A fluorescence microscope is a microscope which is used to examine specimens with luminescent properties, or specimens which have been prepared with substances which create luminescent properties. In this type of microscopy, the specimen itself is the light source. A great deal of information can be collected with the use of a fluorescence microscope, and these microscopes can also be used to create stunning images in which detailed structures are clearly visible.
These microscopes take advantage of the properties of certain chemical compounds. When excited by light of the proper wavelength, classically ultraviolet light, these chemicals will light up. If the luminescence is brief, it is known as fluorescence, while a more prolonged period of luminescence after excitation is called phosphorescence. In both cases, the color of the luminescence will vary, depending on the chemicals involved, as will the precise length of the period of luminescence.
In a fluorescence microscope, light of a particular wavelength is passed through a specialized microscope condenser which focuses the light into a very narrow beam. When the light hits the specimen, the luminescent compounds become excited, and start to emit light. With the use of a dichroic mirror which filters out the beam of light used to excite the specimen, a researcher can clearly see the luminescence and make notes about its properties, or take a photograph of the specimen on the microscope stage for future reference.
Because the light used in a fluorescence microscope is often potentially dangerous to the eyes, it is usually necessary to use a polarizing filter on the eye piece so that the user's eyes are not damaged by the microscope. Polarizing filters can also be used for color correction, or to increase contrast, so that the luminescence is more clearly visible. As with other microscopes, the clarity of the image can be adjusted by focusing the components of the microscope, and the level of magnification can also be raised or lowered as needed.
In some cases, a specimen may be naturally luminescent, as in the case of some minerals which will fluoresce or phosphoresce under light of a particular wavelength. Specimens can also be tagged with molecules known as fluorophores. These molecules can target specific structures within the specimen, creating a fluorescent image of structures of note when the specimen is excited by the light in the microscope.
A fluorescence microscope can be an expensive purchase, especially in the case of high-quality microscopes. As a general rule, this type of microscopy is only available to very well equipped laboratories.