Yanchao Li

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%.

A method of second harmonic measuring glass thickness with ultra-precision based on multi-beam laser heterodyne

This paper puts forwards a novel method of second harmonic of multi-beam laser heterodyne measurement for the thickness of the glass, which is based on the combination of Doppler effect and heterodyne technology, loaded the information of the thickness to the frequency difference of the multi-beam laser heterodyne signal by frequency modulation of the oscillating mirror, which is in the light path. Heterodyne signal frequency can be obtained by fast Fourier transform, and can obtain values of the thickness accurately after the multi-beam laser heterodyne signal demodulation. This method is used for simulate values of different thickness of the glass through numerical simulation of MATLAB and the obtained result shows that maximal relative error is less than 0.02%.

Multi-beam laser heterodyne measurement with ultra-precision for the angle based on oscillating mirror sinusoidal modulation

This paper proposes a novel method of multi-beam laser heterodyne measurement for the angle. Based on Doppler effect and heterodyne technology, loaded the information of the angle to the frequency difference of the multi-beam laser heterodyne signal by sinusoidal frequency modulation of the oscillating mirror, which move as simple harmonic motion, this method can obtain many values of the angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, it can obtain the angle accurately. This novel method is used to simulate measurement for incident angle of standard plane mirror by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.49%.

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.