Superresolution measurement of thermo-optic coefficient of KTP crystals based on phase amplification
Wuzhen Li, Zhiyuan Zhou, Guangcan Guo, and Baosen Shi
In this work, we achieve a fourfold enhancement in thermo-optic coefficient measurement resolution for KTiOPO4 crystal using a self-stabilized birefringence interferometer integrated with cascaded second-harmonic generation. We observe the tunable interference beating phenomenon by rotating a birefringent crystal versus the temperature of the crystal. Furthermore, the fourth-harmonic interference fringes beat 4 times faster than the fundamental wave interference fringes. This beating effect is used to determine the thermo-optic coefficients of the two principal refractive axes with a single measurement. This work provides a feasible, real-time, and robust method for superresolution measurements based on birefringence interferometry.In this work, we achieve a fourfold enhancement in thermo-optic coefficient measurement resolution for KTiOPO4 crystal using a self-stabilized birefringence interferometer integrated with cascaded second-harmonic generation. We observe the tunable interference beating phenomenon by rotating a birefringent crystal versus the temperature of the crystal. Furthermore, the fourth-harmonic interference fringes beat 4 times faster than the fundamental wave interference fringes. This beating effect is used to determine the thermo-optic coefficients of the two principal refractive axes with a single measurement. This work provides a feasible, real-time, and robust method for superresolution measurements based on birefringence interferometry.
- Jun. 24, 2025
- Chinese Optics Letters
- Vol. 23, Issue 8, 081201 (2025)
- DOI：10.3788/COL202523.081201
Machine learning phase control of filled-aperture coherent beam combining: principle and numerical demonstration
Hongbing Zhou, Rumao Tao, Xi Feng, Haoyu Zhang, Min Li, Xiong Xin, Yuyang Peng, Honghuan Lin, Jianjun Wang, Lixin Yan, and Feng Jing
Machine learning has already shown promising potential in tiled-aperture coherent beam combining (CBC) to achieve versatile advanced applications. By sampling the spatially separated laser array before the combiner and detuning the optical path delays, deep learning techniques are incorporated into filled-aperture CBC to achieve single-step phase control. The neural network is trained with far-field diffractive patterns at the defocus plane to establish one-to-one phase-intensity mapping, and the phase prediction accuracy is significantly enhanced thanks to the strategies of sin-cos loss function and two-layer output of the phase vector that are adopted to resolve the phase discontinuity issue. The results indicate that the trained network can predict phases with improved accuracy, and phase-locking of nine-channel filled-aperture CBC has been numerically demonstrated in a single step with a residual phase of λ/70. To the best of our knowledge, this is the first time that machine learning has been made feasible in filled-aperture CBC laser systems.Machine learning has already shown promising potential in tiled-aperture coherent beam combining (CBC) to achieve versatile advanced applications. By sampling the spatially separated laser array before the combiner and detuning the optical path delays, deep learning techniques are incorporated into filled-aperture CBC to achieve single-step phase control. The neural network is trained with far-field diffractive patterns at the defocus plane to establish one-to-one phase-intensity mapping, and the phase prediction accuracy is significantly enhanced thanks to the strategies of sin-cos loss function and two-layer output of the phase vector that are adopted to resolve the phase discontinuity issue. The results indicate that the trained network can predict phases with improved accuracy, and phase-locking of nine-channel filled-aperture CBC has been numerically demonstrated in a single step with a residual phase of λ/70. To the best of our knowledge, this is the first time that machine learning has been made feasible in filled-aperture CBC laser systems.
