Citation: | Zhang Jiaying, Wang Hongjun, Zhu Xueliang, et al. Effect of speed of rotated diffuser on image quality of interference fringes[J]. Opto-Electronic Engineering, 2018, 45(1): 170492. doi: 10.12086/oee.2018.170492 |
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Overview: In the interference system, the defects of the optical elements on the surface became a new light source, and coherent noise was generated under the irradiation of the laser beam. Then, a Newton ring and a bull’s-eye would be formed. They would affect the quality of the interfereogram acquisition, further influence the subsequent of interference image processing, and bring the measurement error. These coherent noises which influenced the interference results were the intrinsic noise of the system. The intrinsic noise were a difficult problem when the interferometer was designed. Therefore, experts and scholars made a lot of efforts in order to suppress the intrinsic noise. This paper mainly analyzed the noise reduction performance of rotated diffuser in Fizeau interferometer, and analyzed the relationship among the speed of diffuser and the SNR , contrast of speckle, contrast of fringe in order to improve the quality of interference images.
In order to cope with the coherent noise existing in the interferometric system, the rotated diffuser was adopted to suppress the coherent noise. The relative relationship among the contrast of fringe, speckle contrast , the SNR and rotated diffuser speed on the quality of the interfering image were obtained. Then, the control parameters of rotated diffuser would be required in the interference fringe through the verification experiment. The interference images were obtained under different control parameters. With the speed of the rotated diffuser increased, the relative contrast of the speckle, the fringe contrast and the SNR of the interference images were analyzed. And a good consistency was shown through the simulation results.
According to the measurement principle, we set up the Fizeau interference experiment system. The time delay of test light and reference light in interfering the system is τRT = 5×10-8, detector acquisition period T = 1/714 s, circular pupil diameter (entrance pupil diameter) D = 7 mm and wavelength λ = 650 nm. Assume that the angular velocity of the rotated diffuser is ω = 2πf, where f is the rotational speed of the diffuser, r = 20 mm, z = 35 mm.
The experimental results showed that it was rotated diffuser that could suppress the noise of the system in the interfering system significantly. With the speed of the rotated diffuser increased, meanwhile, the fringe contrast of the images would be decreased. However, the SNR would be improved. It is indicated that the rotated diffuser did have the effect of suppressing coherent noise. It provided the basis for the processing design of the diffuser in the interferometer, so as to realize the high-precision surface inspection.
Fizeau interferometer with rotated diffuser
The rotated diffuser
Fizeau interference system with rotated diffuser. 1. TF; 2. RF; 3. Expansion lens; 4. BS; 5. Laser; 6. Rotated diffuser; 7. Imaging lens; 8. CCD; 9. Speed control device
The influence of rotation frequency on image quality. (a) The influence to the fringes contrast; (b) The influence to the speckles images; (c) The influence to SNR
The relationship between rotated diffuser and the parameters; (a) The influence to the contrast of contrast; (b) The influence to the speckles images; (c) The influence to SNR of the fringes
The interference images at different speeds of the rotated diffuser. (a) f=10 r/s; (b) f=20 r/s; (c) f=30 r/s; (d) f=40 r/s; (e) f=50 r/s; (f) f=60 r/s; (g) f=70 r/s; (h) f=80 r/s