Improvement of Wavelength Calibration Accuracy of Astronomical High-Resolution Spectrometers with Fabry-Perot Etalons
Hao Zhibo, Ye Huiqi, Tang Liang, Hao Jun, Han Jian, Zhai Yang, and Xiao Dong
Due to the wide wavelength coverage and dense transmission peak sequence of its spectrum, the Fabry-Perot etalon (FPE) for wavelength calibration of astronomical high-resolution spectra is expected to achieve higher calibration accuracy than traditional calibration sources. However, the unknown wavelengths of FPE transmission peaks pose a challenge for calibration. In this study, without precision measurement devices (such as Fourier transform spectrometers), the thorium-argon (ThAr) lamp, a conventional calibration source equipped on astronomical high-resolution spectrometers, was used to provide the FPE with wavelengths. Then, the errors in the ThAr wavelengths were corrected by using the dense transmission peak sequence of the FPE and the smooth relationship between the penetration depth of the dielectric reflective coating and the wavelength. Accurate wavelengths of the FPE transmission peaks were thus obtained, and wavelength calibration was performed. The calibration test on the fiber-fed high-resolution spectrometer of the Xinglong 2.16-m telescope showed that the wavelength calibration accuracy of the FPE reached 0.053 pm, which was significantly higher than that (0.290 pm) in the case of the ThAr being used alone.
  • Jan. 17, 2022
  • Acta Optica Sinica
  • Vol.42 Issue, 1 0112002 (2022)
  • DOI:10.3788/AOS202242.0112002
Research and Accuracy Verification of Linear Polarization Measurement Technology Based on Spectral Modulation
Shi jingjing, Hu Yadong, Li Mengfan, Liu Wuhao, and Hong Jin
The linear polarization measurement technology based on spectral modulation can modulate the polarization information of incident light to the spectral dimension through the spectral modulation module. The spectral modulation module is composed of a achromatic quarter-wave plate, a multiple-order wave plate and a polarization beam splitter, which can obtain the linear polarization and spectral information of the target in a single measurement. With the combination of modulation module and grating spectrometer, a dual-channel polarization measurement system is designed. The polarization measurement model of the system is derived, the influence of spectral broadening on the modulation spectrum is analyzed, and the partial periodic least squares curve fitting method is used to demodulate the polarization information. Moreover, a test device is built to verify the performance of the measurement system. First, the complete linear polarization light is used to calibrate the retardation of the multiple-order wave plate and the polarimetric efficiency of the system. Then, the polarization measurement accuracy of the system is verified by using the variable polarization light source. The experimental results show that maximum absolute deviation between the theoretical value and the measured value of degree of linear polarization of the variable polarization light source is 1.11%, and the maximum deviation of angle of linear polarization is 0.7°, which means the proposed system has high polarization measurement accuracy.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0212003 (2022)
  • DOI:10.3788/AOS202242.0212003
Radiometric Calibration Technology Based on Far Ultraviolet Hyperspectral Imaging Instrument
Xiao Si, Fu Liping, Hu Xiuqing, Pi Yanting, Jia Nan, Bai Xuesong, and Wang Tianfang
Using ultraviolet stars to finish the on-orbit calibration of far ultraviolet hyperspectral imaging spectrometer is an important step to achieve high precision remote sensing. However, in this way, the on-orbit calibration coefficients can not be directly used in target inversion. Therefore, the conversion of on-orbit calibration coefficients is of great significance to improve the on-orbit calibration accuracy of instrument. In this paper, the conversion process of the calibration coefficients is derived, a new equation of the calibration coefficients is given, the related verification experiments are carried out by using the developed instrument. The results show that the accuracy of target inversion can be improved by 40% by using the modified calibration coefficients.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0212002 (2022)
  • DOI:10.3788/AOS202242.0212002
Photoacoustic Detection Method for Depth of Surface Narrow Defects
Li Haiyang, Zhi Binliang, Pan Qianghua, An Zhiwu, and Yu Ruien
This paper develops a depth measurement theory related to defect width for the quantitative laser ultrasonic detection of surface defect depth. A depth measurement formula with a width correction item is established, and a concept of defect size ratio is defined. Defects are divided into three types, namely narrow defects, extremely narrow defects, and wide defects. The applicability of the defect depth measurement method in measuring the three types of defects is discussed, and finite element simulation is adopted for verification. Finally, an experimental platform for laser ultrasonic detection is built to conduct depth detection of aluminum alloy samples with surface defects. The results show that quantitative detection of narrow defect depth can be achieved by introducing the width correction item. The average measurement error is less than 5%, which means that accurate measurement of the defect depth has been achieved.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0212001 (2022)
  • DOI:10.3788/AOS202242.0212001
Research of Phase-Sensitive-Detection Algorithm Based on Adaptive Filtering
Lei Ming, Feng Zhihui, Nan Yaming, and Feng Tian
Incoherent laser off-target quantity detection relies on quadrature phase demodulation, and the application of a Kalman low-pass filter can significantly improve the phase discrimination performance of digital quadrature demodulation phasemeters. This paper proposes a solution based on Sage-Husa adaptive filtering, which uses adaptive factors to adjust the state prediction covariance array to effectively reduce the model errors and improve the filtering accuracy, to address the problem that the accuracy of the Kalman low-pass filter decreases when the noise statistics information is unknown. The adaptive Kalman filtering method may substantially improve the phase identification performance of a digital phase-locked demodulator and reduce the decoding error of off-target amount under low signal-to-noise ratio, according to Matlab simulation studies.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0112003 (2022)
  • DOI:10.3788/LOP202259.0112003
Calibration Method of Pinhole Aperture Attenuation in Reflectance Transfer Spectrometer
Jiang Feng, Niu Xinhua, and Yin Kai
