Linear birefringence measurement at 157 nm

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Abstract
The author describes a linear birefringence measurement instrument designed for the new optical lithography wavelength—157 nm. This instrument contains a deuterium lamp with magnesium fluoride window, a monochromator, a polarizer-photoelastic modulator(PEM) combination, a PEM-polarizer combination, and a photomultiplier tube. The sample is placed between the two PEMs. For measuring linear retardation, the signals carried on the first harmonics of the two PEMs are analyzed using lock-in amplifiers. A computer program calculates and displays both the retardation magnitude and angle of fast axis. The instrument reported here is a special polarimeter designed for measuring linear retardation in high quality optical components at 157 nm and other deep-ultraviolet wavelengths. It provides a retardation sensitivity of 0.01 nm at 157 nm.
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