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Spectroscopy|77 Article(s)
Highly sensitive carbon dioxide detection based on enhanced photoacoustic spectroscopy with a thulium-doped fiber amplifier
Fupeng Wang, Ze Han, Jianguo Zhang, Jinghua Wu, and Qiang Wang
A thulium-doped fiber amplifier-enhanced photoacoustic spectroscopy (TDFE-PAS) sensor was developed for carbon dioxide (CO2) detection utilizing a 2004 nm distributed feedback (DFB) laser. The thulium-doped fiber was in-band pumped by a 1567 nm source to amplify the optical power of 2004 nm to enhance the photoacoustic excitation. As a result, the photoacoustic signal was enhanced over 101 times. Based on a 7.9 mL differential PA cell, the sensor achieved a linearity of R2 = 0.9997 on CO2 detection in a wide concentration range of 0–10,000 ppm (part per million). The noise equivalent detection limit was evaluated to be 190 ppb (part per billion) at a response time of 10 s. A thulium-doped fiber amplifier-enhanced photoacoustic spectroscopy (TDFE-PAS) sensor was developed for carbon dioxide (CO2) detection utilizing a 2004 nm distributed feedback (DFB) laser. The thulium-doped fiber was in-band pumped by a 1567 nm source to amplify the optical power of 2004 nm to enhance the photoacoustic excitation. As a result, the photoacoustic signal was enhanced over 101 times. Based on a 7.9 mL differential PA cell, the sensor achieved a linearity of R2 = 0.9997 on CO2 detection in a wide concentration range of 0–10,000 ppm (part per million). The noise equivalent detection limit was evaluated to be 190 ppb (part per billion) at a response time of 10 s.
Chinese Optics Letters
- Publication Date: Mar. 10, 2025
- Vol. 23, Issue 2, 023001 (2025)
Highly sensitive CO2-LITES sensor based on a self-designed low-frequency quartz tuning fork and fiber-coupled MPC
Jinfeng Hou, Xiaonan Liu, Yahui Liu, Ying He, Weijiang Zhao, and Yufei Ma
A highly sensitive carbon dioxide (CO2) sensor based on light-induced thermoelastic spectroscopy (LITES) utilizing a self-designed low-frequency quartz tuning fork (QTF) and a fiber-coupled multipass cell (MPC) is reported in this paper. The QTF with a low resonant frequency of 8675 Hz and a high Q factor of 11,675.64 was used to improve its energy accumulation time and the sensor’s signal level. The MPC with the fiber-coupled structure and optical length of 40 m was adopted to significantly increase the gas absorbance and reduce the optical alignment difficulty as well as improve the robustness of the sensor system. A distributed feedback (DFB), near-infrared diode laser with an emission wavelength of 1.57 µm was used as an excitation source. The experimental results showed that this CO2-LITES sensor had an excellent linear response to CO2 concentrations. The minimum detection limitation (MDL) of this CO2-LITES sensor was obtained to be 445.91 ppm, and it could be improved to 47.70 ppm (parts per million) when the integration time of the system reached 500 s. Further improvement methods for the detection performance of such sensors were also discussed. A highly sensitive carbon dioxide (CO2) sensor based on light-induced thermoelastic spectroscopy (LITES) utilizing a self-designed low-frequency quartz tuning fork (QTF) and a fiber-coupled multipass cell (MPC) is reported in this paper. The QTF with a low resonant frequency of 8675 Hz and a high Q factor of 11,675.64 was used to improve its energy accumulation time and the sensor’s signal level. The MPC with the fiber-coupled structure and optical length of 40 m was adopted to significantly increase the gas absorbance and reduce the optical alignment difficulty as well as improve the robustness of the sensor system. A distributed feedback (DFB), near-infrared diode laser with an emission wavelength of 1.57 µm was used as an excitation source. The experimental results showed that this CO2-LITES sensor had an excellent linear response to CO2 concentrations. The minimum detection limitation (MDL) of this CO2-LITES sensor was obtained to be 445.91 ppm, and it could be improved to 47.70 ppm (parts per million) when the integration time of the system reached 500 s. Further improvement methods for the detection performance of such sensors were also discussed.