- Jun. 24, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 3, 03000e39 (2025)
- DOI：10.1017/hpl.2025.24
Bacterial identification by metabolite-level interpretable surface-enhanced Raman spectroscopy
Haoran Chen, Ruike Zhao, Xinyuan Bi, Nan Shen, Xi Mo, Yue Tao, Zhou Chen, and Jian Ye
Surface-enhanced Raman spectroscopy (SERS), as a great potential label-free tool in metabolite detection, offers a strategy for rapid bacterial identification. However, it still lacks experimentally supported spectral interpretation at the metabolite level for complex biosamples. We present a SERS-based method for reliable bacterial intracellular metabolic profiling using plasmonic colloids with high rapidness and cost-efficiency. A convolutional neural network model was constructed to accurately classify eight types of bacteria with an overall accuracy as high as 90.44% and identify the key spectral features for classification by Shapley Additive Explanations. Molecule-level interpretation of the SERS metabolic profiles has been further realized in combination with laser desorption/ionization mass spectrometry, evidencing the primary metabolite contribution to the bacterial spectral signatures and molecule-level distinctions among different bacterial types. We provide insights into the mechanism of bacterial identification by label-free SERS and pave the way for interpretable SERS diagnostic tools for various diseases.Surface-enhanced Raman spectroscopy (SERS), as a great potential label-free tool in metabolite detection, offers a strategy for rapid bacterial identification. However, it still lacks experimentally supported spectral interpretation at the metabolite level for complex biosamples. We present a SERS-based method for reliable bacterial intracellular metabolic profiling using plasmonic colloids with high rapidness and cost-efficiency. A convolutional neural network model was constructed to accurately classify eight types of bacteria with an overall accuracy as high as 90.44% and identify the key spectral features for classification by Shapley Additive Explanations. Molecule-level interpretation of the SERS metabolic profiles has been further realized in combination with laser desorption/ionization mass spectrometry, evidencing the primary metabolite contribution to the bacterial spectral signatures and molecule-level distinctions among different bacterial types. We provide insights into the mechanism of bacterial identification by label-free SERS and pave the way for interpretable SERS diagnostic tools for various diseases.
- Jun. 23, 2025
- Advanced Photonics
- Vol. 7, Issue 4, 046007 (2025)
- DOI：10.1117/1.AP.7.4.046007
Dynamic beam shifts via refractive index tuning in photonic crystal slabs
Mingxuan Gu, Xinghong Chen, and Yifei Mao
Light-beam shifts accompanied by propagation between two media show potential in applications such as optical sensing, optical communication, and optical computing. However, existing work tends to focus on the static response of the device, i.e., the beam shift when the structural parameters and incident conditions are fixed. Here, we analyze the dynamics of beam shifting via photonic crystal slabs under refractive index variation. On the one hand, we investigate the trend of cross-polarized phase gradient under small changes in refractive index. Simulation results show that the direction of the beam shift can change by more than 50° for a refractive index change of only 0.06. On the other hand, we study the interaction of incident light with the far-field polarizations of bound states in the continuum in the presence of a refractive index jump in the phase-change material. In this case, simulation results show that the large change in the Pancharatnam–Berry phase gradient causes the beam to move widely, with a change in beam direction of 61.30° and a change in beam displacement of 15 µm. Furthermore, all displacement amounts are comparable to the radius of the incident beam (∼8 µm). Our work provides a new perspective on the study of beam shifts, which can advance practical applications of beam shift in sensing, intelligent detecting, and beam control.Light-beam shifts accompanied by propagation between two media show potential in applications such as optical sensing, optical communication, and optical computing. However, existing work tends to focus on the static response of the device, i.e., the beam shift when the structural parameters and incident conditions are fixed. Here, we analyze the dynamics of beam shifting via photonic crystal slabs under refractive index variation. On the one hand, we investigate the trend of cross-polarized phase gradient under small changes in refractive index. Simulation results show that the direction of the beam shift can change by more than 50° for a refractive index change of only 0.06. On the other hand, we study the interaction of incident light with the far-field polarizations of bound states in the continuum in the presence of a refractive index jump in the phase-change material. In this case, simulation results show that the large change in the Pancharatnam–Berry phase gradient causes the beam to move widely, with a change in beam direction of 61.30° and a change in beam displacement of 15 µm. Furthermore, all displacement amounts are comparable to the radius of the incident beam (∼8 µm). Our work provides a new perspective on the study of beam shifts, which can advance practical applications of beam shift in sensing, intelligent detecting, and beam control.
