Damage dynamics and relaxation process of double pulses with nanosecond laser
Qiaofei Pan, Ke Wang, Jiaqi Han, and Bin Ma
The laser-induced damage threshold (LIDT) of optical elements is a critical limitation in advancing next-generation spaceborne laser technologies. Transient mechanisms in multiple-pulse damage dynamics have been recognized, but significant gaps remain in understanding these processes. In this study, we introduce a practice time interval (Δtp)-dependent damage metric. Using a double-pulse double-probe experimental configuration, we systematically examine the double-pulse damage dynamics and relaxation process. The first pulse induces localized modifications that initiate a relaxation process, accumulating material damage caused by the subsequent pulse. Our results show that this relaxation lasts ∼500 ns for surface damage and is on a several millisecond scale for bulk damage. The second pulse induces more pronounced modifications and damage when Δtp is less than 100 ns, dominated by nonlinear phenomena like multiphoton absorption due to temporally overlapping pulses. Conversely, for Δtp>100 ns, thermal accumulation via phonon relaxation predominates. Additionally, the critical energy density for damage correlates positively with LIDT as Δtp increases, reflecting the reduced thermal and mechanical stress influence. These findings highlight the dynamic competition between nonlinear and thermal effects in multiple-pulse laser interactions, providing practical strategies for designing optical components with high damage thresholds and developing high-performance optical systems.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2246 (2025)
  • DOI:10.1364/PRJ.539648
Grating mediated by three-dimensional director solitons
Chao-Yi Li, Xing-Zhou Tang, Zhi-Jun Huang, Ge Sun..., Ze-Yu Wang, Yuan Liu, Bing-Xiang Li, Juan J. de Pablo and Yan-Qing Lu|Show fewer author(s)
Within the realm of soft matter, particularly liquid crystals, the ability to leverage material properties to create switchable diffraction gratings holds significant importance in disciplines such as optics and information science. However, designing switchable patterns and compiling information based on output images remain challenging. Here, we introduce an approach to address these limitations by designing switchable gratings mediated by three-dimensional director solitons. We utilize photo-patterning, employing lithography systems with different ultraviolet light, to fabricate the desired patterns. This method allows solitons to nucleate and localize within the regions of the pattern where the anchoring energy is weaker. The periodic structures, alternating between solitons and uniform patterns, exhibit the ability to diffract light beams. By switching the voltage, we can control the generation and localization of solitons within periodic patterns and realize switching between the waveplate and grating. Our experimental findings, complemented by simulation outcomes, validate the feasibility of utilizing three-dimensional solitons in optical applications.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2240 (2025)
  • DOI:10.1364/PRJ.546820
Cascaded Raman lasing in a lithium tetraborate whispering gallery mode resonator
Chengcai Tian, Jervee Punzalan, Petra Becker, Ladislav Bohatý..., Keith C. Gordon, Richard Blaikie, Harald G. L. Schwefel and Florian Sedlmeir|Show fewer author(s)
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2232 (2025)
  • DOI:10.1364/PRJ.560671
Fringe projection profilometry via LED array with pre-calibration
Jin Tan, Bo Zhang, Hong-Xu Huang, Wei-Jie Deng, and Ming-Jie Sun
Fringe projection profilometry (FPP) is a method that determines height by analyzing distortional fringes, which is widely used in high-accuracy 3D imaging. Now, one major reason limiting imaging speed in FPP is the projection device; the capture speed of high-speed cameras far exceeds the projection frequency. Among various devices, an LED array can exceed the speed of a high-speed camera. However, non-sinusoidal fringe patterns in the LED array systems can arise from several factors that will reduce the accuracy, such as the spacing between adjacent LEDs, the inconsistency in brightness across different LEDs, and the residual high-order harmonics in binary defocusing projection. It is challenging to resolve by other methods. In this paper, we propose a method that creates a look-up table using system calibration data of phase-height models. Then we utilize the look-up table to compensate for the phase error during the reconstructing process. The foundation of the proposed method relies on the time-invariance of systematic error; any factor that impacts the sinusoidal characteristic would present as an anomaly in the unwrapped phase. Experiments have demonstrated that the root mean square errors (RMSEs) of the results yielded by the proposed method were reduced by over 90% compared to those yielded by the traditional method, reaching 20 μm accuracy. This paper offers an alternative approach for high-speed and high-accuracy 3D imaging with an LED array and presents a workable solution for addressing complex errors from non-sinusoidal fringes.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2224 (2025)