Chinese Optics Letters
- Publication Date: Jul. 30, 2024
- Vol. 22, Issue 7, 073001 (2024)
All-fiber high-resolution computational spectropolarimeter based on speckle pattern
Qianyu Zhou, Yangyang Wan, Xinyu Fan, and Zuyuan He
The lightwave field possesses several dimensional properties, including amplitude, spectrum, phase, and polarization. Multi-dimensional measurements of lightwaves have diverse applications ranging from remote sensing to analytical chemistry. However, achieving high-resolution simultaneous multi-dimensional measurement of lightwaves remains challenging. In this work, we demonstrate an all-fiber spectropolarimeter based on a speckle pattern obtained from the end of a multi-mode fiber. The proposed system simultaneously achieves a spectral resolution of 100 pm and a polarization resolution of 0.001437. The polarization measurement errors for three Stokes parameters are 3.37%, 1.01%, and 0.84%, respectively, with a mean squared error of 5.3 × 10-5. This work provides novel potential for high-resolution and accurate multi-dimensional lightwave field measurements. The lightwave field possesses several dimensional properties, including amplitude, spectrum, phase, and polarization. Multi-dimensional measurements of lightwaves have diverse applications ranging from remote sensing to analytical chemistry. However, achieving high-resolution simultaneous multi-dimensional measurement of lightwaves remains challenging. In this work, we demonstrate an all-fiber spectropolarimeter based on a speckle pattern obtained from the end of a multi-mode fiber. The proposed system simultaneously achieves a spectral resolution of 100 pm and a polarization resolution of 0.001437. The polarization measurement errors for three Stokes parameters are 3.37%, 1.01%, and 0.84%, respectively, with a mean squared error of 5.3 × 10-5. This work provides novel potential for high-resolution and accurate multi-dimensional lightwave field measurements.
Chinese Optics Letters
- Publication Date: Dec. 24, 2024
- Vol. 22, Issue 12, 123001 (2024)
Multiple wavelength frequency stabilization with a single transfer cavity for mercury optical lattice clock
Li Ma, Qixin Liu, Haiyang Song, Jianfang Sun, and Zhen Xu
A simple and robust multiple wavelength frequency stabilization system is demonstrated using a single transfer cavity and a 1062-nm ultra-stable laser for all the lasers used in a mercury optical lattice clock. Offset sideband locking is employed to tune the laser frequency while dichroic mirrors and differentiated modulation frequencies are utilized for the Pound–Drever–Hall locking of four-color lasers. For the most demanding lasers at 1015 nm and 725 nm, the line width of the beat note is reduced to 27 kHz and 17 kHz, respectively. The frequency fluctuation for the transfer-locked 1015-nm laser is less than 10 kHz, which is much better than the lasers locked to an atomic spectrum. Using its high stability of 5 × 10-12 over 100 s, the transfer-locked 1015-nm laser is employed for low-noise frequency modulated saturated absorption spectroscopy. This approach could also be used in various situations for the research of optical clocks, Rydberg atoms, laser cooling of molecules, and quantum computation with neutral atoms. A simple and robust multiple wavelength frequency stabilization system is demonstrated using a single transfer cavity and a 1062-nm ultra-stable laser for all the lasers used in a mercury optical lattice clock. Offset sideband locking is employed to tune the laser frequency while dichroic mirrors and differentiated modulation frequencies are utilized for the Pound–Drever–Hall locking of four-color lasers. For the most demanding lasers at 1015 nm and 725 nm, the line width of the beat note is reduced to 27 kHz and 17 kHz, respectively. The frequency fluctuation for the transfer-locked 1015-nm laser is less than 10 kHz, which is much better than the lasers locked to an atomic spectrum. Using its high stability of 5 × 10-12 over 100 s, the transfer-locked 1015-nm laser is employed for low-noise frequency modulated saturated absorption spectroscopy. This approach could also be used in various situations for the research of optical clocks, Rydberg atoms, laser cooling of molecules, and quantum computation with neutral atoms.
