LWIR Fresnel Rhomb Retarder Application Note

Author: Yingli – R&D Director

Fresnel rhomb wave retarders are made of common glass. The Retardation of Fresnel Rhomb retarders only depends on the refractive index and geometry of the optics. Thus, they can be used in a much broader wavelength range than achromatic waveplates which are made from birefringent crystal, especially in the LWIR range where the dispersion of the material over that range is not significant.

For quarter wave Fresnel Rhomb retarders, there are three types in our product line:

  • A single-component Fresnel Rhomb Quarter Wave Retarder with a double reflection.
    • It produces a phase retardation of λ/4.
    • The output light is parallel to the input light but is laterally displaced.
  • A single component Fresnel Rhomb Quarter Wave Retarder with a single reflection.
    • It also produces a phase retardation of λ/4.
    • But the output and input light has an angle of 66 degrees between them.
  • A double component Fresnel Rhomb Quarter Wave Retarder.
    • It consists of two wave retarders, each producing a phase retardation of λ/8.
    • The pair then has total retardation of λ/4, the same as in a single Fresnel Rhomb quarter wave retarder.
    • The input and output are parallel and are in the same lines as well without lateral displacement.

For a half-wave Fresnel Rhomb retarder, there is only one type. It is a single component and has a double reflection. The output light is parallel to the input light but is laterally displaced.

Fresnel Rhomb Quarter Wave Retarder: Single Component with Double Reflection

LWIR Fresnel Rhomb Retarder 1
Figure 1.

Material: ZnSe
Cross section: 10×10 mm2 or 30 x 30 mm2 (or as requested)
Working wavelength Range: 7-13 um
Surface Quality: 60/40 scratch and dig

LWIR Fresnel Rhomb Retarder 3
Figure 2.

Fresnel Rhomb Quarter Wave Retarder: Single Component with Single Reflection

LWIR Fresnel Rhomb Retarder 5
Figure 3.

Material: ZnSe
Cross section: 15×15 mm2 or 30 x 30 mm2 (or as requested)
Working wavelength Range: 7-13 um
Surface Quality: 60/40 scratch and dig

LWIR Fresnel Rhomb Retarder 7
Figure 4.

Fresnel Rhomb Octant Wave Retarder: Co-axis Double Components, Fourth Reflection

Material: ZnSe
Cross section: 10×10 mm2 or 30 x 30 mm2 (or as requested)
Working wavelength Range: 7-13 um

LWIR Fresnel Rhomb Retarder 9
Figure 5.
LWIR Fresnel Rhomb Retarder 11
Figure 6

Half Wave Fresnel Rhomb Retarder: Single Component, Double Reflection

Material: ZnSe
Cross section: 10×10 mm2 or 30 x 30 mm2 (or as requested)
Working wavelength Range: 7-13 um
Surface Quality: 60/40 scratch and dig

LWIR Fresnel Rhomb Retarder 13
Figure 7.

Phase Retarder Dispersion in MWIR and LWIR

Phase retardation vs wavelength for quarter wave
Fresnel Rhomb Retarder

Phase retardation vs wavelength for quarter wave
Fresnel Rhomb Retarder

LWIR Fresnel Rhomb Retarder 15
Figure 8.

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