Atomic Line Filter - Common Components

Common Components

Preceding an atomic line filter may be a collimator, which straightens incident light rays for passing through the rest of the filter consistently; however, collimated light is not always necessary. After the collimator, a high-pass filter blocks almost half of the incoming light (that of too long a wavelength). In Faraday and Voigt filters, the first polarizing plate is used here to block light.

The next component in an atomic line filter is the vapor cell; this is common to all atomic line filters. It either absorbs and re-emits the incident light, or rotates its polarization by the Faraday or Voigt effect. Following the vapor cell is a low-pass filter, designed to block all of the light that the first filter did not, except the designated frequency of light which came from the fluorescence. In Faraday and Voigt filters, a second polarizing plate is used here.

Other systems may be used in conjunction with the rest of an atomic line filter for practicality. For instance, the polarizers used in the actual Faraday filter don’t block most radiation, "because these polarizers only work over a limited wavelength region … a broad band interference filter is used in conjunction with the Faraday filter". The passband of the interference filter may be 200 times that of the actual filter. Photomultiplier tubes, too, are often used for increasing the intensity of the output signal to a usable level. Avalanche photomultipliers, which are more efficient, may be used instead of a PMT.