Mr. Feng Guo Profile

Feng Guo

at National Univ of Defense Technology

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Proceedings Article | 18 December 2019 Paper

Study of lap-MRF process based on surface profile filtering for large aperture mirrors

Feng Guan, Hao Hu, Xin Li, Feng Guo, Tao Zhao

Proceedings Volume 11341, 113411S (2019) https://doi.org/10.1117/12.2547745

KEYWORDS: Mirrors, Polishing, Surface finishing, Magnetorheological finishing

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A Lap-MRF process is proposed for large aperture mirrors. In Lap-MRF, a lap is used to expand the polishing area, which improves the material removal rate. Moreover, the MR fluid can be renewed continuously to ensure the stability of the material removal rate, which improves the convergence efficiency of the surface profile error. In this paper, the figuring ability of the Lap-MRF removal function is analyzed. The Lap-MRF process, which is based on surface profile filtering, is presented. Finally, a series of figuring experiments on a Φ350 mm K9 mirror are carried out. For the Lap-MRF removal function, the volume removal rate is up to 0.48 mm³ /min and the cut-off frequency is about 0.03 mm^-1 . After four times figuring using Lap-MRF, the surface profile error throughout the whole surface is improved to 4.84 λ (λ= 632.8 nm) PV (Peak-to-Valley), 0.69 λ RMS (Root Mean Square) from 25.24 λ PV, 4.31 λ RMS and its total convergence ratio of the RMS error is up to 6.32. These results verify the validity of the proposed method for large aperture mirrors.

Proceedings Article | 19 September 2013 Paper

Damage effect on CMOS detector irradiated by single-pulse laser

Feng Guo, Rongzhen Zhu, Ang Wang, Xiang’ai Cheng

Proceedings Volume 8905, 890521 (2013) https://doi.org/10.1117/12.2034724

KEYWORDS: Pulsed laser operation, CMOS sensors, Laser damage threshold, Sensors, Laser energy, Charge-coupled devices, Electrodes, Imaging systems, Laser induced damage, CCD cameras

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Imaging systems are widespread observation tools used to fulfill various functions such as recognition, detection and identification. These devices such as CMOS and CCD can be damaged by laser. It is very important to study the damage mechanism of CMOS and CCD. Previous studies focused on the interference and damage of CCD. There were only a few researches on the interaction of CMOS and the laser. In this paper, using a 60ns, 1064 nm single-pulse laser to radiate the front illuminated CMOS detector, the typical experiment phenomena were observed and the corresponding energy density thresholds were measured. According to the experiment phenomena, hard damage process of CMOS can be divided into 3 stages. Based on the structure and working principle of CMOS, studying the damage mechanism of 3 stages by theoretical analysis, point damage was caused by the increase in leakage current due to structural defects resulting from thermal effects, half black line damage and black lines cross damage were caused by signal interruption due to that the device circuit fuses were cut. Enhancing the laser energy density, the damaged area expanded. Even if the laser energy density reached 1.95 J/cm², black lines has covered most of the detector pixels, the detector still not completely lapsed, the undamaged area can imaging due to that pixels of CMOS were separated with each other. Experiments on CMOS by laser pulses at the wavelength of 1064 nm and the pulse duration in 25ps was carried out, then the thresholds with different pulse durations were measured and compared. Experiments on CMOS by fs pulsed laser at the frequency of 1 Hz, 10 Hz and 1000 Hz were carried out, respectively, the results showed that a high-repetition-rate laser was easier to damage CMOS compared to single-shot laser.

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