General Technical Information about Waveplates / Retardation Plates

Most retardation plates are either quarter wave (λ/4) plates or half wave (λ/2) plates. Quarter wave plates create a phase shift of one quarter of the wavelength (λ/4, π/2, 90°) and can convert linear polarization to circular polarization and vice versa. They are often used with a linear polarizer to form an isolator, blocking light reflected back from other surfaces (ellipsometry, optical pumping, isolation).

Half wave plates retard one polarization direction by one half of the wavelength (λ/2, π, 180°), effectively changing the direction of linear polarization, depending on the orientation of incident linear polarization with respect to the crystal axis. Therefore they can be used as continuously adjustable polarization rotators e.g. in electro optical modulation or as a variable beam splitter when used in combination with a polarizing beam splitter.

Retardation plates can be made from various birefringent materials such as quartz, mica and even special polymers. Different materials lend themselves to different types of retardation plates. Quartz, for example, is not suitable for the production of true zero order plates, but has some other desirable properties. Mica, on the other hand, is perfect for true zero order plates, but has strong absorption in the UV. You find a clear discussion of the pros and cons of the different types and materials in our Waveplates Selection Guide.

We are the leader in mica retardation plates. However, we do not specialize in mica because it is a “simple” material; on the contrary, mica is an extremely difficult material to work with. As the properties of mica are not very well known even by optics companies, we offer a detailed overview in our materials section, including a table of physical properties of mica.

Some fast facts:

• Due to its natural cleavage, mica is suitable to produce accurate zero-order retarders at a much lower cost than any other base material.
  
• All our mica waveplates are zero order plates and as such can be used over a fairly broad wavelength range and a wide field of view., unlike the other types.
• Mica is transparent from approximately 350 nm to 6 µm, but not completely free of absorption.
• The mica sheet is extremely thin so in most cases it is laminated between protective glass plates for easy handling. But we have developed in-house technology for the reliable production of uncemented bare mica waveplates.
• Antireflection coatings for laminated and bare mica plates enhance transmission.
  
• Ring mounts are available as an option for easy system integration.