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Spectroscopy|378 Article(s)
Indoor CO2 Online Monitoring Based on Open-Path Tunable Diode Laser Absorption Spectroscopy
Qi Huang, Qing Wang, Kaitao Wang, Congshan Wang, Ruyue Cui, Hongpeng Wu, and Lei Dong
To investigate the variation in indoor carbon dioxide (CO2) volume fractions and their relationship with human activities, this study designs an open-path tunable diode laser absorption spectroscopy (TDLAS) sensing system to monitor indoor CO2 volume fractions. A distributed feedback (DFB) laser with a central wavelength of 2004 nm is employed as the excitation light source to measure the R(16) characteristic absorption line of carbon dioxide. The Levenberg-Marquardt method of nonlinear least squares fitting is employed to fit the measured spectra, allowing for volume fraction measurements without requiring calibration. Comparative measurements with a commercial XENSIVTM PAS CO2 sensor yield a high correlation (R2=0.89). The results indicate that the daily average indoor CO2 volume fraction is 4.63×10-4, slightly surpassing outdoor levels, whereas the fluctuation range of indoor CO2 volume fraction within a day is 3.86×10-4?5.66×10-4. Indoor CO2 volume fraction is volume fractions influenced by ventilation and indoor human activities, and the daily volume fraction trends are highly correlated with working hours. At a personnel density of 0.005 persons/m3, the growth rate of CO2 volume fraction is measured at 2.3×10-5 h-1. Therefore, timely ventilation is recommended for crowded indoor environments to prevent elevated CO2 volume fractions that may cause discomfort. To investigate the variation in indoor carbon dioxide (CO2) volume fractions and their relationship with human activities, this study designs an open-path tunable diode laser absorption spectroscopy (TDLAS) sensing system to monitor indoor CO2 volume fractions. A distributed feedback (DFB) laser with a central wavelength of 2004 nm is employed as the excitation light source to measure the R(16) characteristic absorption line of carbon dioxide. The Levenberg-Marquardt method of nonlinear least squares fitting is employed to fit the measured spectra, allowing for volume fraction measurements without requiring calibration. Comparative measurements with a commercial XENSIVTM PAS CO2 sensor yield a high correlation (R2=0.89). The results indicate that the daily average indoor CO2 volume fraction is 4.63×10-4, slightly surpassing outdoor levels, whereas the fluctuation range of indoor CO2 volume fraction within a day is 3.86×10-4?5.66×10-4. Indoor CO2 volume fraction is volume fractions influenced by ventilation and indoor human activities, and the daily volume fraction trends are highly correlated with working hours. At a personnel density of 0.005 persons/m3, the growth rate of CO2 volume fraction is measured at 2.3×10-5 h-1. Therefore, timely ventilation is recommended for crowded indoor environments to prevent elevated CO2 volume fractions that may cause discomfort.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0530004 (2024)
Evaluation of T91 Steel Aging Grade Based on Portable Laser-Induced Breakdown Spectroscopy Device
Weiye Lu, Meirong Dong, Kaijie Bai, Zihan Shang, Zhichun Li, Xiaoxuan Chen, Junbin Cai, and Jidong Lu
Microstructure and mechanical properties of heat-resistant steel will deteriorate during the service process. The real-time monitoring of the aging state is of great significance for safe operation and production. In this study, a portable laser-induced breakdown spectroscopy (LIBS) device is used to quickly diagnose the aging grade of T91 steel, while the obtained spectral features are dimensionally reduced and the modeling method is optimized. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to optimize and simplify the spectral features. Finally, after dimensionality reduction, the data are used to evaluate the aging grade model based on the K-nearest neighbor and the support vector machine (SVM) algorithms. Further, the influence of key parameter selection on the model performance is studied. The results show that the spectral data reduced by LDA can achieve a better clustering distribution and improve the accuracy of the evaluation model. In addition, the LDA-SVM model can achieve 94.58% accuracy, which is the highest among all the mentioned aging grade evaluation models. The result demonstrates that the modeling method can efficiently realize the aging grade evaluation of T91 steel based on portable LIBS. Microstructure and mechanical properties of heat-resistant steel will deteriorate during the service process. The real-time monitoring of the aging state is of great significance for safe operation and production. In this study, a portable laser-induced breakdown spectroscopy (LIBS) device is used to quickly diagnose the aging grade of T91 steel, while the obtained spectral features are dimensionally reduced and the modeling method is optimized. