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Spectroscopy|21 Article(s)
Blind spectral deconvolution algorithm for Raman spectrum with Poisson noise
Hai Liu, Zhaoli Zhang, Jianwen Sun, and and Sanya Liu
A blind deconvolution algorithm with modified Tikhonov regularization is introduced. To improve the spectral resolution, spectral structure information is incorporated into regularization by using the adaptive term to distinguish the spectral structure from other regions. The proposed algorithm can effectively suppress Poisson noise as well as preserve the spectral structure and detailed information. Moreover, it becomes more robust with the change of the regularization parameter. Comparative results on simulated and real degraded Raman spectra are reported. The recovered Raman spectra can easily extract the spectral features and interpret the unknown chemical mixture. A blind deconvolution algorithm with modified Tikhonov regularization is introduced. To improve the spectral resolution, spectral structure information is incorporated into regularization by using the adaptive term to distinguish the spectral structure from other regions. The proposed algorithm can effectively suppress Poisson noise as well as preserve the spectral structure and detailed information. Moreover, it becomes more robust with the change of the regularization parameter. Comparative results on simulated and real degraded Raman spectra are reported. The recovered Raman spectra can easily extract the spectral features and interpret the unknown chemical mixture.
Photonics Research
- Publication Date: Nov. 15, 2014
- Vol. 2, Issue 6, 06000168 (2014)
Tip-enhanced photoluminescence spectroscopy of monolayer MoS2
Lingyan Meng, and Mengtao Sun
Probing the optical properties of molybdenum disulfide (MoS2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the Raman and fluorescence properties of monolayer MoS2 using tip-enhanced spectroscopy (TES). In the strong-coupling TES system, the Raman and fluorescence enhancement factors can be turned to as high as 4.5×108 and 3.3×103, respectively, by optimizing the tip–MoS2-film distance. Our theoretical results not only help to deeply understand the TES properties of monolayer MoS2, but also provide better guidance on the applications of the novel two-dimensional material. Probing the optical properties of molybdenum disulfide (MoS2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the Raman and fluorescence properties of monolayer MoS2 using tip-enhanced spectroscopy (TES). In the strong-coupling TES system, the Raman and fluorescence enhancement factors can be turned to as high as 4.5×108 and 3.3×103, respectively, by optimizing the tip–MoS2-film distance. Our theoretical results not only help to deeply understand the TES properties of monolayer MoS2, but also provide better guidance on the applications of the novel two-dimensional material.
Photonics Research
- Publication Date: Oct. 31, 2017
- Vol. 5, Issue 6, 06000745 (2017)
Robust and accurate terahertz time-domain spectroscopic ellipsometry
Xuequan Chen, Edward P. J. Parrott, Zhe Huang, Hau-Ping Chan, and Emma Pickwell-MacPherson
In this work, we show how fiber-based terahertz systems can be robustly configured for accurate terahertz ellipsometry. To this end, we explain how our algorithms can be successfully applied to achieve accurate spectroscopic ellipsometry with a high tolerance on the imperfect polarizer extinction ratio and pulse shift errors. Highly accurate characterization of transparent, absorptive, and conductive samples comprehensively demonstrates the versatility of our algorithms. The improved accuracy we achieve is a fundamental breakthrough for reflection-based measurements and overcomes the hurdle of phase uncertainty. In this work, we show how fiber-based terahertz systems can be robustly configured for accurate terahertz ellipsometry. To this end, we explain how our algorithms can be successfully applied to achieve accurate spectroscopic ellipsometry with a high tolerance on the imperfect polarizer extinction ratio and pulse shift errors. Highly accurate characterization of transparent, absorptive, and conductive samples comprehensively demonstrates the versatility of our algorithms. The improved accuracy we achieve is a fundamental breakthrough for reflection-based measurements and overcomes the hurdle of phase uncertainty.
Photonics Research
- Publication Date: Jul. 05, 2018
- Vol. 6, Issue 8, 08000768 (2018)
X-ray absorption spectroscopy study of energy transport in foil targets heated by petawatt laser pulses
I. Y. Skobelev, S. N. Ryazantsev, D. D. Arich, P. S. Bratchenko, A. Y. Faenov, T. A. Pikuz, P. Durey, L. Doehl, D. Farley, C. D. Baird, K. L. Lancaster, C. D. Murphy, N. Booth, C. Spindloe, P. McKenna, S. B. Hansen, J. Colgan, R. Kodama, N. Woolsey, and S. A. Pikuz
X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5×1020 and 2.5×1020 W/cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity. X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5×1020 and 2.5×1020 W/cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.
