Since the coherent noise in the interferometric system, the method of rotated diffuser would reduce the coherence of the light beam to suppress the noise of the interference image. By analyzing the coherent noise reduction characteristics of rotated diffuser with different surface roughness, the relationship between surface roughness and the noise contrast under different rotation speeds was simulated, and the effective roughness range with noise reduction effect would be selected. It would build a noise reduction system based on Fizeau interference, and collected and calculated the noise contrast of the interference image. The effective range of σh/λ was 0.2~0.5 when the rotation speed was 10r/s, while the effective range of σh/λ was 0.4~0.6 when the rotation speed is 100r/s. The experimental results showed that the surface roughness and wavelength ratio σh/λ of rotated diffuser increased when the noise contrast tended to 1, but the effective range of surface roughness decreases with the increase of the rotational speed of the diffuser.
In order to improve the measurement accuracy of the laser displacement sensor, the laser triangulation displacement measuring system is established. The spot subdivision location algorithms of the system are studied, such as the Gaussian curve fitting, traditional gray weighted centroid and gray square weighted centroid. First, according to the principle of laser triangulation, the displacement measuring system is built. Then, objects are moved by the high-precision motorized stage, obtaining multiple sets of image data. Next, these data respectively are processed by the above several algorithms to obtain the corresponding coordinates of the laser spot, the system is calibrated respectively. Finally, comparing the displacement of calibration results calculating with the actual displacement. The results show that: those data that are processed by the gray square weighted centroid are used to calibrate , calculating the minimum error, and is 71.1 μm. It concludes that gray square weighted centroid is an ideal location segmentation method, which is not only simple and easy to implement, but also has a higher positioning accuracy.
Since the coherent noise affected the quality of the Fizeau’s interferograms in the large aperture, the coherence of the beam was changed by rotated diffuser to reduce the noise of the interfering system. The relationships between the frequency of the rotated diffuser, the contrast of the fringes and the SNR of the system were simulated. Then, the control parameters of rotated diffuser would be required in the optimum interference fringe. The interference images were obtained under different control parameters, and the fringe contrast and system SNR of each image were analyzed. The results showed that the contrast can be reduced by choosing the proper frequency of the rotated diffuser in a certain extent, but the SNR can be improved effectively and it was convenient to process the interference image later.
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