ABSTRACT
A filter device modifies the distribution of the content of spatial frequencies in the wavefront (spatial filter) or the content of the temporal frequencies or wavelengths in the light beam (spectral filters). Basically, with spatial filters we can modify the spatial coherence and with a temporal filter we can modify the temporal coherence or chromaticity of a light beam. These two types of filters and their applications are fully described in this chapter, including the 4f spatial filters, the thin-interference films, and the acousto-optic filters.