Chinese Optics Letters
- Publication Date: Oct. 14, 2024
- Vol. 22, Issue 10, 103001 (2024)
Terahertz spectroscopy of water in nonionic reverse micelles
Jiaqi Zhang, Yuyue Yan, Liyuan Liu, and Weili Zhang
The dynamics of water within a nanopool of a reverse micelle is heavily affected by the amphiphilic interface. In this work, the terahertz (THz) spectra of cyclohexane/Igepal/water nonionic reverse micelle mixture are measured by THz time-domain spectroscopy and analyzed with two Debye models and complex permittivity of background with volume ratios. Based on the fitted parameters of bulk and fast water, the molar concentration of all kinds of water molecules and hydration water molecule number per Igepal molecule are calculated. We find that slow hydration water has the highest proportion in water when the radius parameter ω0<10, while bulk water becomes the main component when ω0≥10. The feature radius ratio of nonhydrated and hydrated water to total water nanopool is roughly obtained from 0.39 to 0.85 with increasing ω0. The dynamics of water within a nanopool of a reverse micelle is heavily affected by the amphiphilic interface. In this work, the terahertz (THz) spectra of cyclohexane/Igepal/water nonionic reverse micelle mixture are measured by THz time-domain spectroscopy and analyzed with two Debye models and complex permittivity of background with volume ratios. Based on the fitted parameters of bulk and fast water, the molar concentration of all kinds of water molecules and hydration water molecule number per Igepal molecule are calculated. We find that slow hydration water has the highest proportion in water when the radius parameter ω0<10, while bulk water becomes the main component when ω0≥10. The feature radius ratio of nonhydrated and hydrated water to total water nanopool is roughly obtained from 0.39 to 0.85 with increasing ω0.
Chinese Optics Letters
- Publication Date: Jan. 08, 2024
- Vol. 22, Issue 1, 013001 (2024)
Rapid classification of copper concentrate by portable laser-induced breakdown spectroscopy combined with transfer learning and deep convolutional neural network
Haochen Li, Tianyuan Liu, Yuchao Fu, Wanxiang Li, Meng Zhang, Xi Yang, Di Song, Jiaqi Wang, You Wang, and Meizhen Huang
This paper investigates the combination of laser-induced breakdown spectroscopy (LIBS) and deep convolutional neural networks (CNNs) to classify copper concentrate samples using pretrained CNN models through transfer learning. Four pretrained CNN models were compared. The LIBS profiles were augmented into 2D matrices. Three transfer learning methods were tried. All the models got a high classification accuracy of >92%, with the highest at 96.2% for VGG16. These results suggested that the knowledge learned from machine vision by the CNN models can accelerate the training process and reduce the risk of overfitting. The results showed that deep CNN and transfer learning have great potential for the classification of copper concentrates by portable LIBS. This paper investigates the combination of laser-induced breakdown spectroscopy (LIBS) and deep convolutional neural networks (CNNs) to classify copper concentrate samples using pretrained CNN models through transfer learning. Four pretrained CNN models were compared. The LIBS profiles were augmented into 2D matrices. Three transfer learning methods were tried. All the models got a high classification accuracy of >92%, with the highest at 96.2% for VGG16. These results suggested that the knowledge learned from machine vision by the CNN models can accelerate the training process and reduce the risk of overfitting. The results showed that deep CNN and transfer learning have great potential for the classification of copper concentrates by portable LIBS.
Chinese Optics Letters
- Publication Date: Apr. 06, 2023
- Vol. 21, Issue 4, 043001 (2023)
Advances in multipass cell for absorption spectroscopy-based trace gas sensing technology [Invited]
Yahui Liu, and Yufei Ma
In the field of absorption spectroscopy, the multipass cell (MPC) is one of the key elements. It has the advantages of simple structure, easy adjustment, and high spectral coverage, which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy. This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years, and briefly introduces the application of some processed products. The design theory of modified ABCD matrix and vector reflection principle are explained in detail. Finally, trends in its development are predicted. In the field of absorption spectroscopy, the multipass cell (MPC) is one of the key elements. It has the advantages of simple structure, easy adjustment, and high spectral coverage, which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy. This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years, and briefly introduces the application of some processed products. The design theory of modified ABCD matrix and vector reflection principle are explained in detail. Finally, trends in its development are predicted.
Chinese Optics Letters
- Publication Date: Dec. 01, 2022
- Vol. 21, Issue 3, 033001 (2023)
Optical emission spectrometric diagnosis of laser-induced plasma and shock front produced at moderate pressure
Xin Peng, Minsun Chen, and Hao Liu
We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa. The significant shock front and spatial fractionation among the different charged ions are demonstrated at the pressure of 20 Pa. The collisions between Si IV ions and ambient Ar atoms generate distinct and excited Ar II ions, fresh Si III ions, and electrons at the dense layer. The electron density peaks at the position of the shock front, indicating that the collision that yields electrons is dominant over the recombination process in the region of the shock layer and its immediate vicinity. We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa. The significant shock front and spatial fractionation among the different charged ions are demonstrated at the pressure of 20 Pa. The collisions between Si IV ions and ambient Ar atoms generate distinct and excited Ar II ions, fresh Si III ions, and electrons at the dense layer. The electron density peaks at the position of the shock front, indicating that the collision that yields electrons is dominant over the recombination process in the region of the shock layer and its immediate vicinity.
