Spectroscopy|18 Article(s)
Baseline Fitting Algorithm of Spectral Signal Region
Cheng-bin YAO, Yun-wei JIA, Jiang-bo WU, Kun WANG, and Chen-xiang HAO
A baseline fitting algorithm for spectral signal region is proposed in order to eliminate the adverse effects of baseline distortion in spectral processing. First, a GradSuck fitting algorithm is proposed for baseline with abrupt curvature by using the idea of gradient inertia force and suction, which cover the shortage of the piecewise quadratic polynomial fitting algorithm when the baseline curvature around the signal area changes suddenly. Then this algorithm is combined with the piecewise quadratic polynomial fitting algorithm to propose a more general fitting algorithm for spectral signal region. At the same time, the proposed algorithm has been compared with different baselines fitting algorithms. Experiments under various baseline types with different SNR show that the baseline fitting algorithm of signal region has reliable accuracy and stability, and it can extract the spectral baseline better than other algorithms. The relative error of its whole fitting accuracy is only 47.0% of the quadratic polynomial fitting, 35.6% of the AirPLS fitting, and 20% of the wavelet fitting. And it also has high real-time performance because of only fitting the baseline of the signal region.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49 Issue 12 105 (2020)
Analysis of Influence of Spike on Phase Retrieval Accuracy of Doppler Asymmetric Spatial Heterodyne Spectrometer and Correction Method
Ting-ting YU, Yu-tao FENG, Di FU, Xuan WANG, Chen SUN, and Qing-lan BAI
The doppler asymmetric spatial heterodyne interferometer can be used to retrieve the atmospheric wind speed by measuring the phase frequency shift of interference fringes. Because of the interference from cosmic rays and “hot pixels” in CCD, some spikes that have random location and intensity occur on the interferogram. The presence of such spikes can seriously affect the accuracy of wind speed retrieval. In this paper, the theoretical influence of various parameters of spike on the phase inversion accuracy of doppler asymmetric spatial heterodyne interferometer is discussed, and the spike correction method is proposed. Based on the characteristics of the spike and the phase retrieval model of doppler asymmetric spatial heterodyne interferometer, a theoretical model between the phase error and the intensity and position of the spike is established. The influence of the intensity, position and width of the spike on the phase retrieval accuracy is analyzed and verified by experiments. The results show that the phase retrieval error varies periodically with the position of the spike, and is positively correlated with the intensity and peak width of spike. A new method of spike correction based on nearest neighbor comparison and windowed median filter is proposed. The new method can effectively correct the spike without affecting the original interference data. The phase error caused by the spike after correction is reduced by more than 90%, which will help to improve the accuracy of subsequent interference data processing.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49 Issue 12 83 (2020)
A Measurement Method Based on Characteristic Spectral Parameter for Determining Junction Temperature of LED
Fu-chun JIANG, Si-yu HE, Yuan-hai LIU, Wen LIU, Guang-yue CHAI, Zhi-gang ZHAO, and Bai-kui LI
Aiming at YAG white LED generated by blue-light excitation phosphor, a set of junction temperature measurement system based on characteristic spectral parameters is designed by using conventional visible spectroscopy and temperature control system through analyzing spectral trough characteristics. The measurement process is divided into two parts:the measurement of calibration function and the measurement of arbitrary state. Firstly, the relative luminescence spectra at different junction temperature and normal driving current are measured by spectrometer, and then the relative spectral intensity at the spectral trough is analyzed. Considering practicability and cost reduction, normal working current drive is adopted, but the self-heating effect of LED driven by normal working current can not be neglected in the fixed reaction time of spectrometer. Therefore, the selected reference state method is used to make the difference between the relative luminescence spectral intensity at each temperature and the reference state point by point to get the corresponding difference value. At the same time, in order to reduce the temperature deviation introduced by the temperature control system, the corresponding junction temperature difference is also obtained by making the difference between each temperature and the reference temperature. Experiments show that the calibration functions of junction temperature difference and luminescence spectral intensity difference of LED with high and low color temperature have high linearity, and R2 is above 0.99. Using the calibration function, the junction temperature of LED can be measured at any state. Finally, the junction temperature data of high and low color temperature LED obtained by the proposed method under different conditions are compared with the measurement results by T3Ster instrument of Mentor Graphics Company. The maximum deviation is 2.82%. Within the acceptable error range, it shows that the proposed method is completely feasible and has certain practical value.
