What is a monochromator?
A monochromator isolates a certain wavelength from incoming broadband electromagnetic radiation (e.g. light, x-ray radiation). The incoming electromagnetic radiation is sent through an entrance slit, collimated by optics and directed onto a prism or diffraction grating. This separates the electromagnetic radiation according to wavelength. A second collimator then maps the light from one direction and therefore only in one wavelength onto the exit slit. The isolated wavelength emerges at the exit slit. The desired wavelength can be set by turning the prism or grating.
On the one hand, monochromators can be used to analyze light by measuring the power of the light of a certain wavelength (with a given bandwidth) behind the exit slit. On the other hand, with a monochromator and a broadband light source, monochromatic light can be generated over a wide spectral range (tunable light source).
Among the uses of monochromators are in fluorescence spectroscopy, reflection spectroscopy and transmission spectroscopy, for testing sensors and solar cells, in polarimetry, as well as in refractometry.
The most important specifications of a monochromator are the bandwidth of the monochromatic light at the exit slit, wavelength range over which it can be used, and the efficiency with which it can isolate a wavelength.
Figure 1: Grating monochromator with mirrors as collimators