IR Polarizers

Download IR Polarizers Datasheet (PDF, 552 KB)

 
IR-polarizers operate in transmission and are designed to polarize IR radiation in the spectral region from 1.5 μm to MM waves. They are a sort of diffraction gratings and available on a variety of crystal and polymer substrates. The polarizer grating is made by forming grooves of a triangle profile on the substrate and subsequent deposition of a metal coating (aluminum) on one of the groove facets.

IR polaraizers

Applications

  • Microscop;
  • Thin film layer studies;
  • Semiconductors studies;
  • Electro-optic modulation systems;
  • Molecular orientation studies of crystal or polymer films;
  • Imaging;
  • Sensors and detectors;
  • Spectroscopic instruments.

Features

  • Used in wavelength range from NIR to MM;
  • Crystal and polymer substrates;
  • Very compact with short optical path;
  • High IR transmission;
  • High degree of polarization;
  • Polarizers are supplied in holders (protective ring with marked grid direction).

Tab. 1 Advantages of grid polarizers compared to other types of polarizers.

Grid polarizers Wire grid substrate-free polarizers Brewster and birefringent polarizers
Relatively low cost Valid Not valid
Compactness (optimal correlation between overall dimensions and clear aperture) Not valid Valid
Zero lateral image displacement at normal incidence Not valid Valid
Performance insensitive to the angle of incidence Not valid Valid
Possibility to use one polarizer for the wide wavelength range Valid Valid
High mechanical durability (for crystal polarizers) Valid Not valid

Types and specification:

Crystal

Polymer


Tab. 2 Parameters of IR-polarizers.

Substrate material CaF2 BaF2 ZnSe Ge Fluorine-
plast (teflon)
Hard poly-
ethylene
Spectral range, mm 1-9 1.5-12 1.5-14 8-14 1.5-7 2-7 >= 7
Typical operation aperture, mm 25 x 25 25 x 25 25 x 25 25 x 25 25 25
Standard holder size at typical aperture, mm D42 x 8 D42 x 8 D42 x 8 D42 x 8 D42 x 8 or
D34.9 x 7.9
D42 x 8 or
D34.9 x 7.9
Maximal operation aperture, mm 50 x 50/
/D50
50 x 50/
/D50
50 x 50/
/D50
50 x 50/
/D50
80 100 100
Grooves per mm 2400 1200 1200 1200 2400 1200 1200
Transmission efficiency K1 (average) >70% >70% 65-70% (back side AR coated) >50% (uncoated) >50% (back side AR coated) 75-85% 75-80% 70-80%
Transmission of unwanted radiation K2 1-2%@
1.5µm
<0.5%@
2 µm
<0,1@
3-9µm
1-2%@
2µm
<0.1%@
11µm
1-2%@
2µm
<0.1%@
10µm
<0.1%@
10µm
<1%@
1.5 µm
<0.5%@
2µm
<0.1%@
3-7µm
<2%@
1.5µm
<0.1%@
3µm
<1%@
8µm
<0.1%@
30-1000µm
Degree of polarization (K1-K2)/
(K1+K2)
94-97%
@1.5µm
>98%@
2µm
>99%@
3-9µm
94-97%
@2µm
>99%@
3-11µm
94-97%@
2µm
(AR coated)
92-96%@
2µm (uncoated)
>99%@
10µm
>99%@
10µm
>97%@
1.5µm
>99%@
2-7µm
>97%@
2µm
>99%@
3-7µm
>98%@
8µm
>99.5%@
30-1000µm
Extinction ratio
E=K1/(2*K2)
15-35@
1.5µm
70@
2µm
350@
3-9µm
15-35@
2µm
350@
11µm
15-35@
2µm
325-350@
10µm
(AR coated) 10-25@
2µm
250@
10µm (uncoated)
>250@ 10µm (uncoated) 40-45@
1.5µm
70-85@
2µm
380-430@
3-7µm
>40@
1.5µm
380-400@
3µm
35-40
@8µm
350-400@
30-1000µm

 

Sizes and shapes

Depending on the substrate material we produce polarizers using the ruled grating technique or the photolithography one.

Crystal polarizers

The grid is ruled onto the (normally) round substrate. After ruling the substrate is left uncut.

The shape of ruled area is shown below (polygon or round shape). These additional efforts are made to decrease the substrate size at the same clear aperture (for adjusting the polarizer into the standard setup).

 Non-standard grid shape

Polymer polarizers

The grid is ruled onto large size material, which is subsequently cut. Thus the clear aperture can be round.

The main standards for clear aperture (CA) of polarizers are D25mm and 25x25mm, which are available from our stock. Polarizers with non-standard sizes, shapes and operational wavelength regions are available on request.

Holder sizes at the standard aperture:
Crystal polarizers: D42mm x T8mm or D34.9mm x T7.9mm
Polymer polarizers: D42mm x T8mm or D34.9mm x T7.9mm


Anti-reflective (AR) coatings

Due to low refractive index of CaF2, BaF2, teflon, and polyethylene, there is no need for AR coatings for their effective operation.

However Germanium and Zinc Selenide have high refractive indices. Therefore to enhance the transmission of polarizers, we supply them Broad Band Antireflective coated over the whole transmission range.

Further enhancement of polarizer transmission is possible by optimizing the coating for specific wavelengths. The resulting transmission depends on the width of the coating spectral range (for narrower wavelength ranges, the transmission within this region is higher).

! Polarizers from our stock are not AR coated. Please request your polarizers depending on their operational spectral region, to optimize the parameters for ZnSe, or Ge items.

Spectral curves

Typical transmission and polarization curves are presented below.

For quotation and delivery please fill in our request form.