- Jun. 20, 2025
- Chinese Optics Letters
- Vol. 23, Issue 7, 073602 (2025)
- DOI：10.3788/COL202523.073602
Vascular permeability assessment using dual-wavelength photoacoustic microscopy with spectral unmixing
Yongyan Ren, Kun Yu, Qiansong Xia, Honghui Li, and Liming Nie
Vascular permeability (VP) plays a critical role in liver and kidney fibrosis progression. Traditional VP quantification methods use single-wavelength photoacoustic microscopy (PAM) with Evans Blue (EB) dye, which have limitations including signal attenuation and decreased accuracy. To overcome these issues, we developed a dual-wavelength PAM method with a spectral unmixing algorithm for quantitative VP evaluation in liver and kidney microvasculature. This approach allows for an accurate assessment of VP dynamics by analyzing hemoglobin and EB absorption. Using murine models of fibrosis, we found that fibrosis reduces vessel density and increases vessel diameter, providing valuable insights into VP changes during fibrosis progression.Vascular permeability (VP) plays a critical role in liver and kidney fibrosis progression. Traditional VP quantification methods use single-wavelength photoacoustic microscopy (PAM) with Evans Blue (EB) dye, which have limitations including signal attenuation and decreased accuracy. To overcome these issues, we developed a dual-wavelength PAM method with a spectral unmixing algorithm for quantitative VP evaluation in liver and kidney microvasculature. This approach allows for an accurate assessment of VP dynamics by analyzing hemoglobin and EB absorption. Using murine models of fibrosis, we found that fibrosis reduces vessel density and increases vessel diameter, providing valuable insights into VP changes during fibrosis progression.
- Jun. 20, 2025
- Chinese Optics Letters
- Vol. 23, Issue 7, 071701 (2025)
- DOI：10.3788/COL202523.071701
6 kW near-single-mode monolithic fiber laser employing a longitudinally asymmetric spindle-shaped ytterbium-doped fiber
Fengchang Li, Peng Wang, Xiangming Meng, Baolai Yang, Liangjin Huang, Xiaoming Xi, Hanwei Zhang, Zhiping Yan, Zhiyong Pan, Xiaolin Wang, Zefeng Wang, and Jinbao Chen
In order to balance the suppression of stimulated Raman scattering (SRS) and transverse mode instability (TMI) in high-power fiber lasers, in this Letter, a new type of spindle-shaped ytterbium-doped fiber (YDF) with asymmetric longitude distribution was designed and produced, which had a small-sized input end, large-sized transmission section, and moderate output end, enabling a good fit with a seed laser and mitigating SRS as well as TMI effects. A counter-pumped fiber laser amplifier was established using this YDF, and two kinds of laser diodes (LDs) were adopted for increasing the TMI threshold. Finally, the maximum output power reached 6 kW, and the beam quality (M2 factors) indicated near-single-mode output. The SRS suppression ratio under 6 kW output power was 36 dB, and no dynamic TMI was observed, which revealed that further enhancement of output power was limited only by pump power.In order to balance the suppression of stimulated Raman scattering (SRS) and transverse mode instability (TMI) in high-power fiber lasers, in this Letter, a new type of spindle-shaped ytterbium-doped fiber (YDF) with asymmetric longitude distribution was designed and produced, which had a small-sized input end, large-sized transmission section, and moderate output end, enabling a good fit with a seed laser and mitigating SRS as well as TMI effects. A counter-pumped fiber laser amplifier was established using this YDF, and two kinds of laser diodes (LDs) were adopted for increasing the TMI threshold. Finally, the maximum output power reached 6 kW, and the beam quality (M2 factors) indicated near-single-mode output. The SRS suppression ratio under 6 kW output power was 36 dB, and no dynamic TMI was observed, which revealed that further enhancement of output power was limited only by pump power.
