What is the composition of the Suns atmosphere or rock on Mars?
What exhaust emissions does an internal combustion engine produce? Is it polystyrene or polypropylene on the conveyor belt in the refuse sorting plant? Spectrometers provide the answer. Solids, liquids and gases can be identified and analyzed with the spectral fingerprint. The key element in most spectrometers is a diffraction grating. Unlike prisms which diffract short-wave violet fractions of light more strongly than the long-wave red fractions, diffraction gratings provide an evenly fanned-out spectrum. Most diffraction grating spectrometers guide the spectrum produced directly onto a series of light-sensitive elements which measure the intensity of the signal for each color. From the light absorption of the material being analyzed, conclusions can be drawn about the chemical composition. Low-cost silicon diodes already exist for the visible light range. For measurements in the near-infrared or infrared spectrum, however, arrays are required which are made of several hundred gallium
