Haifang Cong

The method for dual-beam laser heterodyne ultra-precision measurement of the glass thickness

A method for measuring thickness of glass is proposed based on laser heterodyne measurement and Doppler measurement, the largest error of simulation results is 0.8%.

Optimum Optical Local Oscillator Power Levels Impact on Signal-to-Noise Ratio in Heterodyne

The optical local oscillator power which makes the maximized signal-to-noise ratio is analyzed. Aiming at photovoltaic detector, the optimum optical local oscillator power is researched, and the theoretic value of optimum optical local oscillator power is acquired, and takes some experimental research basing on the theory.

A new method of estimating null time in ellipsometry

A new method which can estimate the null time in the ellipsometry is developed in order to measure precisely the thickness and refractive index of thin film. Ten images are taken consecutively at the null time during the measurement, and ten sets of (Pi, Ai) value for the images are obtained. The gray scale matrices of different images are analyzed and transformed, then the real values of the (Pi, Ai) for the sample are determined. Distribution of the thickness and the refractive index of the sample are presented. The measurement accuracy for thickness and refractive index are 1nm and 0.01, respectively.