Fresnel Rhomb Retarders

Fresnel prism rhomb is advantageous than reflective phase retarder and waveplate that use birefringence material. The retardation depends on the index of refraction of material and geometry but not the design wavelength. The desired phase shift can be constructed by shining light in the 8-12µm region at a selected incident angle, allowing it to make the required number of internal reflections by using the principle of total internal reflection. The rhomb improves the quality of laser cutting in laser processing applications.

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Part Number	Wavelength (µm)	Dimensions (mm)	Angle	Retardation
WFP4-51.5x13.2x12Z	8.0 - 12.0	51.5 x 13.2 x 12.0	65°, 115°	λ/4
WFP4-58.3x15x13.6Z	8.0 - 12.0	58.3 x 15.0 x 13.6	65°, 115°	λ/4
WFP2-26.5x15x39.1Z	8.0 - 12.0	26.5 x 15.0 x 39.1	123°, 147°	λ/2

Material: Zinc Selenide (ZnSe)
Dimensional Tolerance: +/- 0.1mm
Type: Quarter Wave & Half-Wave
Angular Deviation: 0.2°
Surface Quality: 60/40
Coating: Options Available
Polishing: required@ Input, output, top and bottom surfaces

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

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

Fresnel Rhomb Quarter Wave Retarder: Single Component with Single Reflection

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

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

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