AUTOMATED SPATIALLY SCANNING ELLIPSOMETER FOR RETARDATION MEASUREMENTS OF TRANSPARENT MATERIALS

A highly sensitive and automated technique has been developed for meas uring the birefringence in transparent optical materials. The spatiall y scanning modulated transmission ellipsometer maps the birefringence of a transparent material by probing it with a polarization-modulated He-Ne laser beam. Computer-controlled voltage biasing of a Pockels cel l permits self-calibration and background subtraction of the system re tardance. The technique is capable of resolving differential retardanc es as small as 0.1 nm (lambda/6328) through a range of +/-lambda/2, wh ere lambda = 632.8 nm. Samples typically range in size from 50 mum to 10 cm in diameter within the sample plane and as much as 400 mm along the optical axis.