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Photonics
Volume 12
Issue 6
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Photonics, Volume 12, Issue 6 (June 2025) – 101 articles

Cover Story (view full-size image): Liquid crystal Spatial Light Modulators are programmable adaptive optics with a broad range of applications, which now include wavefront optimisation in laser-material processing. Until recently, however, due to residual thermal effects, the maximum average power up to which full phase response was possible was limited to ~120 W, with a Gaussian intensity profile. Here, we present experimental results on the operation and performance of an SLM exposed to significantly higher beam powers from a single-mode fibre laser. Our results demonstrate a first-order diffraction efficiency of 0.98 ± 0.01 at 300 W and a phase range of > 2π up to 383 W. Numerical modelling of the thermal response closely matches that measured experimentally. We then also present results of efficient laser surface modification of mild steel, and of molybdenum, up to 350 W. View this paper
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13 pages, 3937 KiB  
Article
A 5 Gb/s Optoelectronic Receiver IC in 180 nm CMOS for Short-Distance Optical Interconnects
by Yunji Song and Sung-Min Park
Photonics 2025, 12(6), 624; https://doi.org/10.3390/photonics12060624 - 19 Jun 2025
Viewed by 264
Abstract
This paper presents a CMOS-based optoelectronic receiver integrated circuit (CORIC) realized in a standard 180 nm CMOS technology for the applications of short-distance optical interconnects. The CORIC comprises a spatially modulated P+/N-well on-chip avalanche photodiode (P+/NW APD) for optical-to-electrical [...] Read more.
This paper presents a CMOS-based optoelectronic receiver integrated circuit (CORIC) realized in a standard 180 nm CMOS technology for the applications of short-distance optical interconnects. The CORIC comprises a spatially modulated P+/N-well on-chip avalanche photodiode (P+/NW APD) for optical-to-electrical conversion, a dummy APD at the differential input for enhanced common-mode noise rejection, a cross-coupled differential transimpedance amplifier (CCD-TIA) for current-to-voltage conversion, a 3-bit continuous-time linear equalizer (CTLE) for adaptive equalization by using NMOS registers, and a fT-doubler output buffer (OB). The CTLE and fT-doubler OB combination not only compensates the frequency-dependent signal loss, but also provides symmetric differential output signals. Post-layout simulations of the proposed CORIC reveal a transimpedance gain of 53.2 dBΩ, a bandwidth of 4.83 GHz even with a 490 fF parasitic capacitance from the on-chip P+/NW APD, a dynamic range of 60 dB that handles the input photocurrents from 1 μApp to 1 mApp, and a DC power consumption of 33.7 mW from a 1.8 V supply. The CORIC chip core occupies an area of 260 × 101 μm2. Full article
(This article belongs to the Special Issue New Insights in Low-Dimensional Optoelectronic Materials and Devices)
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19 pages, 5033 KiB  
Article
Development and Verification of Sampling Timing Jitter Noise Suppression System for Phasemeter
by Tao Yu, Ke Xue, Hongyu Long, Mingzhong Pan, Zhi Wang and Yunqing Liu
Photonics 2025, 12(6), 623; https://doi.org/10.3390/photonics12060623 - 19 Jun 2025
Viewed by 232
Abstract
As the primary electronic payload of laser interferometry system for space gravitational wave detection, the core function of the phasemeter is ultra-high precision phase measurement. According to the principle of laser heterodyne interferometry and the requirement of 1 pm ranging accuracy of the [...] Read more.