- Jun. 20, 2025
- Chinese Optics Letters
- Vol. 23, Issue 7, 071408 (2025)
- DOI：10.3788/COL202523.071408
Enhancing terahertz imaging with Rydberg atom-based sensors using untrained neural networks
Jun Wan, Bin Zhang, Xianzhe Li, Tao Li, Qirong Huang, Xinyu Yang, Kaiqing Zhang, Wei Huang, and Haixiao Deng
Terahertz (THz) imaging based on the Rydberg atom achieves high sensitivity and frame rates but faces challenges in spatial resolution due to diffraction, interference, and background noise. This study introduces a polarization filter and a deep learning-based method using a physically informed convolutional neural network to enhance resolution without pre-trained datasets. The technique reduces diffraction artifacts and achieves lens-free imaging with a resolution exceeding 1.25 lp/mm over a wide field of view. This advancement significantly improves the imaging quality of the Rydberg atom-based sensor, expanding its potential applications in THz imaging.Terahertz (THz) imaging based on the Rydberg atom achieves high sensitivity and frame rates but faces challenges in spatial resolution due to diffraction, interference, and background noise. This study introduces a polarization filter and a deep learning-based method using a physically informed convolutional neural network to enhance resolution without pre-trained datasets. The technique reduces diffraction artifacts and achieves lens-free imaging with a resolution exceeding 1.25 lp/mm over a wide field of view. This advancement significantly improves the imaging quality of the Rydberg atom-based sensor, expanding its potential applications in THz imaging.
- Jun. 20, 2025
- Chinese Optics Letters
- Vol. 23, Issue 7, 071104 (2025)
- DOI：10.3788/COL202523.071104
Fabrication of ultra-low-absorption thin films via ion beam-assisted electron-beam evaporation
Ruichen Song, Jiaqi Hu, Yunqi Peng, Ying’ao Xiao, Yuxiang Wang, Kongxu Zhu, Yuheng Jiang, Xusheng Xia, and Zhilin Xia
High-power laser systems require thin films with extremely low absorption. Ultra-low-absorption films are often fabricated via ion beam sputtering, which is costly and slow. This study analyzes the impact of doping titanium and annealing on the absorption characteristics of thin films, focusing on composition and structure. The results indicate that the primary factor influencing absorption is composition. Suppressing the presence of electrons or holes that do not form stable chemical bonds can significantly reduce absorption; for amorphous thin films, the structural influence on absorption is relatively minor. Thus, composition control is crucial for fabricating ultra-low-absorption films, while the deposition method is secondary. Ion beam-assisted electron-beam evaporation, which is relatively seldom used for fabricating low-absorption films, was employed to produce high-reflectivity films. After annealing, the absorption at 1064 nm reached 1.70 parts per million. This method offers a cost-effective and rapid approach for fabricating ultra-low-absorption films.High-power laser systems require thin films with extremely low absorption. Ultra-low-absorption films are often fabricated via ion beam sputtering, which is costly and slow. This study analyzes the impact of doping titanium and annealing on the absorption characteristics of thin films, focusing on composition and structure. The results indicate that the primary factor influencing absorption is composition. Suppressing the presence of electrons or holes that do not form stable chemical bonds can significantly reduce absorption; for amorphous thin films, the structural influence on absorption is relatively minor. Thus, composition control is crucial for fabricating ultra-low-absorption films, while the deposition method is secondary. Ion beam-assisted electron-beam evaporation, which is relatively seldom used for fabricating low-absorption films, was employed to produce high-reflectivity films. After annealing, the absorption at 1064 nm reached 1.70 parts per million. This method offers a cost-effective and rapid approach for fabricating ultra-low-absorption films.
