Polymeric sheets as phase retardation elements

The spectral dependences of the retardance and the birefringence for 3 polymeric sheets of polyethylene, polyamide and polyethylene - polyamide blend between 420 and 680 nm have been studied. Retardance measurements were carried out using a recently developed model which allows for calibrating 2 phase plates simultaneously from a single adjustment of the optical system. A new parameter that expresses the retardance introduced when light crosses 1 mu m of the material is found to be useful in characterizing birefringent materials, and in constructing phase plates (for use at single wavelengths) and achromatic phase plates. (Original abstract)