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to optimize and simplify the spectral features. Finally, after dimensionality reduction, the data are used to evaluate the aging grade model based on the K-nearest neighbor and the support vector machine (SVM) algorithms. Further, the influence of key parameter selection on the model performance is studied. The results show that the spectral data reduced by LDA can achieve a better clustering distribution and improve the accuracy of the evaluation model. In addition, the LDA-SVM model can achieve 94.58% accuracy, which is the highest among all the mentioned aging grade evaluation models. The result demonstrates that the modeling method can efficiently realize the aging grade evaluation of T91 steel based on portable LIBS.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0530003 (2024)
Information Encryption Based on Laser-Induced Breakdown Spectroscopy
Xiang Han, Lixing Yao, xin Zhang, Xiangyang Tian, Xing Su, Jinliang Lou, and Li Shen
In order to satisfy the requirements of information encryption security in the information era, this paper presents a method of information encryption based on laser-induced breakdown spectroscopy (LIBS) technology. The information to be encrypted was written on white paper with an aqueous solution prepared from zinc gluconate tablets and deionized water. By analyzing the LIBS spectra of white paper and of white paper coated with aqueous zinc gluconate solution, the spectral lines of Zn I at 328.23 nm, 472.22 nm, and 481.05 nm were used to decrypt the information. The LIBS spectra of different positions on the white paper containing the encrypted information were obtained by scanning, and the contrast of the spatial distribution of spectral intensity was improved by baseline correction, normalization, and spectral superposition, allowing the encrypted information to be interpreted more clearly and completely. The experimental results show that this method achieves efficient extraction of hidden information with zinc gluconate tablets commonly used in daily life, and has the advantages of high security, low cost, and convenient production. It provides a new idea for LIBS in the field of information encryption, and has value for certain potential applications. In order to satisfy the requirements of information encryption security in the information era, this paper presents a method of information encryption based on laser-induced breakdown spectroscopy (LIBS) technology. The information to be encrypted was written on white paper with an aqueous solution prepared from zinc gluconate tablets and deionized water. By analyzing the LIBS spectra of white paper and of white paper coated with aqueous zinc gluconate solution, the spectral lines of Zn I at 328.23 nm, 472.22 nm, and 481.05 nm were used to decrypt the information. The LIBS spectra of different positions on the white paper containing the encrypted information were obtained by scanning, and the contrast of the spatial distribution of spectral intensity was improved by baseline correction, normalization, and spectral superposition, allowing the encrypted information to be interpreted more clearly and completely. The experimental results show that this method achieves efficient extraction of hidden information with zinc gluconate tablets commonly used in daily life, and has the advantages of high security, low cost, and convenient production. It provides a new idea for LIBS in the field of information encryption, and has value for certain potential applications.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0530002 (2024)
Terahertz Spectral Anharmonicity of ANPZ Under Heating
Chai Xie, Yongwei Duan, Quancheng Liu, Hu Deng, Qi Zhang, Zhixiang Wu, Wenqing Wei, and Liping Shang
One of the benefits of using terahertz (THz) spectra in characterizing weak interactions is that their anharmonicity can help us to understand the macroscopic properties of crystals. In this study, 2,6-diamino-3,5-dinitropyrazine (ANPZ) was adopted to analyze the anharmonic mechanism of terahertz spectra. First, the temperature-induced anharmonicity was obtained from the THz spectral measurement under heating. Next, density functional theory was used to identify the vibration properties of each absorption. Vibration mode decomposition was then employed to deeply analyze the origins of these anharmonic differences. The results show that the softening of the special intermolecular hydrogen bonding is responsible