A polarimeter using two photoelastic modulators

Abstract

We describe in this paper a special polarimeter for measuring linear birefringence in transparent optical samples. The polarimeter employs two photoelastic modulators that operate at different frequencies (50 KHz and 60 KHz). The resulting electronic signal at the detector is processed using two methods: demodulation by lock-in amplifiers or using Fourier analysis of a digitized waveform. We compare the results obtained by using the two signal processing methods in this special polarimeter and discuss how each method benefits selected applications.