Research On Coherent Noise Suppression Technology Of High Precision Interferometer

With the wide application of optical products aerospace and military and other fields,the requirements for the detection accuracy of optical products have been improved.Therefore,many new methods and theories of high-precision measurement are emerging rapidly,which greatly improves the precision of optical precision measurement.Generally,high-precision measurements results can be given by interferometric.However,the accuracy of measurements will be affected by some factors in the process of interference,especially the coherent of system,which is bad for the results.Because the laser has a high coherence,when it passes through some optical components,a large number of coherent noise will appear in the interference images because of some drawbacks in the components.At present,experts from different countries have come up with variety of methods which can suppress the coherent noise of interference system and improve the measurement accuracy.Among these methods,the way of rotated frost glass is simple and easy,and it can be used in combination with a variety of methods.This method will not bring undesirable impacts to the optical system of the interferometer,and it has has been widely used by interferometers in the world.Based on the Fizeau interferometry,this aims to suppress the coherent noise in the interferometric system by using the rotated frost glass to improve the SNR of interference image and enhance the quality of the interference image.It not only avoids the optical system error,but also can be applied to a variety of interferometer.Therefore,a systematic and deep research has been studied on the influence of the rotated diffuser on the interference image quality.The main research contents are listed as follows:Firstly,the basic principles of Fizeau interference have been discussed.To be specific,the basic principle of interference fringes suppression was analyzed in detail.We delved into the optical modulation theory of frosted glass,including the theory of modulation of rough surface and rotation speed to laser beam.We also simulated the influence caused by surface roughness and rotation speed on noise suppression effect of interference image.Secondly,we built the noise suppression system based on Fizeau interference,and expounded the processing flow of the interference image.We also tested the influence caused by surface roughness and rotation speed on noise suppression effect of interference image and designed the correlation algorithm to calculate the fringe contrast of interference image,the noise contrast and image SNR,then compared them with the simulation results,and comparation showed good consistency.The experimental error was analyzed detailedly at the end of the paper.Finally,the results of simulation and experiment showed that when the noise reduction experiment was carried out in the interference system,the surface roughness and wavelength ratio of the frosted glass should be controlled in the range of 0.2 to 0.6.The frosted glass has good noise reduction performance and noise suppression.But in actual operation,we should properly reference the parameters of rotation speed,because the increase of the rotational speed of frosted glass can decrease the fringe contrast and the noise contrast of the interference image.When the rotation speed is at 50r/s,the image SNR is at its peak,which means the noise reduction effect of the interference image is in the best condition.