Calibrations of Phase Modulation Amplitude of Photoelastic Modulator

Abstract

A multiple harmonic intensity ratio technique is proposed for calibrating the modulation amplitude (Á 0 ) of a photoelastic modulator (PEM). A data acquisition system is utilized to investigate the frequency response of this technique. Á 0 determined by this technique is independent of frequency, which is proved using the reflection and transmission setups. In addition to confirm our calibration using the digitized oscilloscope waveform, we also obtain a set of ellipsometric parameters under various values of Á 0 before and after calibration. We also introduce a correction factor to correct the effect caused by the shift of the modulation amplitude in the process of etching. An optical thick film is used to calibrate Á 0 using PEM ellipsometry, and its refractive index and extinction coefficient are also obtained in etching. Finally, we suggest the use of the traces of the ellipsometric parameters under various thicknesses for monitoring instead of calculating the thickness in real time.

The Development of Three-Intensity Measurement in PSA Ellipsometry and Photoelastic Modulation Ellipsometry

“…For monitoring the physical processes, plasma etching [16], deposition [17], thermal heating [18], and photo-induced [19], one has to establish the in situ alignment technique for PEM ellipsometry. A DAQ card is an analog-to-digital converter.…”

“…However, for Figure 21. Distributions of Ψ for film etched from 500-nm thickness of SiO 2 on silicon substrate (a) before calibration and (b) after calibration: (dotted line) theoretical value; (solid line) measured value  fc [16].…”

Dual-modulator broadband infrared Mueller matrix ellipsometry

“…One notices that the actual retardation, as determined by the calibration, is about 0.1 rad higher at that IR energy. The magnitude of this offset is typical for PEMs [56]. Calibration of the PEM controller front panel to match the actual retardation is not necessary, because it is the precise retardation at each wavelength that is required for processing the data.…”

Method for measuring retardation of a quarter-wave plate based on normalized secondary harmonic component

“…If the modulating frequency of the PEM is $ and the peak retardation is B 0 , the PEM's time-varying phase retardation has the following form [8]:…”