# Excitation filter

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{{Short description|Optical filter in fluorescence microscopy}}
An '''excitation filter''' is a high quality optical-glass filter commonly used in [fluorescence microscopy](/source/Fluorescence_microscope) and [spectroscopic](/source/Spectroscopy) applications for selection of the excitation wavelength of light from a light source. Most excitation filters select light of relatively short wavelengths from an excitation light source, as only those wavelengths would carry enough energy to cause the object the microscope is examining to fluoresce sufficiently.<ref>Light with shorter wavelengths have higher energy, according to the [Planck relation](/source/Planck_relation) <math>E = hc/ \lambda</math></ref> The excitation filters used may come in two main types — ''short pass filters'' and ''[band pass filter](/source/band_pass_filter)s''.<ref name="Reichman">{{cite web | last = Reichman| first = Jay| title = Handbook of Optical Filters for Fluorescence Microscopy| publisher = Chroma Technology Corp.| date = June 1998| url = http://depts.washington.edu/keck/handbook3.pdf| access-date = 25 March 2015 }}</ref> Variations of these filters exist in the form of ''[notch filter](/source/notch_filter)s'' or deep blocking filters (commonly employed as [emission filters](/source/emission_filters)). Other forms of excitation filters include the use of [monochromator](/source/monochromator)s, [wedge prism](/source/wedge_prism)s coupled with a narrow slit (for selection of the excitation light) and the use of [holographic](/source/holographic) [diffraction grating](/source/diffraction_grating)s, etc. [for [beam diffraction](/source/beam_diffraction) of white laser light into the required excitation wavelength (selected for by a narrow slit)].

An excitation filter is commonly packaged with an emission filter and a [dichroic](/source/dichroic) [beam splitter](/source/beam_splitter) in a cube so that the group is inserted together into the microscope. The dichroic beam splitter controls which wavelengths of light go to their respective filter.<ref name="Reichman"/><ref>{{cite book | last = Lakowicz| first = Joseph R.| title = Principles of Fluorescence Spectroscopy| publisher = Springer Science+Business Media| edition = 3rd| date = 5 December 2007| location = New York| pages = 41| url = https://books.google.com/books?id=-PSybuLNxcAC&pg=PA41| isbn = 9780387463124}}</ref>

==References==
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Category:Optical filters

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Adapted from the Wikipedia article [Excitation filter](https://en.wikipedia.org/wiki/Excitation_filter) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Excitation_filter?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.