Acta Photonica Sinica
  • Publication Date: Mar. 25, 2020
  • Vol. 49 Issue 3 0330003 (2020)
High Precision Temperature Control Design for TDLAS Gas Detection System
Xu LIU, Peng-shuai SUN, Xi YANG, Tao PANG, Hua XIA, Bian WU, Zhi-rong ZHANG, Zhi-feng SHU, and Chi-min SHU
According to the structure of gas cavity and the properties of optical components, an accurate circuit control method of constant temperature and stability control box is designed, and the high-precision stability control of multi-temperature state inside the box is realized.The temperature control system can be used to study the variation of gas temperature and gas absorption spectrum parameters, and improve the detection accuracy of gas concentration.The hardware circuit system including high-precision constant-current source, two-channel temperature sampling module and conditioning circuit, A/D analog-digital conversion circuit and semiconductor refrigerator control module is designed.The corresponding system software is developed to ensure the uniformity of the temperature of the optical cavity.According to the actual temperature control box parameters, with the proportional integral differential control algorithm as the core, the temperature change inside the optical cavity is precisely controlled, realizing the optimal temperature change control fluctuation inside the temperature control box is ±0.009 ℃ and the standard deviation is lower than 0.006 ℃.Temperature control experiments are carried out under seven temperature states of 16 ℃, 20 ℃, 24 ℃, 28 ℃, 32 ℃, 36 ℃ and 40 ℃ respectively using CO2 standard gas with a concentration of 2.00%. The stability of the temperature control system is verified through the measurement results.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49 Issue 12 93 (2020)
Multi-channel Raman Spectral Reconstruction Based on Gaussian Kernel Principal Component Analysis
Xin WANG, Zhe-ming KANG, Long LIU, and Xian-guang FAN
The multi-channel Raman imaging system is often affected by the nonlinear factors such as fluorescence background and noise, which reduces the Raman spectral reconstruction accuracy. Therefore, a reconstruction algorithm based on Gaussian kernel principal component analysis was proposed, in which the calibration samples are optimized by similarity factor; Then the calibration samples were mapped to high-dimensional space in a nonlinear form by using kernel function; The basis function was extracted from the mapped data set, and the basis function coefficients were obtained by pseudo-inverse method. Polymethyl methacrylate was used in the experiment and the Raman spectral reconstruction accuracy was evaluated in terms of relative root mean square error. The experimental results show that the proposed algorithm has higher reconstruction accuracy and anti-noise property than the traditional pseudo-inverse and wiener estimation methods. And the proposed algorithm can effectively reduce the impact of bad data and nonlinear factors in the calibration samples and imaging system. Therefore, the proposed algorithm can provide an effective Raman spectral reconstruction algorithm for multi-channel Raman imaging.
Acta Photonica Sinica
  • Publication Date: Mar. 25, 2020
  • Vol. 49 Issue 3 0330001 (2020)
Detection Method of Dissolved Oxygen Concentration in Water Based on Single Source Frequency Domain Fluorescence Lifetime
Peng CHEN, Zhi ZHAO, Dong-dong ZHAO, Yang-yang HAN, and Rong-hua LIANG
To reduce the complex optical path and circuit structure in optical dissolved oxygen concentration detection system, this paper proposes a methodology for detecting dissolved oxygen by frequency-domain fluorescence lifetime. The single-channel light source is used to detect the concentration of dissolved oxygen in water, which simplifies the optical path and circuit structure, improves the dissolved oxygen concentration detection algorithm and enhances the efficiency of inspection process. The effectiveness of the method is evaluated. Comparing with the results from an optical dissolved oxygen analyzer, our proposed method performed better in terms of the detection error (reduced from 0.1 mg/L to 0.04 mg/L in the range of 0~9 mg/L) and the stability (the standard deviation is decreased by 36% to 0.007 mg/L). Leveraging the implementation of a fast Fourier transform-based algorithm, the response time was reduced by an average of 12 seconds as steady state reached 90%, the response speed was increased to the percentage of 40% at the rise of concentration and 28% at the fall of concentration separately. The methodology demonstrated the effectiveness of detection accuracy, stability and response speed.
Acta Photonica Sinica
  • Publication Date: Mar. 25, 2020
  • Vol. 49 Issue 3 0330002 (2020)
Experimental Study of Radiometer Based on Spontaneous Parametric Down-conversion Calibration
You-bo HU, Dong-yang GAO, Jian-jun LI, and Xiao-bing ZHENG
The spectral distribution and time correlation of spontaneous parametric down-conversion were measured, and a radiometer based on spontaneous parametric down-conversion calibration was established. Based on the detection efficiency of spontaneous parametric down-conversion calibration, a radiance measurement scheme in terms of photon count was proposed, the radiometer can correct the degradation of its own response and observe the radiance of the target in real time. By using the experimental technique of inserting optical attenuator and changing detectors, the radiometer can correct its own degradation if observed radiance measurement results under the condition of optical degradation and electronics degradation. The results show that the consistency of observed radiance can meet 0.4%.The measurement results provide experimental basis for the application of spontaneous parametric down-conversion calibration to space platforms.