As the primary electronic payload of laser interferometry system for space gravitational wave detection, the core function of the phasemeter is ultra-high precision phase measurement. According to the principle of laser heterodyne interferometry and the requirement of 1 pm ranging accuracy of the phasemeter, the phase measurement noise should reach 2π μrad/Hz1/2@(0.1 mHz–1 Hz). The heterodyne interference signal first passes through the quadrant photoelectric detector (QPD) to achieve photoelectric conversion, then passes through the analog-to-digital converter (ADC) to achieve analog and digital conversion, and finally passes through the digital phase-locked loop (DPLL) for phase locking. The sampling timing jitter of the heterodyne interference signal caused by the ADC is the main noise affecting the phase measurement performance and must be suppressed. This paper proposes a sampling timing jitter noise suppression system (STJNSS), which can set system parameters for high-frequency signals used for inter-satellite clock noise transmission, the system clock of the phasemeter, and the pilot frequency for suppressing ADC sampling timing jitter noise, meeting the needs of the current major space gravitational wave detection plans. The experimental results after the integration of SJNSS and the phase meter show that the phase measurement noise of the heterodyne interferometer signal reaches 2π μrad/Hz1/2@(0.1 mHz–1 Hz), which meets the requirements of space gravitational wave missions. Full article
(This article belongs to the Special Issue Deep Ultraviolet Detection Materials and Devices)
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17 pages, 4135 KiB  
Article
Temperature Estimation Method on Optic–Electric Composite Submarine Power Cable Based on Optical Fiber Distributed Sensing
by Chao Luo, Zhitao Feng, Yihua Zhu, Yuyan Liu, Yi Zhang, Ying Zhou, Muning Zhang and Lijuan Zhao
Photonics 2025, 12(6), 622; https://doi.org/10.3390/photonics12060622 - 19 Jun 2025
Viewed by 217
Abstract
The status of an optic–electric composite high-voltage submarine cable (referred to as submarine cable) can be monitored based on optical fiber-distributed sensing technology, and at the same time, no additional sensor is needed in the monitoring system. Currently, this technology is widely used [...] Read more.
The status of an optic–electric composite high-voltage submarine cable (referred to as submarine cable) can be monitored based on optical fiber-distributed sensing technology, and at the same time, no additional sensor is needed in the monitoring system. Currently, this technology is widely used in submarine cable monitoring systems. To estimate the temperatures of conductor and XLPE (cross-linked polyethylene) insulation of the submarine cable based on the ambient temperature and optical fiber temperature, the thermoelectric coupling field model of the 110 kV single-core submarine cable is established and validated. The thermoelectric coupling field models of the submarine cable with different values of ambient temperature and ampacity are built, and the influence of ambient temperature and ampacity on the temperatures of conductor, insulation and optical fiber is investigated. Furthermore, the relationship between the temperatures of the conductor and insulation and the ambient temperature and optical fiber temperature is obtained. Then, estimation formulas for temperatures of conductor and insulation of submarine cable according to ambient temperature and optical fiber temperature are obtained and preliminarily validated. This work lays the foundation for condition evaluation of the submarine cable insulation, life expectancy and maximum allowable ampacity estimation. Full article
(This article belongs to the Special Issue Advances in Optical Fiber Sensing Technology)
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16 pages, 3766 KiB  
Article
The Efficacy of Erbium-Ion, Diode, and CO2 Lasers in Debonding Attachments Used During Overlay Orthodontic Treatment and the Risk of Hard Tooth Tissue Damage Compared to Traditional Methods—An In Vitro Study
by Alina Florczak-Matyjek, Anna Nikodem, Julia Kensy, Jacek Matys and Kinga Grzech-Leśniak
Photonics 2025, 12(6), 621; https://doi.org/10.3390/photonics12060621 - 18 Jun 2025
Viewed by 306
Abstract
Objective: This in vitro study evaluated the effectiveness of three laser systems—diode, CO2, and Er:YAG—for debonding composite attachments used in aligner orthodontic therapy. Materials and Methods: Fifty extracted human premolars with composite attachments were divided into five groups (n = [...] Read more.