  • DOI:10.1364/PRJ.560762
Observation of coexisting large-area topological pseudospin and valley waveguide states in a planar microstrip heterostructure based on topological LC circuits
Yaoyao Shu, Mina Ren, Xin Qi, Zhiwei Guo..., Haitao Jiang, Yaping Yang, Hong Chen and Yong Sun|Show fewer author(s)
The rapid development of topological photonics has significantly facilitated the development of novel microwave and optical devices with richer electromagnetic properties. A stable and efficient guided wave is a necessary condition for optical information transmission and processing. However, most topological waveguides are confined at a domain wall around the interfaces and usually operate in a single-type topological mode, leading to low-throughput energy transmission over a single frequency band. Here, we propose, design, and experimentally demonstrate a novel planar microstrip heterostructure system based on topological LC circuits that supports a dual-type topological large-area waveguide state, and the system showcases tunable mode widths with different operating bandwidths. Inheriting from the pseudospin and valley topology, the topological large-area waveguides exhibit the pseudospin- and valley-locked properties at different frequency windows and have strong robustness against defects. Moreover, the large-area topological waveguide states of high-energy capacity channel intersections and beam expanders with topological pseudospin and valley mode width degrees of freedom are verified numerically and experimentally. We also show the distinct topological origins of large-area topological waveguide states that provide versatile signal routing paths by their intrinsic coupling properties. Our system provides an efficient scheme to realize the tunable width and the multi-mode bandwidth of topological waveguides, which can further promote the applications of multi-functional high-performance topological photonic integrated circuit systems in on-chip communication and signal processing.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2213 (2025)
  • DOI:10.1364/PRJ.561253
Deep learning assisted real-time and portable refractometer using a π-phase-shifted tilted fiber Bragg grating sensor
Ziqi Liu, Chang Liu, Tuan Guo, Zhaohui Li, and Zhengyong Liu
In this work, we demonstrate a π-phase-shifted tilted fiber Bragg grating (π-PSTFBG)-based sensor for measuring the refractive index (RI) of NaCl solutions, achieving a real-time and online measurement system by employing a densely connected convolutional neural network (D-CNN) model to demodulate the full spectrum. The proposed π-PSTFBG sensor is prepared by using the advanced fiber grating inscription system based on a two-beam interferometry method, which could introduce deeper features of dip-splitting for all the lossy dips in the spectrum, giving the possibility of fully measuring the change of RI. This enhanced feature gives relatively higher prediction accuracy (R2 of 99.67%) using the well-trained D-CNN model compared with the results achieved by pure TFBG or that with a gold coating. As a further demonstration from a practical view, a prototype integrated with the proposed D-CNN algorithm is developed to conduct RI measurement of NaCl solutions in real time using a π-PSTFBG-based RI sensor. The results show that the proposed real-time demodulation system is capable of measuring RI with an average error of 1.6×10-4 RIU in a short response time of <1 s. The demonstrated spectral demodulation approach powered by deep learning shows great potential in real-time analysis for chemical solutions and point-of-care medical testing based on RI changes, especially for the portable requirements.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2202 (2025)
  • DOI:10.1364/PRJ.561101
Synchronous dynamics of passively synchronized Yb-doped fiber lasers
Fan Wu, Zexin Zhang, Jinrong Tian, Pengxiang Zhang..., Lin Mao, Yuze Zhan, Yaxuan Li and Yanrong Song|Show fewer author(s)
A tightly synchronized fiber laser system composed of two mode-locked Yb-doped fiber lasers in a master-slave configuration is built. The synchronization could sustain for more than 6 h, and the maximum tolerance of cavity length mismatch is measured to be about 210 μm. Afterward, a time-stretch dispersive Fourier transform technique is introduced to analyze the synchronization process over multiple cycles. The pulse evolution, center wavelength shift, spectral reshaping, and broadening are all clearly detected. And the synchronization time is experimentally determined on the order of microseconds (hundreds of roundtrips). These results also show the seed pulse acting as a temporal gate for mode locking in some cases. To the best of our knowledge, this is the first time that pulse formation, spectral evolution, center wavelength shift, and synchronization time during the synchronization process are precisely revealed in experiment. These results would help to improve the performances of synchronized laser devices and deeply understand the mechanisms of the synchronization process and other light-light interactions in materials.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2192 (2025)