Photonics Research
- Publication Date: Mar. 02, 2018
- Vol. 6, Issue 4, 04000234 (2018)
Raman spectroscopy regulation in van der Waals crystals
Wei Zheng, Yanming Zhu, Fadi Li, and Feng Huang
Raman spectroscopy is a versatile tool widely used for comprehensive probing of crystal information. However, generally when applied in narrow-band-gap van der Waals crystals, it is liable to form a “bug,” especially in transition-metal-dichalcogenides (TMDs). That is, several resonant Raman-scattering (RS) modes will inevitably appear in the Raman spectra with strong intensity, interfering with the desired signal of optical-phonon modes. Here, we propose cross-sectional polarized Raman scattering capable of regulating the intensity of RS modes in accordance with quasi-sinusoidal rules. Typically, for MoS2 and WS2, when the polarization vector of excited light is along the c axis of the crystal, all RS modes are nearly completely “expunged” from the Raman spectra. The mechanism is that the absorption of most TMDs with a space group of R3m for the light polarized along the c axis is infinitesimal, thus forming a small coupling intensity of electronic states excited optically and acoustic-phonon modes at point M, which in turn restrain the appearance of RS modes. The regulating strategy proposed can be applied to other van der Waals crystals so as to obtain a high signal-to-noise ratio Raman spectrum. Raman spectroscopy is a versatile tool widely used for comprehensive probing of crystal information. However, generally when applied in narrow-band-gap van der Waals crystals, it is liable to form a “bug,” especially in transition-metal-dichalcogenides (TMDs). That is, several resonant Raman-scattering (RS) modes will inevitably appear in the Raman spectra with strong intensity, interfering with the desired signal of optical-phonon modes. Here, we propose cross-sectional polarized Raman scattering capable of regulating the intensity of RS modes in accordance with quasi-sinusoidal rules. Typically, for MoS2 and WS2, when the polarization vector of excited light is along the c axis of the crystal, all RS modes are nearly completely “expunged” from the Raman spectra. The mechanism is that the absorption of most TMDs with a space group of R3m for the light polarized along the c axis is infinitesimal, thus forming a small coupling intensity of electronic states excited optically and acoustic-phonon modes at point M, which in turn restrain the appearance of RS modes. The regulating strategy proposed can be applied to other van der Waals crystals so as to obtain a high signal-to-noise ratio Raman spectrum.
Photonics Research
- Publication Date: Oct. 12, 2018
- Vol. 6, Issue 11, 11000991 (2018)
Terahertz emission from layered GaTe crystal due to surface lattice reorganization and in-plane noncubic mobility anisotropy
Jiangpeng Dong, Kevin-P. Gradwohl, Yadong Xu, Tao Wang, Binbin Zhang, Bao Xiao, Christian Teichert, and Wanqi Jie
In this work, a model based on the optical rectification effect and the photocurrent surge effect is proposed to describe the terahertz emission mechanism of the layered GaTe crystal. As a centrosymmetric crystal, the optical rectification effect arises from the breaking of the inversion symmetry due to lattice reorganization of the crystal’s surface layer. In addition, the photocurrent surge originating from the unidirectional charge carrier diffusion—due to the noncubic mobility anisotropy within the layers—produces terahertz radiation. This is confirmed by both terahertz emission spectroscopy and electric property characterization. The current surge perpendicular to the layers also makes an important contribution to the terahertz radiation, which is consistent with its incident angle dependence. Based on our results, we infer that the contribution of optical rectification changes from 90% under normal incidence to 23% under a 40° incidence angle. The results not only demonstrate the terahertz radiation properties of layered GaTe bulk crystals, but also promise the potential application of terahertz emission spectroscopy for characterizing the surface properties of layered materials. In this work, a model based on the optical rectification effect and the photocurrent surge effect is proposed to describe the terahertz emission mechanism of the layered GaTe crystal. As a centrosymmetric crystal, the optical rectification effect arises from the breaking of the inversion symmetry due to lattice reorganization of the crystal’s surface layer. In addition, the photocurrent surge originating from the unidirectional charge carrier diffusion—due to the noncubic mobility anisotropy within the layers—produces terahertz radiation. This is confirmed by both terahertz emission spectroscopy and electric property characterization. The current surge perpendicular to the layers also makes an important contribution to the terahertz radiation, which is consistent with its incident angle dependence. Based on our results, we infer that the contribution of optical rectification changes from 90% under normal incidence to 23% under a 40° incidence angle. The results not only demonstrate the terahertz radiation properties of layered GaTe bulk crystals, but also promise the potential application of terahertz emission spectroscopy for characterizing the surface properties of layered materials.