Objective: This in vitro study evaluated the effectiveness of three laser systems—diode, CO2, and Er:YAG—for debonding composite attachments used in aligner orthodontic therapy. Materials and Methods: Fifty extracted human premolars with composite attachments were divided into five groups (n = 10): control, RT (rotary tools), diode laser (980 nm, irradiance was 4811 W/cm2), CO2 laser (10.6 µm, irradiance 1531 W/cm2), and Er:YAG laser (2940 nm, irradiance 471.7 W/cm2). Shear bond strength (SBS) testing measured debonding forces. Enamel surface changes were evaluated using micro-CT, optical profilometry, and stereomicroscopy. The Adhesive Remnant Index (ARI) assessed residual bonding material. Results: Laser treatment increased enamel roughness (p < 0.05). Er:YAG laser caused the highest roughness (Sa = 2.03 µm) and up to 0.17 mm enamel loss but left minimal adhesive remnants and no fractures. Diode laser preserved surface smoothness with moderate bond weakening. CO2 laser had intermediate effects. RT showed the highest SBS but resulted in greater enamel alteration. SBS was significantly reduced in the laser groups, lowest for Er:YAG (81.7 ± 45.5 MPa vs. control 196.2 ± 75.3 MPa). ARI indicated better adhesive removal in the laser-treated groups, with Er:YAG showing the highest percentage of clean enamel surfaces (67% vs. 25%). Conclusions: Er:YAG demonstrated the best balance between effective debonding and enamel preservation. Diode and CO2 lasers also offer viable alternatives to rotary tools. Further clinical studies are recommended. Full article
(This article belongs to the Special Issue Photonics: 10th Anniversary)
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23 pages, 14051 KiB  
Article
A Novel Method for Water Surface Debris Detection Based on YOLOV8 with Polarization Interference Suppression
by Yi Chen, Honghui Lin, Lin Xiao, Maolin Zhang and Pingjun Zhang
Photonics 2025, 12(6), 620; https://doi.org/10.3390/photonics12060620 - 18 Jun 2025
Viewed by 259
Abstract
Aquatic floating debris detection is a key technological foundation for ecological monitoring and integrated water environment management. It holds substantial scientific and practical value in applications such as pollution source tracing, floating debris control, and maritime navigation safety. However, this field faces ongoing [...] Read more.
Aquatic floating debris detection is a key technological foundation for ecological monitoring and integrated water environment management. It holds substantial scientific and practical value in applications such as pollution source tracing, floating debris control, and maritime navigation safety. However, this field faces ongoing challenges due to water surface polarization. Reflections of polarized light produce intense glare, resulting in localized overexposure, detail loss, and geometric distortion in captured images. These optical artifacts severely impair the performance of conventional detection algorithms, increasing both false positives and missed detections. To overcome these imaging challenges in complex aquatic environments, we propose a novel YOLOv8-based detection framework with integrated polarized light suppression mechanisms. The framework consists of four key components: a fisheye distortion correction module, a polarization feature processing layer, a customized residual network with Squeeze-and-Excitation (SE) attention, and a cascaded pipeline for super-resolution reconstruction and deblurring. Additionally, we developed the PSF-IMG dataset (Polarized Surface Floats), which includes common floating debris types such as plastic bottles, bags, and foam boards. Extensive experiments demonstrate the network’s robustness in suppressing polarization artifacts and enhancing feature stability under dynamic optical conditions. Full article
(This article belongs to the Special Issue Advancements in Optical Measurement Techniques and Applications)
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12 pages, 3994 KiB  
Article
AI-Assisted Plasmonic Coupling Analysis of Spherical Gold Nanoparticles on Substrate
by Valeria D. Babaylova, Vladislav S. Tuchin, Nikita S. Petrov, Aleksey V. Kochakov, Anton A. Starovoytov, Igor A. Gladskikh and Daler R. Dadadzhanov
Photonics 2025, 12(6), 619; https://doi.org/10.3390/photonics12060619 - 18 Jun 2025
Viewed by 339
Abstract
A method of electrostatic deposition of CTAB-stabilized gold nanoparticles on a modified APTES and PSS surface was considered. Positively charged gold nanoparticles with a spherical shape were synthesized using a one-step synthesis method with a CTAB surfactant and deposited on a negatively charged [...] Read more.