Acta Photonica Sinica
  • Publication Date: Jun. 25, 2020
  • Vol. 49 Issue 6 0630001 (2020)
Cross Interference Characteristics of Photoacoustic Spectroscopy Multi-gas Analyzer
Shuai YUAN, Guangzhen WANG, Dehui FU, Ke CHEN, Ran AN, Bo ZHANG, Min GUO, and Guangyin ZHANG
A photoacoustic spectroscopy multi-gas detection system based on infrared heat radiation light source was developed. The broadband mid-infrared thermals radiation source and band-pass filter were used to generate the photoacoustic excitation light. Combined with a small-volume non-resonant photoacoustic cell, the time-sharing measurement of multi-component gas concentration was realized. The parameters of the mid-infrared bandpass filter were determined by analyzing the main factors of cross-interference among multi-component gases and the infrared absorption spectrum of target gases. To determine the quantitative relationship of cross interference among the gases to be measured, the photoacoustic spectrometer system was calibrated by using the standard gas, and a humidifier was used to analyze the interference from water vapor. The experimental results showed that the interference levels of C2H2 to CH4 and CH4 to C2H6 reached 10.49 μV/(μL/L) and 18.66 μV/(μL/L) respectively, and the interference between other hydrocarbon gases can be ignored. The responsiveness of CO2 to CO, CH4, C2H2 and C2H4 interference was 1.615 μV/(μL/L), 0.055 μV/(μL/L), 0.130 μV/(μL/L) and 0.016 μV/(μL/L), respectively. In addition, water vapor will cause certain interference to C2H2, CH4, C2H6, C2H4, CO and CO2, and the responsiveness of the interference was 0.591 μV/(μL/L), 0.421 μV/(μL/L), 0.071 μV/( μL/L), 0.007 μV/(μL/L), 0.051 μV/(μL/L) and 0.055 μV/(μL/L). The experimental results indicated that there was a high level of interference when detecting CH4 in C2H2 background, C2H6 in CH4 background, CO in CO2 background, and other target gases in high concentration water vapor background, which should be considered in the measurement process.
Acta Photonica Sinica
  • Publication Date: Apr. 25, 2021
  • Vol. 50 Issue 4 198 (2021)
Quantitative Modeling for Earth Sample's LIBS Spectra of Curiosity Rover Based on Inception Network
Le-hao ZHANG, Li ZHANG, Zhong-chen WU, Cheng-jin ZHANG, Zong-cheng LING, Liang HAN, and Xue-qiang CAO
The traditional multivariate analysis method is the main method for quantitative modeling of LIBS spectral datasets, but the input dimension of the spectrum is relatively high. Reducing the dimension of the spectrum and extracting the characteristic spectral line in advance is needed by many algorithms, which results in partial loss of information and affects the accuracy. Aiming at this issue, a quantitative modeling method based on deep convolutional neural network inception is introduced, and the conventional 2D convolutional network is transformed into 1D form to realize full spectrum input and feature extraction of spectral information. Not only there is no need to reduce the dimension of the original spectrum in this method, but also it omits other preprocessing operations such as filtering. Through many experiments, when the number of training is 2 000, it has a good prediction result with no obvious overfitting phenomenon. Its average coefficient of determination (R2) is 0.957 9, and its root mean square error is reduced to 61.69% of those by Partial Least Squares Regression (PLSR). Compared with PLSR and the AlexNet deep learning method the proposed method both gets better results.
Acta Photonica Sinica
  • Publication Date: Jun. 25, 2020
  • Vol. 49 Issue 6 0630002 (2020)
Establishment and Optimization of Photoacoustic Cell Model in Photoacoustic Spectrum Detection System
Nan ZHAO, Yang LIU, Ningyang ZHAO, Longge MA, Meicong LI, Jingjing JIAO, and Chenfei DING
The photoacoustic cell, as the core component of the photoacoustic spectroscopy gas detection system, directly affects the detection accuracy of the system. Based on the classic cylindrical photoacoustic cell, the finite element analysis software is used to combine the two physics of pressure acoustics and thermoviscous acoustics and build a model to simulate the acoustic-thermal coupling process in the photoacoustic cell. The effect of different geometric parameters of the resonant cavity and buffer cavity on the performance of the photoacoustic cell is compared through simulation, and then, the optimal size is determined. The simulation results show that the length and radius of the resonant cavity and the buffer cavity will affect the resonance frequency and acoustic pressure. After fully considering the comparison results and the difficulty of industrial manufacturing, the optimal length of the resonant cavity is selected as 120 mm, the optimal radius is 3 mm, and the buffer cavity radius is 35 mm. On this basis, a photoacoustic cell with a rounded connection between the resonant cavity and the buffer cavity is designed. Compared with the right-angle photoacoustic cell with the same size, the round-corner photoacoustic cell has more advantages in improving the photoacoustic signal and reducing the flow noise interference. The quality factor is increased to 1.109 times, the cell constant is increased to 3 635.1 Pa·cm/W, and the acoustic pressure is increased to 1.26×10-5 Pa. In the concentration detection of methane gas, the system sensitivity can reach 0.87 ppm, and the detection result is ideal, which meets the requirements of high sensitivity. Therefore, the performance of the round-corner photoacoustic cell has been significantly improved, which can provide a reference for the optimal design of the photoacoustic cell.
Acta Photonica Sinica
  • Publication Date: Jul. 25, 2021
  • Vol. 50 Issue 7 238 (2021)