Photonics Research
- Publication Date: Apr. 15, 2019
- Vol. 7, Issue 5, 05000518 (2019)
Adaptive cavity-enhanced dual-comb spectroscopy
Weipeng Zhang, Xinyi Chen, Xuejian Wu, Yan Li, and Haoyun Wei
Resolution and bandwidth are critical for cavity-enhanced dual-comb spectroscopy (CE-DCS). Here, we pioneer an adaptive approach in CE-DCS to improve the broadband as well as the resolution. Postcorrections to dual-comb interferograms adaptively compensate the relative phase jitters of the optical frequency combs and result in both a mode-resolved spectral resolution and a signal-to-noise ratio of 440:1 in 1 s. Meanwhile, an adaptive comb-cavity locking scheme exploits more than 90% of the comb modes, covering 340 cm 1 (10 THz) at 6450 cm 1. For a single dual-comb interferogram, more than 40,000 comb teeth spaced by 250 MHz are measured in less than 7.5 ms, contributing to a noise equivalent absorption per spectral element of 2×10 10 cm 1 ·Hz 1/2. This adaptive cavity-enhanced dual-comb spectroscopy technique provides an attractive spectroscopic tool that may be utilized in trace-gas sensing, breath and cancer analysis, and engine combustion diagnosis. Resolution and bandwidth are critical for cavity-enhanced dual-comb spectroscopy (CE-DCS). Here, we pioneer an adaptive approach in CE-DCS to improve the broadband as well as the resolution. Postcorrections to dual-comb interferograms adaptively compensate the relative phase jitters of the optical frequency combs and result in both a mode-resolved spectral resolution and a signal-to-noise ratio of 440:1 in 1 s. Meanwhile, an adaptive comb-cavity locking scheme exploits more than 90% of the comb modes, covering 340 cm 1 (10 THz) at 6450 cm 1. For a single dual-comb interferogram, more than 40,000 comb teeth spaced by 250 MHz are measured in less than 7.5 ms, contributing to a noise equivalent absorption per spectral element of 2×10 10 cm 1 ·Hz 1/2. This adaptive cavity-enhanced dual-comb spectroscopy technique provides an attractive spectroscopic tool that may be utilized in trace-gas sensing, breath and cancer analysis, and engine combustion diagnosis.
Photonics Research
- Publication Date: Jul. 23, 2019
- Vol. 7, Issue 8, 08000883 (2019)
Facilitated tip-enhanced Raman scattering by focused gap-plasmon hybridization
Houkai Chen, Yuquan Zhang, Yanmeng Dai, Changjun Min, Siwei Zhu, and Xiaocong Yuan
Tip-enhanced Raman scattering (TERS) spectroscopy is a nondestructive and label-free molecular detection approach that provides high sensitivity and nanoscale spatial resolution. Therefore, it has been used in a wide array of applications. We demonstrate a gap-plasmon hybridization facilitated by a bottom-illuminated TERS configuration. The gap-plasmon hybridization effect is first performed with the finite-difference time-domain method to optimize the parameters, and experiments are then conducted to calibrate the performance. The results demonstrate an enhancement factor of 1157 and a spatial resolution of 13.5 nm. The proposed configuration shows great potential in related surface imaging applications in various fields of research. Tip-enhanced Raman scattering (TERS) spectroscopy is a nondestructive and label-free molecular detection approach that provides high sensitivity and nanoscale spatial resolution. Therefore, it has been used in a wide array of applications. We demonstrate a gap-plasmon hybridization facilitated by a bottom-illuminated TERS configuration. The gap-plasmon hybridization effect is first performed with the finite-difference time-domain method to optimize the parameters, and experiments are then conducted to calibrate the performance. The results demonstrate an enhancement factor of 1157 and a spatial resolution of 13.5 nm. The proposed configuration shows great potential in related surface imaging applications in various fields of research.
