Prism spectrometer

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Experimental setup of a prism spectrometer
Long-wave radiation on the prism spectrometer
Short-wave radiation on the prism spectrometer

A prism spectrometer is an optical spectrometer which uses a prism as a dispersive element . In contrast to a prism monochromator , you can record a complete spectrum at the same time.


Structure of a prism spectrometer

A prism spectrometer breaks down the incident light into its individual colors or wavelengths . Since a prism has only one angular dispersion (due to the double refraction in the same direction at interfaces, the different wavelengths are deflected by different angles), the deflection angle must be determined with a rotatable lens . If the refractive index of the prism is known, the wavelength can be determined from it. The decisive criterion is that the refractive index depends on the wavelength and that the prism has a non-linear course.

If you replace the prism with a diffraction grating , you get a grating spectrometer . Grids are not only cheaper, but also easier to calibrate due to the linear diffraction dependence on the wavelength. However, gratings always have greater losses than prisms, but are preferred due to their significantly higher resolution.



The spectrum of a fluorescent lamp

Prism spectrometers can be used to draw conclusions about the composition of a medium that emits the light via the determined spectral lines . Suitable emitting media are, for. B. metal vapor lamps (e.g. mercury vapor lamps ), as they do not emit a continuous spectrum in contrast to incandescent solids (not all visible wavelengths are included in the spectrum). In metal vapor lamps, the electrons in the metal atoms are raised to higher energy levels and emit certain wavelengths when they return to their original state. These wavelengths depend on the level to which the electrons are raised and how far they "fall" again. Because different metal atoms also have different energy levels , each metal halide lamp has its own characteristic emission spectrum , which can be analyzed with the help of the prism spectrometer.

Measurement of the refractive index

A prism spectrometer can be used to measure the refractive index of a material if the wavelengths of the radiation used are known. The calibration of a prism spectrometer is therefore carried out with known spectral lines from vapor lamps or laser light sources.