Abstract

We report phase retardance measurements of a liquid crystal (LC) based, electrically tunable wave plate as a function of applied voltage and incident optical intensity at 10.6 µm. Utilizing Stokes and Mac-Cullaugh ellipsometry, we distinguish twist effects of the LC director with respect to substrate surfaces from tilt effects off the surface. Thermal changes in birefringence determine device performance at intensities up to 900 W/cm² and not optically induced reorientation effects. The LC wave plate utilized a 25-µm thick parallel aligned layer of E7. Phase retardance and output polarization state azimuth angle were measured as a function of optical intensity. Absence of any statistically significant variation in measured azimuth angle as a function of the incident optical field strength demonstrates that the observed loss of phase retardance with increasing optical intensity is not the result of optically induced reorientation effects. Based on the 1-D theory of Deuling,¹ we have calculated the phase retardance of our LC cells up to 50°C. Agreement between theory and experiment clearly indicates that the dominant factor in the loss of retardance with increasing optical intensity is attributable to d(Δn)/dT.

© 1989 Optical Society of America