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F. Bammer, R. Petkovsek, J. Mozina, J. Petelin:
"A Small and Fast SCPEM-Based Ellipsometer";
Poster: Photonics West 2010, San Francisco, USA; 01-26-2010 - 01-28-2010; in: "Proceedings of SPIE, Optical Components and Materials VII", SPIE-Proceedings, Vol. 7598 (2010), ISBN: 9780819479945; 75981T-1 - 75981T-8.

We propose a small and fast ellipsometer with a basic layout similar to that of conventional ellipsometers using photo-elastic modulators (PEM) oscillating with 50 kHz. A conventional PEM is rather large, ~10 x 20 x 100mm, since it consists of one piece of glass and an actuator. Both parts are carefully adjusted to the desired frequency and then glued together. We replace such a standard modulator by a 127 kHz Single Crystal Photo-Elastic Modulator (SCPEM), a LiTaO3-crystal with a size of 20.6 x 7.5 x 5mm. The polarization of light that travels through this crystal is strongly modulated. The modulated light is reflected from the sample, passes a polarizer and hits a detector. Its signal is split into the dc-value and the amplitudes of the 1st and 2nd harmonic of the modulation frequency. These values lead via simple formulas to the ellipsometric parameters. Usually a Lock-In-Amplifier is used here, whereas we propose an automated digital processing based on a fast analog to digital converter controlled by a highly flexible Field Programmable Gate Array (FPGA). This and the extremely compact and efficient polarization modulation allow fast ellipsometric measurements as needed in high volume manufacturing of optics.

Ein kleines schnelles Ellipsometer zur Qualitätskontrolle in der Produktion

photo-elastic modulators, LiTaO3, ellipsometry

http://dx.doi.org/10.1117/12.841690