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Retarder Sheets are clear birefringent materials that change the phase of a polarized beam of light. As light enters the retarder, it is separated into two components, one parallel to the axis and the other perpendicular. Upon passing through the sheet, light polarized in one direction is shifted in phase relative to light polarized in the perpendicular direction. By controlling the magnitude of birefringence and the thickness of the retarder, various amounts of phse shift (retardation) are introduced in one wave with respect to the other.

The relationship between retardation angle, δ, birefringence Δn, thickness of the sheet τ, and
wavelength of light λ is:

A quarter wave retarder has a phase shift of 90˚. That is Δnτ = λ/4. For wavelength λ at the center
of the visible region (550nm), a quarter wave film would have Δnτ = 138nm.

A quarter wave film can be used to convert linearly polarized light to circularly polarized light.

A half wave retarder can be used to rotate the plane of polarization 90˚.

The films are clear with transmittance of 92% (4% reflection occurs on each of the front and back surfaces). Phase uniformity is better than 8% over the entire file