A reflectance transfer spectrometer can be used to accurately and quickly calculate the spectral reflectance of the ground target from the measured spectral irradiances of the sun and ground, thus achieving the long-term stable-radiation standard transfer on-orbit. In this process, a pinhole aperture is used to largely attenuate sunlight for the direct imaging of the solar disk. The accuracy of the pinhole aperture attenuation factor directly determines the measurement and transfer accuracies of the reflectance. Based on the calibration principle of detector response nonlinearity using a laser, a method that combines the wide dynamic standard light source with a back spectrometer for comparison measurements is proposed for the high-accuracy calibration of the attenuation factor of a front pinhole aperture. Results show that the attenuation factor of the pinhole aperture shows obvious nonuniformity both in terms of the spatial and spectral dimensions. After modifying the experimental outdoor reflectance measurements, the relative difference of the measured spectral reflectance of the white diffusing plate can be reduced from 20% to less than 2%. This finding proves the validity of the laboratory calibration of the aperture attenuation factor and can provide a technical basis for the high-accuracy cross calibration of reflectance transfer spectrometers.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0112002 (2022)
  • DOI:10.3788/LOP202259.0112002
Micro Defect Detection of Steel Ball Surface Based on Spatial Omni-Directional Light Source
Feng Chao, Jiang Yi, and Zhao Xiaomeng
Aiming at the adverse effect of high reflection and high curvature of metal sphere on surface micro-defect detection, a detection method based on spatial omni-directional light source and image fusion is proposed. The image information is obtained by scanning the spherical surface through different illumination schemes provided by the spatial omni-directional light source system. Image fusion is used to accumulate the difference between micro defects and background in the effective detection area, enlarge the difference between micro defects and background, and improve the ability of micro defect detection. The experimental results show that the detection device based on the proposed method can detect the micro defects at different positions on the surface of bearing steel ball with a diameter of 20 mm and a precision of G16 significantly, and solves the problem of blind area caused by high reflection of metal sphere, and has good detection ability for various micro defects on the surface of bearing steel ball.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 2 0212002 (2022)
  • DOI:10.3788/LOP202259.0212002
Measurement of Wavefront Aberration of Lens Based on Phase Measuring Deflectometry
Gao Jinrui, Li Dahai, Lai Heng, Zhang Xinwei, Wang Ruiyang, and Ruan Yilang
In this paper, a model that regards lens with aberration as a combination of ideal thin lens and prisms array is proposed, which is dedicated to verify that the transmissive phase measuring deflectometry is feasible to measure the wavefront aberration of the lens. The simulation results of ZEMAX and Matlab verify that the wavefront aberration of lens obtained in raytracing and in reverse raytracing are approximately equal. Based on this conclusion, an experimental setup is built and the wavefront aberration of a single lens with an aperture of 75 mm is measured. The experimental results show that the method only needs a CCD camera and a LCD display to complete the measurement, which has the feature of simple equipment and easy operation without complicated calibration, providing a method for online measurement of wavefront aberration of the lens.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 2 0212001 (2022)
  • DOI:10.3788/LOP202259.0212001
Spatial-Temporal Combined Phase Unwrapping in Phase Measurement Profilometry
Hou Yanli, Liang Hangang, Li Fuqian, and Chen Wenjing
A spatial-temporal combined phase unwrapping method is proposed, which improves the noise suppression ability and phase unwrapping reliability of the three-frequency temporal phase unwrapping method. The fringes with sensitivity greater than 1 are used to replace the fringes with sensitivity of 1 in the traditional three-frequency temporal phase unwrapping method. By calculating the wrapped phases of these fringes, the spatial phase unwrapping of them is carried out, and the unwrapped phases are used to guide the unwrapping of the other two high sensitivity wrapped phase images. Compared with the traditional three-frequency temporal phase unwrapping method, the proposed method reduces the frequency multiple difference between the three sets of fringes when the spatial frequencies of the highest sensitivity fringes of them are the same, thus reducing the influence of noise on phase unwrapping and improving the reliability and accuracy of three-frequency temporal phase unwrapping.
  • Dec. 22, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 1 0112006 (2022)
  • DOI:10.3788/AOS202242.0112006
Three-Dimensional Face Modeling Based on Multi-Scale Attention Phase Unwrapping
Zhu Jiangping, Wang Ruike, Duan Zhijuan, Huang Yijie, He Guohuan, and Zhou Pei
Phase unwrapping plays an important role in three-dimensional (3D) measurement technologies, and its analytical accuracy directly affects the accuracy of 3D modeling. Due to undersampling and discontinuity of the wrapped phase, it is difficult to obtain correct phase information for traditional spatial phase unwrapping, while temporal phase unwrapping requires additional auxiliary information. For 3D face modeling in complex scenarios, a phase unwrapping network based on multi-scale attention is proposed in this paper. In this network, the encoder-decoder structure is used to fuse multi-scale features, and an attention sub-network is embedded into the decoding network for contextual information collection. A FACE dataset of 5000 samples and a MASK dataset of 100 samples are constructed, and each sample contains the truth values of wrapped phases and continuous phases for training and testing of phase unwrapping. The root-mean-square errors of the proposed network are 0.0387 rad and 0.0273 rad on the FACE dataset and the MASK dataset. The structural similarities are 0.9850 and 0.9793 respectively. The phase features can be extracted quickly and accurately in areas such as undersampled and phase discontinuous ones to ensure the correctness of phase unwrapping. Finally, the effectiveness and feasibility of the proposed network are verified by comparative experiments.
  • Dec. 22, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 1 0112005 (2022)
  • DOI:10.3788/AOS202242.0112005