{{Short description|Optical element that reflects and diffracts light}} thumb|upright=1.5|Simplified working principle of grisms
A '''grism''' (also called a '''grating prism''') is a combination of a prism and grating arranged so that light at a chosen central wavelength passes straight through.<ref>Palmer, C., & Loewen, E. G. (2005). [https://www.uobabylon.edu.iq/eprints/publication_11_13268_167.pdf Diffraction Grating Handbook] Newport Corporation 2005, p.265 Retrieved 2025-07-14 </ref> The advantage of this arrangement is that one and the same camera can be used for both imaging (without the grism) and spectroscopy (with the grism) without having to be moved. Grisms are inserted into a camera beam that is already collimated. They then create a dispersed spectrum centered on the object's location in the camera's field of view.<ref>{{Cite web |title=Grism developments for space- and ground-based astronomy |url=https://spie.org/news/3739-grism-developments-for-space--and-ground-based-astronomy |access-date=2025-07-14 |website=spie.org}}</ref>
The resolution of a grism is proportional to the tangent of the wedge angle of the prism in much the same way as the resolutions of gratings are proportional to the angle between the input and the normal to the grating. The dispersed wavefront sensing system (as part of the NIRCam instrument) on the James Webb Space Telescope uses grisms. The system allows coarse optical path length matching between the different mirror segments.<ref name="Camera">{{Cite book |last=Greene|first=Thomas P. |editor-first1=Howard A |editor-first2=Giovanni G |editor-first3=Makenzie |editor-first4=Natalie |editor-first5=Nicholas |editor-first6=Edward C |editor-last1=MacEwen |editor-last2=Fazio |editor-last3=Lystrup |editor-last4=Batalha |editor-last5=Siegler |editor-last6=Tong |display-authors=etal|year=2016|chapter=Slitless spectroscopy with the James Webb Space Telescope Near-Infrared Camera (JWST NIRCam) |title=Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave |series=Proceedings of the SPIE |volume=9904 |pages=99040E |arxiv=1606.04161|bibcode=2016SPIE.9904E..0EG|doi=10.1117/12.2231347 |isbn=978-1-5106-0187-1|s2cid=119271990 }}Retrieved 2025-07-14</ref>
== History == The grating prism was first described in 1973 by Ira Sprague Bowen and Arthur H. Vaughan Jr. in a paper explaining an experiment using a "non-objective grating" located in the convergent beam of a telescope, which allowed to significantly reduce its off-axis aberrations.<ref>Ira Bowen et Arthur H. Vaughan, Jr. ''Publications of the Astronomical Society of the Pacific'', The University of Chicago Press, 1973, <abbr>p.</abbr> 174-176 <small>(DOI 10.1086/129428, JSTOR 40675355)</small> Retrieved 2025-07-14</ref> In 1997, this instrument was patented by Chungte W. Chen and Ernest W. Gossett (No 5,652,681), the name grism is a portmanteau of grating-prism.<ref>{{Cite patent|number=US5652681A|title=Grism (grating-prism combination)|gdate=1997-07-29|invent1=Chen|invent2=Gossett|inventor1-first=Chungte W.|inventor2-first=Ernest W.|url=https://patents.google.com/patent/US5652681/en}} Retrieved 2025-07-14</ref>
==See also== * Diffraction grating * Echelle grating * Slitless spectroscopy
==References== {{reflist}} ===Further reading=== *{{Cite book |last=Kitchin |first=C. R. |url=https://www.taylorfrancis.com/books/9780429956997 |title=Astrophysical Techniques |date=July 27, 2020 |publisher=CRC Press |isbn=978-0-429-49113-9 |edition=7 |location=Seventh edition. {{!}} Boca Raton : CRC Press, 2020. |language=en |doi=10.1201/9780429491139}} *The Near Infrared Camera and Multi-Object Spectrometer includes a grism http://www.stsci.edu/hst/nicmos/design/grisms * {{Cite journal |last=Deen |first=Casey P. |last2=Gully-Santiago |first2=Michael |last3=Wang |first3=Weisong |last4=Pozderac |first4=Jasmina |last5=Mar |first5=Douglas J. |last6=Jaffe |first6=Daniel T. |date=May 8, 2017 |title=A Grism Design Review and the As-Built Performance of the Silicon Grisms for ''JWST''-NIRCam |journal=Publications of the Astronomical Society of the Pacific |volume=129 |issue=976 |article-number=065004 |doi=10.1088/1538-3873/129/976/065004 |issn=0004-6280|arxiv=1611.09923 }} A review of grism design for astronomy.
Category:Prisms (optics) Category:Diffraction Category:Diffraction gratings Category:Optical components