Superachromatic Quartz and MgF2 Retarders

The retarders are produced with a path difference of λ/2 or λ/4. Each retarder consists of three pairs of quartz and MgF₂ plates cemented to each other. The deviation is up to about 2'.
The standard version has a calculated path difference (R) of λ/2 ± 1.3% or λ/4 ± 4% in the spectral range of 310 to 1100 nm. In the entire wavelength range the orientation of the fast axis (Ψ) changes ± 2° with the λ/2 plate or ± 1.5°with the λ/4 plate. The 6 crystal plates are cemented with cover plates made from fused silica Suprasil. The outer surfaces are single-layer antireflection coated.
The retarders in the spectral range of 600 - 2700 nm have a calculated path difference of λ/2 ± 0.04% or λ/4 ± 0.25%. The orientation of the optical axis changes ±  0.2° with the λ/2 plate and ±  0.1° with the λ/4 plate. The retarders for this range are delivered without cover plates. The outer surfaces are single-layer antireflection coated.
During manufacturing it is possible to achieve the theoretical retardation (see curves) to an accuracy of about 3%.
This type of retardation plates can be specially ordered for other wavelengths.

The retarders are supplied in a cylindrical mount engraved with the average direction of the axis, the path difference and the wavelength range.

Diagrams

Literature

• K. Serkowsky, Methods of Experimental PhysicsVol 12: Astrophysics, Part A, N. P. Carleton, Hrsg, (1974), S.361
• J. E. Frecker, K. Serkowsky, Applied Optics 15,(1976), S.605 "Linear Polarimeter with Rapid Modulation, Achromatic in the 0,3 - 1,1 µm range"