A previously reported two-reflection, undeviating-beam total internal
reflection (TIR) quarter-wave phase retarder is optimized. The specifi
cations and characteristics of the device are sensitive to the refract
ive index n of the rhomb material. In particular, the size of the rhom
b can he reduced by a factor of 11 for the same aperture size if a gla
ss with n = 1.70 is used instead of one with n = 1.53, Optimal conditi
ons are in the refractive-index interval n = 1.68-1.71. Coated rhombs
of this type are mentioned.