Photonics Research
- Publication Date: Jan. 07, 2020
- Vol. 8, Issue 2, 02000103 (2020)
Lamellar hafnium ditelluride as an ultrasensitive surface-enhanced Raman scattering platform for label-free detection of uric acid
Yang Li, Haolin Chen, Yanxian Guo, Kangkang Wang, Yue Zhang, Peilin Lan, Jinhao Guo, Wen Zhang, Huiqing Zhong, Zhouyi Guo, Zhengfei Zhuang, and Zhiming Liu
The development of two-dimensional (2D) transition metal dichalcogenides has been in a rapid growth phase for the utilization in surface-enhanced Raman scattering (SERS) analysis. Here, we report a promising 2D transition metal tellurides (TMTs) material, hafnium ditelluride (HfTe2), as an ultrasensitive platform for Raman identification of trace molecules, which demonstrates extraordinary SERS activity in sensitivity, uniformity, and reproducibility. The highest Raman enhancement factor of 2.32×106 is attained for a rhodamine 6G molecule through the highly efficient charge transfer process at the interface between the HfTe2 layered structure and the adsorbed molecules. At the same time, we provide an effective route for large-scale preparation of SERS substrates in practical applications via a facile stripping strategy. Further application of the nanosheets for reliable, rapid, and label-free SERS fingerprint analysis of uric acid molecules, one of the biomarkers associated with gout disease, is performed, which indicates arresting SERS signals with the limits of detection as low as 0.1 mmol/L. The study based on this type of 2D SERS substrate not only reveals the feasibility of applying TMTs to SERS analysis, but also paves the way for nanodiagnostics, especially early marker detection. The development of two-dimensional (2D) transition metal dichalcogenides has been in a rapid growth phase for the utilization in surface-enhanced Raman scattering (SERS) analysis. Here, we report a promising 2D transition metal tellurides (TMTs) material, hafnium ditelluride (HfTe2), as an ultrasensitive platform for Raman identification of trace molecules, which demonstrates extraordinary SERS activity in sensitivity, uniformity, and reproducibility. The highest Raman enhancement factor of 2.32×106 is attained for a rhodamine 6G molecule through the highly efficient charge transfer process at the interface between the HfTe2 layered structure and the adsorbed molecules. At the same time, we provide an effective route for large-scale preparation of SERS substrates in practical applications via a facile stripping strategy. Further application of the nanosheets for reliable, rapid, and label-free SERS fingerprint analysis of uric acid molecules, one of the biomarkers associated with gout disease, is performed, which indicates arresting SERS signals with the limits of detection as low as 0.1 mmol/L. The study based on this type of 2D SERS substrate not only reveals the feasibility of applying TMTs to SERS analysis, but also paves the way for nanodiagnostics, especially early marker detection.
Photonics Research
- Publication Date: May. 25, 2021
- Vol. 9, Issue 6, 06001039 (2021)
Ultra-wide-dynamic-range gas sensing by optical pathlength multiplexed absorption spectroscopy
Xiutao Lou, Yabo Feng, Shunhu Yang, and Yongkang Dong
Laser absorption spectroscopy (LAS) has become the most widely used laser spectroscopic technique for gas detection due to its capability of accurate quantification and straightforward operation. However, since resolving weak absorption and averting over-absorption are always mutually exclusive, the dynamic range of the LAS-based gas sensor is limited and insufficient for many applications in fundamental study and industry. To overcome the limitation on the dynamic range, this article reports optical pathlength (OPL) multiplexed absorption spectroscopy using a gas cell having multiple internal reflections. It organically fuses together the transmission and reflection operation modes: the former directly uses the entire OPL of the gas cell, while the latter interrogates different internal short OPLs by optical interferometry, yielding >100-fold OPL variation. The achieved dynamic range is more than 6 orders of magnitude that surpasses other LAS techniques by 2–3 orders of magnitude. The proposed method promotes a novel way for the development of large-dynamic-range spectroscopic gas sensors for fundamental studies and industrial applications. Laser absorption spectroscopy (LAS) has become the most widely used laser spectroscopic technique for gas detection due to its capability of accurate quantification and straightforward operation. However, since resolving weak absorption and averting over-absorption are always mutually exclusive, the dynamic range of the LAS-based gas sensor is limited and insufficient for many applications in fundamental study and industry. To overcome the limitation on the dynamic range, this article reports optical pathlength (OPL) multiplexed absorption spectroscopy using a gas cell having multiple internal reflections. It organically fuses together the transmission and reflection operation modes: the former directly uses the entire OPL of the gas cell, while the latter interrogates different internal short OPLs by optical interferometry, yielding >100-fold OPL variation. The achieved dynamic range is more than 6 orders of magnitude that surpasses other LAS techniques by 2–3 orders of magnitude. The proposed method promotes a novel way for the development of large-dynamic-range spectroscopic gas sensors for fundamental studies and industrial applications.
Photonics Research
- Publication Date: Jan. 26, 2021
- Vol. 9, Issue 2, 02000193 (2021)
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