issn=1094-4087}}</ref>

SLMs are used extensively in [[holographic data storage]] setups to encode information into a laser beam similarly to the way a transparency does for an overhead projector. They can also be used as part of a [[phased array optics|holographic display technology]].

In the 1980s, large SLMs were placed on overhead projectors to project computer monitor contents to the screen. Since then, more modern [[Video projector|projectors]] have been developed where the SLM is built inside the projector. These are commonly used in meetings for presentations.

Liquid crystal SLMs can help solve problems related to laser microparticle manipulation. In this case spiral beam parameters can be changed dynamically.<ref>{{cite journal|url=http://ntv.ifmo.ru/en/article/13846/primenenie_prostranstvennyh_modulyatorov_svetadlya_formirovaniya_lazernyh_puchkov_so_spiralnymraspredeleniem_fazy.htm|title=Application of spatial light modulators for generation of laser beams with a spiral phase distribution.|author=Zinchik A.A.|journal=Scientific and Technical Journal of Information Technologies, Mechanics and Optics|volume=15|issue=5|pages=817–824|year=2015|doi=10.17586/2226-1494-2015-15-5-817-824|doi-access=free}}</ref>