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%.