for the strong anharmonicity. Furthermore, the displacement properties of the atomic temperature factor calculated based on phonon and quasi-simple harmonic approximations also verify the above conclusion. The present study demonstrates that THz spectroscopy can provide insight into the response of hydrogen bonding under heating and can be used as a scientific analysis method for understanding the macroscopic properties of crystals. One of the benefits of using terahertz (THz) spectra in characterizing weak interactions is that their anharmonicity can help us to understand the macroscopic properties of crystals. In this study, 2,6-diamino-3,5-dinitropyrazine (ANPZ) was adopted to analyze the anharmonic mechanism of terahertz spectra. First, the temperature-induced anharmonicity was obtained from the THz spectral measurement under heating. Next, density functional theory was used to identify the vibration properties of each absorption. Vibration mode decomposition was then employed to deeply analyze the origins of these anharmonic differences. The results show that the softening of the special intermolecular hydrogen bonding is responsible for the strong anharmonicity. Furthermore, the displacement properties of the atomic temperature factor calculated based on phonon and quasi-simple harmonic approximations also verify the above conclusion. The present study demonstrates that THz spectroscopy can provide insight into the response of hydrogen bonding under heating and can be used as a scientific analysis method for understanding the macroscopic properties of crystals.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0530001 (2024)
Research on the Evaluation of Target Camouflage Effect in Visible Spectrum Based on Similarity
Mengwei Shi, Junhua Yan, Guoyue Xu, Yin Zhang, Xutong Hu, and Qi Qian
The comprehensive similarity between the camouflage target and the background can measure the feature difference between the camouflage target and the surrounding background. The higher the comprehensive similarity, the higher the fusion degree between the target and the background, and the higher the camouflage efficiency of the target. In this paper, seven typical features of target and background images, including brightness, color, texture, shape, size, structure, and histogram, are used to represent the camouflage characteristics of the target. The corresponding similarity measurement method is used to obtain the similarity of each feature. The entropy weight method is used to objectively determine the weights of different feature indicators, and the comprehensive similarity between the camouflage target and background is obtained by linear weighting. Thus, the quantitative evaluation results of target camouflage effectiveness can be obtained. Multiple experiments under different backgrounds, different reconnaissance distances and different target attitudes show that the comprehensive similarity between the camouflage target and the background proposed in this paper is consistent with the target discovery probability, consistent with the detection distance, and robust to the background, which proves the correctness and effectiveness of the proposed method. The reliability of the proposed method is proved by comparison experiment. The comprehensive similarity between the camouflage target and the background can measure the feature difference between the camouflage target and the surrounding background. The higher the comprehensive similarity, the higher the fusion degree between the target and the background, and the higher the camouflage efficiency of the target. In this paper, seven typical features of target and background images, including brightness, color, texture, shape, size, structure, and histogram, are used to represent the camouflage characteristics of the target. The corresponding similarity measurement method is used to obtain the similarity of each feature. The entropy weight method is used to objectively determine the weights of different feature indicators, and the comprehensive similarity between the camouflage target and background is obtained by linear weighting. Thus, the quantitative evaluation results of target camouflage effectiveness can be obtained. Multiple experiments under different backgrounds, different reconnaissance distances and different target attitudes show that the comprehensive similarity between the camouflage target and the background proposed in this paper is consistent with the target discovery probability, consistent with the detection distance, and robust to the background, which proves the correctness and effectiveness of the proposed method. The reliability of the proposed method is proved by comparison experiment.