- Jun. 19, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 3, 03000e38 (2025)
- DOI：10.1017/hpl.2025.27
A rasterization-based ray-tracing method for laser–plasma interactions
Tao Tao, Zhujun Li, Kejian Qian, Xian Jiang, Guannan Zheng, Rui Yan, Haoran Liu, Qing Jia, Jun Li, Hang Ding, and Jian Zheng
This paper introduces a novel ray-tracing methodology for various gradient-index materials, particularly plasmas. The proposed approach utilizes adaptive-step Runge–Kutta integration to compute ray trajectories while incorporating an innovative rasterization step for ray energy deposition. By removing the requirement for rays to terminate at cell interfaces – a limitation inherent in earlier cell-confined approaches – the numerical formulation of ray motion becomes independent of specific domain geometries. This facilitates a unified and concise tracing method compatible with all commonly used curvilinear coordinate systems in laser–plasma simulations, which were previously unsupported or prohibitively complex under cell-confined frameworks. Numerical experiments demonstrate the algorithm’s stability and versatility in capturing diverse ray physics across reduced-dimensional planar, cylindrical and spherical coordinate systems. We anticipate that the rasterization-based approach will pave the way for the development of a generalized ray-tracing toolkit applicable to a broad range of fluid simulations and synthetic optical diagnostics.This paper introduces a novel ray-tracing methodology for various gradient-index materials, particularly plasmas. The proposed approach utilizes adaptive-step Runge–Kutta integration to compute ray trajectories while incorporating an innovative rasterization step for ray energy deposition. By removing the requirement for rays to terminate at cell interfaces – a limitation inherent in earlier cell-confined approaches – the numerical formulation of ray motion becomes independent of specific domain geometries. This facilitates a unified and concise tracing method compatible with all commonly used curvilinear coordinate systems in laser–plasma simulations, which were previously unsupported or prohibitively complex under cell-confined frameworks. Numerical experiments demonstrate the algorithm’s stability and versatility in capturing diverse ray physics across reduced-dimensional planar, cylindrical and spherical coordinate systems. We anticipate that the rasterization-based approach will pave the way for the development of a generalized ray-tracing toolkit applicable to a broad range of fluid simulations and synthetic optical diagnostics.
- Jun. 18, 2025
- High Power Laser Science and Engineering
- Vol. 13, Issue 3, 03000e37 (2025)
- DOI：10.1017/hpl.2025.22
Ultra-wideband high-speed wavelength-swept DFB laser array and precision measurement system of nonlinear wavelength variations
Yaqiang Fan, Pan Dai, Zhenxing Sun, Yuan Lv, Wei Yuan, Haolin Xia, Jingxuan Zhang, Junwei Dong, Jihong Xu, Jie Zeng, Feng Wang, and Xiangfei Chen
In this study, we developed a robust, ultra-wideband, and high-speed wavelength-swept distributed feedback (DFB) laser array with an 8×3 matrix interleaving structure with no movable or fragile optical components. This wavelength-swept laser (WSL) achieves a continuous (gap-free) wavelength sweeping range of 60 nm and a rapid sweeping speed of 82.7 kHz, marking the widest wavelength sweeping range reported to date for high-speed WSLs based on DFB laser arrays, to our knowledge. To achieve the high-precision mapping from the time domain to the frequency domain, a nonlinear wavelength and frequency variation measurement system based on dual Fabry–Perot (F-P) etalons is designed. The system accurately measures the dynamic relationship of frequency variations over time, enabling precise wavelength interrogation. The proposed WSL was applied to the fiber Bragg grating (FBG) sensor interrogation system. In the high-low temperature and strain experiments, the system performed real-time dynamic interrogation of FBGs for up to 3 h. The experimental results demonstrated good relative accuracy and excellent interrogation performance of the system. In the vibration experiment, the system achieved high-precision interrogation of FBG sensors for high-frequency sinusoidal vibrations up to 8 kHz. Furthermore, the system worked stably under strong vibrations and shocks. Thus, the proposed WSL is applicable to high-speed FBG sensing and optical coherence tomography applications.In this study, we developed a robust, ultra-wideband, and high-speed wavelength-swept distributed feedback (DFB) laser array with an
- Jun. 18, 2025
- Photonics Research
- Vol. 13, Issue 7, 1855 (2025)
- DOI：10.1364/PRJ.545701
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Jun. 21, 2025
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Structured light: fundamentals and applications (2025)
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