Editing Fluorescence microscope (section)

==Principle==
The specimen is illuminated with light of a specific [[wavelength]] (or wavelengths) which is absorbed by the [[fluorophore]]s, causing them to emit light of longer wavelengths (i.e., of a different color than the absorbed light). The illumination light is separated from the much weaker emitted fluorescence through the use of a spectral emission filter. Typical components of a fluorescence microscope are a light source ([[xenon arc lamp]] or [[mercury-vapor lamp]] are common; more advanced forms are high-power [[LED]]s and [[laser]]s), the [[excitation filter]], the [[dichroic mirror]] (or [[dichroic filter|dichroic beamsplitter]]), and the [[emission filter]] (see figure below). The filters and the dichroic beamsplitter are chosen to match the spectral excitation and emission characteristics of the fluorophore used to label the specimen.<ref name="Spring-2024"/> In this manner, the distribution of a single fluorophore (color) is imaged at a time. Multi-color images of several types of fluorophores must be composed by combining several single-color images.<ref name="Spring-2024"/>

Most fluorescence microscopes in use are epifluorescence microscopes, where excitation of the fluorophore and detection of the fluorescence are done through the same light path (i.e. through the objective). These microscopes are widely used in biology and are the basis for more advanced microscope designs, such as the [[confocal microscopy|confocal microscope]] and the [[total internal reflection fluorescence microscope]] (TIRF).

===Epifluorescence microscopy===
[[File:FluorescenceFilters 2008-09-28.svg|thumb|right|Schematic of a fluorescence microscope]]
The majority of fluorescence microscopes, especially those used in the [[life sciences]], are of the epifluorescence design shown in the diagram. Light of the excitation wavelength illuminates the specimen through the [[objective (optics)|objective]] lens. The [[fluorescence]] emitted by the specimen is focused to the detector by the same objective that is used for the excitation which for greater resolution will need objective lens with higher [[numerical aperture]]. Since most of the excitation light is transmitted through the specimen, only reflected excitatory light reaches the objective together with the emitted light and the epifluorescence method therefore gives a high signal-to-noise ratio. The dichroic beamsplitter acts as a wavelength specific filter, transmitting fluoresced light through to the eyepiece or detector, but reflecting any remaining excitation light back towards the source.{{cn|date=February 2024}}