Fast and full range measurements of ellipsometric parameters using a 45° dual-drive symmetric photoelastic modulator

The fast and full range measurements of ellipsometric parameters ψ and Δ using a 45° dual-drive symmetric photoelastic modulator (PEM) are proposed. The PEM operates in a pure traveling modulation mode with a constant retardation magnitude and the modulation axis performing circular motion. A field programmable gate array is used to control the PEM and fulfill the data processing. The parameters sin 2ψ sinΔ, sin 2ψ cosΔ, and sin 2ψ can be measured simultaneously, providing accurate measurements of ψ and Δ over the full range. The experimental results show that the repeatability and sensitivity of this system are at 10^-3°, and the data acquisition rate is 1 ms/point.