Artifactual circular dichroism effect in a photoelastic modulator

The three-intensity technique is used to calibrate a photoelastic modulator by its temporal waveform. This method not only allows us to measure the intrinsic static phase retardation and modulation amplitude but also provides the evidence for the existence of circular dichroism (CD) in the photoelastic modulator. In this report, we will demonstrate the averaged intensity for normalization in this PEM modulated light not only depicts a periodic modulation, it also exhibits anti-symmetric distributions at P = 45° and P = −45°, which was considered as constant for conventional PEM ellipsometry. Four models were examined to verify that only a circular dichroism medium coupled with the periodical induced birefringence modulator can explain the phenomena. This work can quantitatively measure the artifactual CD effect of PEM and reduce its system error in CD spectrometer which consists of a PEM.