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Spectroscopy
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73 Article(s)
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.
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Chinese Optics Letters
Publication Date: Jan. 08, 2024
Vol. 22, Issue 1, 013001 (2024)
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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.
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Chinese Optics Letters
Publication Date: Apr. 06, 2023
Vol. 21, Issue 4, 043001 (2023)
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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.
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Chinese Optics Letters
Publication Date: Dec. 01, 2022
Vol. 21, Issue 3, 033001 (2023)
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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.
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Chinese Optics Letters
Publication Date: Oct. 13, 2022
Vol. 21, Issue 2, 023001 (2023)
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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.
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Chinese Optics Letters
Publication Date: Nov. 01, 2023
Vol. 21, Issue 11, 113001 (2023)
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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.
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Chinese Optics Letters
Publication Date: Jun. 15, 2022
Vol. 20, Issue 9, 093001 (2022)
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Optical analysis method for fast plasma characterization of high-speed miniaturized synthetic jet
Ye Yuan, Yan Zhang, Cheng Guo, Xiaolu Kang, Zhong Yan, Xiaoping Huang, and Qing Zhao
In this paper, a new optical analysis method for plasma characterization is proposed. Plasma characteristics are obtained directly by measuring the plasma luminous color, rather than the complex spectral diagnosis method, which is difficult to obtain at high speed. By using the light transmittance curve of the human cornea, the RGB coordinates are calculated from the measured plasma spectrum data. Plasma characteristics are diagnosed using the Boltzmann plot method and the Stark broadening method. The corresponding relationship of the electron temperature, electron density data points, and luminous color is established and analyzed. Our research results indicate that this optical analysis method is feasible and promising for fast plasma characterization.
In this paper, a new optical analysis method for plasma characterization is proposed. Plasma characteristics are obtained directly by measuring the plasma luminous color, rather than the complex spectral diagnosis method, which is difficult to obtain at high speed. By using the light transmittance curve of the human cornea, the RGB coordinates are calculated from the measured plasma spectrum data. Plasma characteristics are diagnosed using the Boltzmann plot method and the Stark broadening method. The corresponding relationship of the electron temperature, electron density data points, and luminous color is established and analyzed. Our research results indicate that this optical analysis method is feasible and promising for fast plasma characterization.
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Chinese Optics Letters
Publication Date: May. 04, 2022
Vol. 20, Issue 7, 073001 (2022)
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Extraction of optical constants in the terahertz band using material dispersion models
Jian Gu, Jiaojiao Ren, Dandan Zhang, and Lijuan Li
This study proposes a method based on material dispersion models to computationally simulate terahertz (THz) time-domain spectroscopy signals. The proposed method can accurately extract the refractive indices and extinction coefficients of optically thin samples and high-absorption materials in the THz band. This method was successfully used to extract the optical constants of a 470-μm-thick monocrystalline silicon sample and eliminate all errors associated with the Fabry–Pérot oscillation. When used to extract the optical constants of a 16.29-mm-thick polycarbonate sample, our method succeeded in minimizing errors caused by the low signal-to-noise ratio in the extracted optical constants.
This study proposes a method based on material dispersion models to computationally simulate terahertz (THz) time-domain spectroscopy signals. The proposed method can accurately extract the refractive indices and extinction coefficients of optically thin samples and high-absorption materials in the THz band. This method was successfully used to extract the optical constants of a 470-μm-thick monocrystalline silicon sample and eliminate all errors associated with the Fabry–Pérot oscillation. When used to extract the optical constants of a 16.29-mm-thick polycarbonate sample, our method succeeded in minimizing errors caused by the low signal-to-noise ratio in the extracted optical constants.
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Chinese Optics Letters
Publication Date: Mar. 30, 2022
Vol. 20, Issue 5, 053001 (2022)
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VIPA-based two-component detection for a coherent population trapping experiment
Aihua Deng, Zixuan Zeng, and Jianliao Deng
We demonstrate a two-component detection of a coherent population trapping (CPT) resonance based on virtually imaged phased array (VIPA). After passing through a VIPA, the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually. The asymmetric lineshape is observed experimentally in the CPT signal for each component, and the comparison with the conventional detection is presented. The shift of the CPT resonant frequency is studied with both the two-component and one-component detections. Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.
We demonstrate a two-component detection of a coherent population trapping (CPT) resonance based on virtually imaged phased array (VIPA). After passing through a VIPA, the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually. The asymmetric lineshape is observed experimentally in the CPT signal for each component, and the comparison with the conventional detection is presented. The shift of the CPT resonant frequency is studied with both the two-component and one-component detections. Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.
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Chinese Optics Letters
Publication Date: Aug. 10, 2021
Vol. 19, Issue 8, 083001 (2021)
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Influence of a dielectric decoupling layer on the local electric field and molecular spectroscopy in plasmonic nanocavities: a numerical study
Gong Chen, Jiazhe Zhu, and Xiaoguang Li
In this Letter, we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction. It is found that both the intensity and spatial confinement of the electric field and molecular spectroscopy can be significantly enhanced by applying a dielectric layer with large dielectric constant. We also discuss the optimal dielectric layer thickness to obtain the largest quantum efficiency of a dipole emitter. These results may be instructive for further studies in molecular spectroscopy and optoelectronics in plasmonic junctions.
In this Letter, we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction. It is found that both the intensity and spatial confinement of the electric field and molecular spectroscopy can be significantly enhanced by applying a dielectric layer with large dielectric constant. We also discuss the optimal dielectric layer thickness to obtain the largest quantum efficiency of a dipole emitter. These results may be instructive for further studies in molecular spectroscopy and optoelectronics in plasmonic junctions.
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Chinese Optics Letters
Publication Date: Dec. 10, 2021
Vol. 19, Issue 12, 123001 (2021)
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