Laser & Optoelectronics Progress
- Publication Date: Feb. 25, 2024
- Vol. 61, Issue 4, 0430001 (2024)
Development and Prospects of Spectral Reduction Technology of Echelle Spectrometer (Invited)
Tao Cui, Lu Yin, Pei Liang, Yanan Sun, and Le Wang
The echelle spectrometer is a major spectroscopic instrument with its high spectral resolution in a wide range of applications. The spectral reduction technique is the core of the data processing of the echelle spectrometer, which realizes the rapid reduction of two-dimensional images to one-dimensional spectra by establishing the correspondence between wavelength and imaging position. The performance of the echelle spectrometer is directly determined by the accuracy of spectral reduction, which is the most important point and greatest difficulty in instrument development. In view of this, the development of the spectral reduction technique is reviewed, and its evolution is classified into three stages: ray tracing, modeling, and calibration methods. The core ideas and principles of spectral reduction algorithms in each stage are discussed in detail. Finally, the development history is summarized, the development trend is predicted, and the outlook of the development direction for the echelle spectrometer spectral reduction technology is discussed. The echelle spectrometer is a major spectroscopic instrument with its high spectral resolution in a wide range of applications. The spectral reduction technique is the core of the data processing of the echelle spectrometer, which realizes the rapid reduction of two-dimensional images to one-dimensional spectra by establishing the correspondence between wavelength and imaging position. The performance of the echelle spectrometer is directly determined by the accuracy of spectral reduction, which is the most important point and greatest difficulty in instrument development. In view of this, the development of the spectral reduction technique is reviewed, and its evolution is classified into three stages: ray tracing, modeling, and calibration methods. The core ideas and principles of spectral reduction algorithms in each stage are discussed in detail. Finally, the development history is summarized, the development trend is predicted, and the outlook of the development direction for the echelle spectrometer spectral reduction technology is discussed.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2024
- Vol. 61, Issue 3, 0330003 (2024)
Detection of Hydrogen Sulfide Gas in Sewer Based on Light-Induced Thermoelastic Spectroscopy (Invited)
Meijing Zhou, Xiaoli Liu, Ruyue Cui, Jiyu Xue, Lei Dong, and Hongpeng Wu
Light-induced thermoelastic spectroscopy (LITES) technology is a novel trace gas detection technology that has developed rapidly in recent years. The technology employs miniature, cost-effective, and wavelength-insensitive quartz tuning fork as substitutes for high-cost, narrow-bandwidth photodetectors in the field of optoelectronic transduction. The target gas concentration is achieved by detecting the variation in optical intensity resulting from the interaction between laser radiation and the target gas. LITES technology has the advantages of high detection sensitivity, short response time, and independence of excitation wavelength. In this paper, the research of trace gas detection system based on LITES technology is carried out with hydrogen sulfide (H2S) gas in sewers as the measurement target. A near-infrared distributed feedback laser with an output wavelength of 1.582 μm is employed as the excitation light source. The wavelength modulation spectroscopy and second harmonic detection techniques are utilized for trace gas concentration measurements. The impact of laser wavelength modulation depth on the signal amplitude generated by the LITES system is analyzed, and then the effect of operating pressure on the performance of the LITES system is also studied in detail. In addition, to further improve the detection sensitivity of the device, a Herriott multipass cell with an effective optical path length of 14.5 m is assembled between the laser and the quartz tuning fork. The sensor reached a minimum detection limit of ~4.87×10-7 of H2S with an integration time of 300 ms. By extending the integration time to 52 s, the minimum limit can be reduced to ~7.78×10-8. Using optimized parameters, on-site measurements of H2S in the sewer are conducted. The results indicate that the system is fully capable of meeting the application requirements in the fields of sewer odor monitoring