Windows are used to allow optical radiation to pass from one environment to another without allowing other components of these environments to mix. The environments may vary widely in temperature, pressure, chemical composition, phase or cleanliness. The criteria used to select the appropriate windows may include wavelength transmission, scattering, wavefront distort and resistance to certain environments.

PHOTOP windows are available in a wide range of sizes and materials including BK7, Barium Fluoride, Fused Silica and Sapphire.