BROAD BAND POLARIZING CUBES

For a beam of light incident on a surface at normal incidence, polarization properties of the reflected and transmitted beams are described by Fresnel's equations. According to these, if angle of incidence is equal to Brewster's angle, the degree of polarization of reflected -s beam ( perpendicular to plane of incidence ) is unity. The transmitted -p ( parallel to plane of incidence ) beam is partially polarized. Polarization of the transmitted beam can be further purified by successive films each of suitable thickness and refractive index so that Brewster's condition at each interface is met. In actual practice this does not happen which limits the performance of thin film polarizing cubes.

The standard available cube sizes are 5, 12, 25 and 50 mm. Standard central wavelengths are 550, 830, 1100 and 1400 nm. These are all made of SF2 substrate. Other sizes and wavelengths are available on special order. All outside faces of the cubes are broad band single layer magnesium fluoride anti-reflection coated ( 1.5 % average reflectivity per surface in respective wavelength ranges as shown in following plots ). Please visit our Anti-Reflection Coating page on this web site for various reflectivity plots.

The extinction of transmitted -p component is at least 1 part in 500. As shown in the following plots, some of the transmitted -p polarization is reflected which degrades the extinction of -s polarization. Almost all -s polarization is reflected. Wavefront deformation of the transmitted -p beam is at least quarter wave at 633 nm.