Polarizers are used to produce polarized light. Thin-film polarizers are used in high-power applications, whereas polarization cubes are used for simultaneous beam separation. Gratings can also be used for polarization.
Wire Grid Polarizers
For the mid infrared
Ruled wire grid polarizers are produced on calcium fluoride (CaF2) and zinc selenide substrates (ZnSe) and holographic wire grid polarizers on ZnSe, CaF2, BaF2 and KRS-5. They cover a wavelength range from 2 µm to 20 µm.
The surface of a wire grid polarizer, like any diffraction grating, is extremely delicate. Nothing should ever be allowed to touch the surface of the polarizer. 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.
- Wire grid spacing: 1200 g/mm
- Parallelism: ≤ 3 arc min.
- Surface flatness: l/20 @ 10.6 µ
- Groove parallelism to edge: ± 0.5°
- Diameter tolerance: ± 0.5 mm
- Substrate thickness: 2.5 mm ± 1 mm
- Ring thickness tolerance: ± 0.1 mm
- Damage threshold: CW laser: 100 W/cm²
- Pulsed laser (100 nsec. pulse): 2 J/cm²
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 polarizers 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.
- 2700 groove/mm
- Substrates: Calcium Fluoride (CaF2), Barium Fluoride (BaF2), Zinc Selenide (ZnSe) and KRS-5
- For improved short wavelength performance
- Extended infrared range
- High transmission
- High extinction ratios
- 360° bench mountable, rotary stage for FTIR spectrometers
- All polarizers can be mounted in a double protective ring
- Wire grid spacing: 2700 grooves/mm (nom)
- Parallelism: ≤ 3 arc min.
- Substrate thickness: 2 mm nominal
- Ring thickness: ± 0.1 mm
- Dimensional tolerance: ± 0.5 mm
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 polarizers are available in five standard sizes (15-mm square, 15-, 25-, 38-, and 50-mm diameter).
Holographic wire grid polarizers are currently available in a standard 25-mm diameter size, unmounted or mounted in a double protective ring.