A method of electrostatic deposition of CTAB-stabilized gold nanoparticles on a modified APTES and PSS surface was considered. Positively charged gold nanoparticles with a spherical shape were synthesized using a one-step synthesis method with a CTAB surfactant and deposited on a negatively charged modified glass substrate surface with an APTES/PSS layer. Depending on the concentration of the gold nanoparticles, the deposition time, and the modification of the substrate, both isolated nanoparticles with a narrow plasmon peak close to the maximum position in solution, and interacting nanoparticles with varying degrees of plasmonic coupling, were obtained. We also present a deep learning approach for rapid, non-contact estimation of relative plasmon coupling (PC) in gold nanoparticles deposited on substrates using simple camera images. To obtain the training dataset, gold nanoparticles were characterized by the intensity of peaks corresponding to plasmonic coupling in the long-wavelength region of the spectrum. A fully connected neural network was trained to regress PC values from color features, minimizing the mean-squared error. The best model, retrained on the full training set, achieved R2 = 0.83, RMSE = 0.007, MSE = 0.086, and MAE = 0.050 on the test dataset. Full article
(This article belongs to the Special Issue Advancements in Optical Metamaterials)
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14 pages, 2221 KiB  
Article
Design and Optimization of Broadband Optical Half-Band Filters Based on Cascaded MZIs
by Ke Zeng, Yu Zheng, Shu Liu, Xin Tang, Xinyu Ouyang, Keyi Fan and Chentong Yang
Photonics 2025, 12(6), 618; https://doi.org/10.3390/photonics12060618 - 18 Jun 2025
Viewed by 222
Abstract
In optical communication systems, optical half-band filters are essential for efficient spectral separation, necessitating stringent performance criteria such as a wide spectral range, low insertion loss, and minimal crosstalk. This paper proposes a broadband optical half-band filter based on a cascaded Mach–Zehnder Interferometer [...] Read more.
In optical communication systems, optical half-band filters are essential for efficient spectral separation, necessitating stringent performance criteria such as a wide spectral range, low insertion loss, and minimal crosstalk. This paper proposes a broadband optical half-band filter based on a cascaded Mach–Zehnder Interferometer (MZI) structure, which effectively improves spectral separation by enhancing flatness and sharpness at transition edges through the optimization of delay line length differences and phase compensation values. The results demonstrate that the proposed design achieves an insertion loss below 0.45 dB and inter-band crosstalk under −20.7 dB over a 40 nm bandwidth, with a roll-off of 2.2 dB/nm between 1517 nm and 1528 nm. The findings highlight the technical advantages of cascaded MZI structures in achieving high-precision spectral separation, offering a valuable reference for the development of future high-performance optical communication networks and integrated optical devices. Full article
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11 pages, 7053 KiB  
Article
Advances in Optical Metrology: High-Bandwidth Digital Holography for Transparent Objects Analysis
by Manoj Kumar, Lavlesh Pensia, Karmjit Kaur, Raj Kumar, Yasuhiro Awatsuji and Osamu Matoba
Photonics 2025, 12(6), 617; https://doi.org/10.3390/photonics12060617 - 18 Jun 2025
Viewed by 361
Abstract
Accurate and non-invasive optical metrology of transparent objects is essential in several commercial and research applications, from fluid dynamics to biomedical imaging. In this work, a digital holography approach for thickness measurement of glass plate and temperature mapping of candle flame is presented [...] Read more.
Accurate and non-invasive optical metrology of transparent objects is essential in several commercial and research applications, from fluid dynamics to biomedical imaging. In this work, a digital holography approach for thickness measurement of glass plate and temperature mapping of candle flame is presented that leverages a double-field-of-view (FOV) configuration combined with high spatial bandwidth utilization (SBU). By capturing a multiplexed hologram from two distinct objects in a single shot, the system overcomes the limitations inherent to single-view holography, enabling more comprehensive object information of thickness measurement and temperature-induced refractive index variations. The method integrates double-FOV digital holography with high SBU, allowing for accurate surface profiling and mapping of complex optical path length changes caused by temperature gradients. The technique exhibits strong potential for applications in the glass industry and microfluidic thermometry, convection analysis, and combustion diagnostics, where precise thermal field measurements are crucial. This study introduces an efficient holographic framework that advances the capabilities of non-contact measurement applications by integrating double-FOV acquisition into a single shot with enhanced spatial bandwidth exploitation. The approach sets the groundwork for real-time, volumetric thermal imaging and expands the applicability of digital holography in both research and industrial settings. Full article
(This article belongs to the Special Issue Optical Imaging Innovations and Applications)
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18 pages, 3589 KiB  
Article
Detection of Phosphorus in Water by Laser-Induced Breakdown Spectroscopy Based on Liquid-Solid Transformation of Graphite Substrate Combined with PLS-SVR Fusion Quantitative Analysis Algorithm
by Huijie Zhang, Yao Chen, Zongjie Bi, Xiaohua Che and Zhaoshuo Tian
Photonics 2025, 12(6), 616; https://doi.org/10.3390/photonics12060616 - 16 Jun 2025
Viewed by 227
Abstract
To enhance sensitivity in detecting phosphorus in water via laser-induced breakdown spectroscopy (LIBS), this study integrates liquid–solid conversion on graphite substrates with a PLS-SVR fusion algorithm. Optimized laser parameters (500 mJ, 13 pulses) improved plasma excitation and signal-to-noise ratios. The graphite substrate adsorbed [...] Read more.