and analysis. Light-induced thermoelastic spectroscopy (LITES) technology is a novel trace gas detection technology that has developed rapidly in recent years. The technology employs miniature, cost-effective, and wavelength-insensitive quartz tuning fork as substitutes for high-cost, narrow-bandwidth photodetectors in the field of optoelectronic transduction. The target gas concentration is achieved by detecting the variation in optical intensity resulting from the interaction between laser radiation and the target gas. LITES technology has the advantages of high detection sensitivity, short response time, and independence of excitation wavelength. In this paper, the research of trace gas detection system based on LITES technology is carried out with hydrogen sulfide (H2S) gas in sewers as the measurement target. A near-infrared distributed feedback laser with an output wavelength of 1.582 μm is employed as the excitation light source. The wavelength modulation spectroscopy and second harmonic detection techniques are utilized for trace gas concentration measurements. The impact of laser wavelength modulation depth on the signal amplitude generated by the LITES system is analyzed, and then the effect of operating pressure on the performance of the LITES system is also studied in detail. In addition, to further improve the detection sensitivity of the device, a Herriott multipass cell with an effective optical path length of 14.5 m is assembled between the laser and the quartz tuning fork. The sensor reached a minimum detection limit of ~4.87×10-7 of H2S with an integration time of 300 ms. By extending the integration time to 52 s, the minimum limit can be reduced to ~7.78×10-8. Using optimized parameters, on-site measurements of H2S in the sewer are conducted. The results indicate that the system is fully capable of meeting the application requirements in the fields of sewer odor monitoring and analysis.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2024
- Vol. 61, Issue 3, 0330002 (2024)
Research Progress of Infrared Spectroscopy Technology Enhanced by Polaritons in Two-Dimensional Materials (Invited)
Wei Wei, Guilian Lan, Peng Luo, and Linlong Tang
Surface-enhanced infrared absorption spectroscopy technology substantially boosts the interaction between light and molecules by confining the infrared light around the detection molecules, enabling susceptible detection of weak molecular vibration signals. Recent advancements in polariton in two-dimensional materials offer an effective strategy for enhancing surface-enhanced infrared spectroscopy because of their unique properties, such as highly confined electric field and low intrinsic loss. This study reviews the ongoing research progress of infrared spectroscopy technology enhanced by polaritons in two-dimensional materials. We begin by outlining the fundamental characteristics of polaritons in various materials and discussing the coupling mechanisms between polaritons and molecular modes. Building on this, we summarize the key research interests in polariton-enhanced infrared spectroscopy technology, including plasmon-enhanced, phonon polariton-enhanced, and near-field enhancement infrared spectroscopy technology. In conclusion, we provide a prospective outlook on the future development directions of polariton-enhanced infrared spectroscopy technology. Surface-enhanced infrared absorption spectroscopy technology substantially boosts the interaction between light and molecules by confining the infrared light around the detection molecules, enabling susceptible detection of weak molecular vibration signals. Recent advancements in polariton in two-dimensional materials offer an effective strategy for enhancing surface-enhanced infrared spectroscopy because of their unique properties, such as highly confined electric field and low intrinsic loss. This study reviews the ongoing research progress of infrared spectroscopy technology enhanced by polaritons in two-dimensional materials. We begin by outlining the fundamental characteristics of polaritons in various materials and discussing the coupling mechanisms between polaritons and molecular modes. Building on this, we summarize the key research interests in polariton-enhanced infrared spectroscopy technology, including plasmon-enhanced, phonon polariton-enhanced, and near-field enhancement infrared spectroscopy technology. In conclusion, we provide a prospective outlook on the future development directions of polariton-enhanced infrared spectroscopy technology.