Chinese Optics Letters
- Publication Date: Oct. 13, 2022
- Vol. 21, Issue 2, 023001 (2023)
Improvement of Raman spectrum uniformity of SERS substrate based on flat electrode
Zhihui Jiang, Shen Zhang, Congxi Song, Hongmin Mao, Xin Zhao, Huanjun Lu, and Zhaoliang Cao
The distribution of metal nanoparticles on the surface of a surface enhancement Raman scattering (SERS)-active substrate plays a prominent part in not only the enhancement of Raman vibration signal, but also the spectrum uniformity. Here, a facile method to fabricate SERS substrates with excellent homogeneity and low cost was proposed, in which a lyotropic liquid crystal soft template was introduced for the coordinated growth of the silver nanoflowers in the process of electrochemistry deposition. Simulation was carried out to illustrate the dominated influence of the distance of electrodes on the deposited nanoparticle number. Two kinds of conductive materials, silver plate and indium tin oxide (ITO) glass, were chosen as the anode, while the cathode was fixed as ITO glass. The simulated conjecture on the effect of electrode flatness on the uniformity of deposited nanoparticles in silver is experimentally proved. More importantly, it was demonstrated that with a relatively smooth and flat ITO glass anode, a SERS substrate featuring higher spectrum uniformity could be achieved. This work is of great significance to the actual applications of the SERS substrate for quantitative detection with high sensitivity. The distribution of metal nanoparticles on the surface of a surface enhancement Raman scattering (SERS)-active substrate plays a prominent part in not only the enhancement of Raman vibration signal, but also the spectrum uniformity. Here, a facile method to fabricate SERS substrates with excellent homogeneity and low cost was proposed, in which a lyotropic liquid crystal soft template was introduced for the coordinated growth of the silver nanoflowers in the process of electrochemistry deposition. Simulation was carried out to illustrate the dominated influence of the distance of electrodes on the deposited nanoparticle number. Two kinds of conductive materials, silver plate and indium tin oxide (ITO) glass, were chosen as the anode, while the cathode was fixed as ITO glass. The simulated conjecture on the effect of electrode flatness on the uniformity of deposited nanoparticles in silver is experimentally proved. More importantly, it was demonstrated that with a relatively smooth and flat ITO glass anode, a SERS substrate featuring higher spectrum uniformity could be achieved. This work is of great significance to the actual applications of the SERS substrate for quantitative detection with high sensitivity.
Chinese Optics Letters
- Publication Date: Nov. 01, 2023
- Vol. 21, Issue 11, 113001 (2023)
Reconstruction and fitting of second-harmonic signals by wavelength modulation spectroscopy method based on fast Fourier transform
Linquan Lai, Yue Chen, Kongtao Chen, Jiale Tang, Kaiwen Yin, Fuqiang Jia, Dun Qiao, Yuanlong Fan, Kang Li, and Nigel Copner
Conventional wavelength modulation spectroscopy (WMS) is vulnerable to the influence of low-frequency noise. Accuracy of the method highly depends on the performance of the costly lock-in amplifier. In this article, we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform (FFT). This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave. Formulation and detection procedures were presented. The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method. Second-harmonic waveforms acquired by the two means are generally consistent. The experimental study validates the obtained gas concentration from 5% to 30%, showing a good linear relationship by the proposed method. The maximum relative error on concentration extraction is 2.87%; as for conventional WMS, this value is 4.50%. The developed measurement method may have potential in computed tomography. Conventional wavelength modulation spectroscopy (WMS) is vulnerable to the influence of low-frequency noise. Accuracy of the method highly depends on the performance of the costly lock-in amplifier. In this article, we report a new and effective method for reconstructing second-harmonic signals through WMS based on fast Fourier transform (FFT). This method is less disturbed by low-frequency noise because it does not use a low-frequency ramp wave. Formulation and detection procedures were presented. The discrete second-harmonic waveform can be obtained by continuously changing the DC signal and FFT analysis in this method. Second-harmonic waveforms acquired by the two means are generally consistent. The experimental study validates the obtained gas concentration from 5% to 30%, showing a good linear relationship by the proposed method. The maximum relative error on concentration extraction is 2.87%; as for conventional WMS, this value is 4.50%. The developed measurement method may have potential in computed tomography.
Chinese Optics Letters
- Publication Date: Jun. 15, 2022
- Vol. 20, Issue 9, 093001 (2022)
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