  • DOI:10.1364/PRJ.562023
Enhancement of superchirality induced by matching electromagnetic components of the combined field
Zhishang Wang, Jing Guo, Qian Shou, Wei Hu, and Daquan Lu
We propose an approach for generating the enhanced superchiral needle by matching electromagnetic components of the combined field, which is the superposition of a radially polarized vortex Bessel–Gaussian beam (RPVBGB) and an azimuthally polarized Bessel–Gaussian beam (APBGB). In the tightly focused combined field, the longitudinal magnetic component provided by the APBGB, together with the longitudinal electric component provided by the RPVBGB, induces an additional contribution to the optical chirality and thereby significantly improves the enhancement factor of the superchiral needle. It is revealed that the characteristics of the superchiral needle are mainly influenced by the ring aperture, the phase difference, and the amplitude ratio. Under proper parameters, the enhancement factor can reach from 22.9 to 32.9, and the needle width can reach from 0.0151λ to 0.0043λ and from 0.0182λ to 0.0058λ in the x- and y-directions, respectively. The results would be of interest for the chirality measurement of individual molecules.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2184 (2025)
  • DOI:10.1364/PRJ.562266
Non-line-of-sight imaging via scalable scattering mapping using TOF cameras
Yujie Fang, Junming Wu, Shengming Zhong, Xiaofeng Zhang..., Yulei An, Xia Wang, Binghua Su and Kejun Wang|Show fewer author(s)
The technique of imaging or tracking objects outside the field of view (FOV) through a reflective relay surface, usually called non-line-of-sight (NLOS) imaging, has been a popular research topic in recent years. Although NLOS imaging can be achieved through methods such as detector design, optical path inverse operation algorithm design, or deep learning, challenges such as high costs, complex algorithms, and poor results remain. This study introduces a simple algorithm-based rapid depth imaging device, namely, the continuous-wave time-of-flight range imaging camera (CW-TOF camera), to address the decoupled imaging challenge of differential scattering characteristics in an object-relay surface by quantifying the differential scattering signatures through statistical analysis of light propagation paths. A scalable scattering mapping (SSM) theory has been proposed to explain the degradation process of clear images. High-quality NLOS object 3D imaging has been achieved through a data-driven approach. To verify the effectiveness of the proposed algorithm, experiments were conducted using an optical platform and real-world scenarios. The objects on the optical platform include plaster sculptures and plastic letters, while relay surfaces consist of polypropylene (PP) plastic boards, acrylic boards, and standard Lambertian diffusers. In real-world scenarios, the object is clothing, with relay surfaces including painted doors and white plaster walls. Imaging data were collected for different combinations of objects and relay surfaces for training and testing, totaling 210,000 depth images. The reconstruction of NLOS images in the laboratory and real-world is excellent according to subjective evaluation; thus, our approach can realize NLOS imaging in harsh natural scenes and advances the practical application of NLOS imaging.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2172 (2025)
  • DOI:10.1364/PRJ.558736
Continuously tunable topological negative refraction via a tailorable Bloch wavevector in momentum space
Yidong Zheng, Jianfeng Chen, Zitao Ji, and Zhi-Yuan Li
Topological photonics provides a strategy that makes light transmission immune to structural-defects-induced backward scattering. Leveraging this, topological negative refraction enables robust, reflectionless light deflection, but directly controlling the refraction direction remains challenging. We demonstrate continuously tunable topological negative refraction at the interface between a one-way waveguide state and a free-space beam, overcoming the limitations of fixed refraction angles in conventional systems. The key insight is the ability to adjust the wavevector of the incident one-way waveguide state. Through manipulating the Bloch wavevector of the waveguide states in momentum space, we achieve a transition from negative to positive refraction. The unidirectional nature of these states prevents backscattering from defects, ensuring immunity to imperfections. As a prototypical demonstration, we achieve dynamic steering of refraction beams from -38° to +12° through active magnetic bias control. Our findings provide an exotic pathway for photon manipulation and a promising route toward topological photonics applications.
  • Jul. 25, 2025
  • Photonics Research
  • Vol. 13, Issue 8, 2159 (2025)
  • DOI:10.1364/PRJ.560388
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