Laser & Optoelectronics Progress
- Publication Date: Feb. 10, 2024
- Vol. 61, Issue 3, 0330001 (2024)
Ultrafast Two-Dimensional Electronic Spectroscopy (Invited)
Changtao Xiao, Yin Song, and Weiqian Zhao
Since the past two decades, ultrafast two-dimensional electronic spectroscopy (2DES) has made remarkable progress, and it plays a pivotal tool in unraveling population and coherent dynamics in photosynthesis, photovoltaic, and low-dimensional materials. This review presents a comprehensive overview of the progress in 2DES, with a focus on its ability to expand spectral windows and dimensions. Furthermore, it examines the current challenges and future directions of this field. From a technical perspective, a key bottleneck preventing the wide application of 2DES is the need to overcome experimental hurdles and develop sophisticated multispectral data analysis methods. In cutting-edge research, a crucial question centers on the development of novel 2DES techniques to effectively probe and disentangle various processes within coherent dynamics and polaritonic systems. Since the past two decades, ultrafast two-dimensional electronic spectroscopy (2DES) has made remarkable progress, and it plays a pivotal tool in unraveling population and coherent dynamics in photosynthesis, photovoltaic, and low-dimensional materials. This review presents a comprehensive overview of the progress in 2DES, with a focus on its ability to expand spectral windows and dimensions. Furthermore, it examines the current challenges and future directions of this field. From a technical perspective, a key bottleneck preventing the wide application of 2DES is the need to overcome experimental hurdles and develop sophisticated multispectral data analysis methods. In cutting-edge research, a crucial question centers on the development of novel 2DES techniques to effectively probe and disentangle various processes within coherent dynamics and polaritonic systems.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2024
- Vol. 61, Issue 1, 0130002 (2024)
Dispersion Rate of Single-Stage Virtually Imaged Phased Array Spectrometer for Two-Dimensional Imaging of the Cornea and Lens (Invited)
Xingdao He, Jin Xu, Mingxuan Liu, and Jiulin Shi
Owing to its simple structure and high light output, Brillouin scattering detection technology based on single-stage virtually imaged phase array (VIPA) spectroscopy has enabled the rapid detection of transparent biological tissue elasticity. The cornea and lens are typical transparent biological tissues. However, elastic scattering can easily overwhelm the weak Brillouin signal in a single-stage VIPA spectrometer, thereby limiting the signal-to-noise ratio and resolution enhancement. This problem has hindered further clinical applications of single-stage VIPA technology. Therefore, this paper investigated theoretical and experimental methods for improving the performance of single-stage VIPA spectroscopy. Theoretically, a paraxial approximate dispersion model of the VIPA was constructed to investigate the variations in the dispersion ratio with the collimated beam radius in front of the cylindrical lens, the focal lengths of the cylindrical and spherical lenses, and the tilt angle of the VIPA. The dispersion rate was primarily affected by the focal length of the spherical lens, the VIPA tilt angle, and the detector resolution. Experimentally, a signal-receiving device combining a zoom lens and high-resolution complementary metal-oxide semiconductor camera was designed and matched to the system. This device balances the dispersion rate and scattering signal intensity, optimizes the parameters of the spectrometer system, and improves the system performance. This paper originally reports the two-dimensional frequency-shift imaging of ex-vivo porcine cornea and lens using a single-stage VIPA spectrometer. The results of this study are expected to advance the field of clinical diagnosis and treatment using single-stage VIPA spectroscopy. Owing to its simple structure and high light output, Brillouin scattering detection technology based on single-stage virtually imaged phase array (VIPA) spectroscopy has enabled the rapid detection of transparent biological tissue elasticity. The cornea and lens are typical transparent biological tissues. However, elastic scattering can easily overwhelm the weak Brillouin signal in a single-stage VIPA spectrometer, thereby limiting the signal-to-noise ratio and resolution enhancement. This problem has hindered further clinical applications of single-stage VIPA technology. Therefore, this paper investigated theoretical and experimental methods for improving the performance of single-stage VIPA spectroscopy. Theoretically, a paraxial approximate dispersion model of the VIPA was constructed to investigate the variations in the dispersion ratio with the collimated beam radius in front of the cylindrical lens, the focal lengths of the cylindrical and spherical lenses, and the tilt angle of the VIPA. The dispersion rate was primarily affected by the focal length of the spherical lens, the VIPA tilt angle, and the detector resolution. Experimentally, a signal-receiving device combining a zoom lens and high-resolution complementary metal-oxide semiconductor camera was designed and matched to the system. This device balances the dispersion rate and scattering signal intensity, optimizes the parameters of the spectrometer system, and improves the system performance. This paper originally reports the two-dimensional frequency-shift imaging of ex-vivo porcine cornea and lens using a single-stage VIPA spectrometer. The results of this study are expected to advance the field of clinical diagnosis and treatment using single-stage VIPA spectroscopy.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2024
- Vol. 61, Issue 1, 0130001 (2024)
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