Polarisers are used to produce polarized light. Thin-film polarisers are used in high-power applications, whereas polarization cubes are used for simultaneous beam separation. Gratings can also be used for polarization.
For the mid infrared
Ruled wire grid polarisers are produced on calcium fluoride (CaF2) and zinc selenide substrates (ZnSe) and holographic wire grid polarisers on ZnSe, CaF2, BaF2 and KRS-5. They cover a wavelength range from 2 µm to 20 µm.
The surface of a wire grid polariser, like any diffraction grating, is extremely delicate. Nothing should ever be allowed to touch the surface of the polariser. Handling, when necessary, should be by the edge only and with protected fingers. Careful removal of dust by gentle air flow is the only cleaning procedure recommended. Particular care should be used when handling KRS-5.
AR coating is available on ZnSe
An interferometrically generated interference pattern is produced from monochromatic light and exposed onto a substrate. Once developed, the resist has a regular sinusoidal profile that is vacuum aluminized at an oblique angle to create the array of parallel conductors.
The fabrication of holographic wire grid polarisers permits the use of a wide variety of infrared materials that do not lend themselves to the ruling process. They are available with a spacing of 2700 grooves/mm for optimum short-wavelength efficiency.
Calcium fluoride and barium fluoride have low refractive index (high Tx) values and do not require anti-reflective (AR) coatings.
Zinc selenide has a high refractive index and transmission at specific wavelength regions, which can be enhanced by an
AR coating on the rear surface only. Zinc selenide is usually optimized for transmission at specific laser lines, typically from 9 to 11 µm.
KRS-5 is not normally AR coated because this would limit its broad transmission range, which is its primary advantage.
Ruled wire grid polarisers are available in five standard sizes (15-mm square, 15-, 25-, 38-, and 50-mm diameter).
Holographic wire grid polarisers are currently available in a standard 25-mm diameter size, unmounted or mounted in a double protective ring.