= Total internal reflection fluorescence microscopy
<Total internal reflection fluorescence microscopy> excites labels close to a boundary using the <evanescent wave> accompanying <total internal reflection>. Illumination travels through the higher-<refractive index> side, typically a coverslip, at an angle above the <critical angle for total internal reflection>. The field penetrates the specimen side but decays with distance from the interface.
A prism or a sufficiently high-<numerical aperture> <microscope objective> supplies the required incidence. This confines excitation near the surface and reduces background from deeper fluorescent material, making it useful for surface-associated molecular events. Changing incidence angle changes the depth weighting; an <intensity> change can therefore reflect vertical motion as well as molecule number.<Total Internal Reflection Fluorescence Microscopy by University of California San Francisco>[Technique description: evanescent excitation close to the interface]{ref}
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