Fabry-Perot Interference Filters.

The discrimination of coherent, laser radiation from incoherent, white-light radiation can be accomplished with properly designed interference filters that make use of the coherent nature of laser radiation in addition to its narrow-band spectral character. In this study it is assumed that we wish to block high power laser radiation from a detector without impeding its ability to see light emitted by broad-band, incoherent, weak continuum sources. We analyze two types of Fabry-Perot, air spaced filters 1 the tunable two- or multiplate Fabry-Perot interferometer and 2 a multiplate stack of 14-wave plates. It is shown that the Fabry-Perot interferometer has a limited rejection ratio for coherent radiation, but offers the possibility of relatively large tuning range. By contrast, the rejection ratio for coherent radiation of quarter-wave plates can be made as large as 10000 with a white-light transmission of 20, and a bandwidth delta lambdalambda sub O 0.03. However, the tuning range of such a stack will be limited. Author