Variable birefringent beam splitter.

A sapphire disk is used as a variable birefringent beam splitter for the linearly polarized pump beam in an oscillator-amplifier dye laser system. Rotation of the disk varies the extent of retardation. The induced elliptical polarization results in a variable back surface reflectance between approximately 0.02-0.15 for the green spectral region. Reflectances are measured on two disks with different thicknesses and compared with an approximate model describing the reflectance as a function of angle of rotation of the disk.