To enhance sensitivity in detecting phosphorus in water via laser-induced breakdown spectroscopy (LIBS), this study integrates liquid–solid conversion on graphite substrates with a PLS-SVR fusion algorithm. Optimized laser parameters (500 mJ, 13 pulses) improved plasma excitation and signal-to-noise ratios. The graphite substrate adsorbed phosphorus, converting liquid samples into a solid matrix to suppress matrix interference and intensify spectral lines (P I 213.6 nm and 214.9 nm), achieving detection limits of 0.09 mg/L and 0.23 mg/L, respectively. Calibration curves showed high accuracy (R2 = 0.9936). In real-world testing, absolute errors were below 0.017 mg/L, with relative errors <12%, aligning closely with traditional ammonium molybdate spectrophotometry. The PLS-SVR algorithm boosted prediction accuracy through data enhancement and spectral feature extraction, reducing errors to 2.1% (0.625 mg/L) and 5.6% (2.5 mg/L). With rapid sample preparation (<10 min), this method offers an efficient, low-cost solution for in situ phosphorus monitoring, advancing LIBS from lab to field use and supporting precise eutrophication management. Full article
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31 pages, 2298 KiB  
Review
Optical Fiber-Based Structural Health Monitoring: Advancements, Applications, and Integration with Artificial Intelligence for Civil and Urban Infrastructure
by Nikita V. Golovastikov, Nikolay L. Kazanskiy and Svetlana N. Khonina
Photonics 2025, 12(6), 615; https://doi.org/10.3390/photonics12060615 - 16 Jun 2025
Viewed by 688
Abstract
Structural health monitoring (SHM) plays a vital role in ensuring the safety, durability, and performance of civil infrastructure. This review delves into the significant advancements in optical fiber sensor (OFS) technologies such as Fiber Bragg Gratings, Distributed Temperature Sensing, and Brillouin-based systems, which [...] Read more.
Structural health monitoring (SHM) plays a vital role in ensuring the safety, durability, and performance of civil infrastructure. This review delves into the significant advancements in optical fiber sensor (OFS) technologies such as Fiber Bragg Gratings, Distributed Temperature Sensing, and Brillouin-based systems, which have emerged as powerful tools for enhancing SHM capabilities. Offering high sensitivity, resistance to electromagnetic interference, and real-time distributed monitoring, these sensors present a superior alternative to conventional methods. This paper also explores the integration of OFSs with Artificial Intelligence (AI), which enables automated damage detection, intelligent data analysis, and predictive maintenance. Through case studies across key infrastructure domains, including bridges, tunnels, high-rise buildings, pipelines, and offshore structures, the review demonstrates the adaptability and scalability of these sensor systems. Moreover, the role of SHM is examined within the broader context of civil and urban infrastructure, where IoT connectivity, AI-driven analytics, and big data platforms converge to create intelligent and responsive infrastructure. While challenges remain, such as installation complexity, calibration issues, and cost, ongoing innovation in hybrid sensor networks, low-power systems, and edge computing points to a promising future. This paper offers a comprehensive amalgamation of current progress and future directions, outlining a strategic path for next-generation SHM in resilient urban environments. Full article
(This article belongs to the Special Issue Science and Applications of Optical Fiber Sensors: Recent Advances and Future Trends)
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19 pages, 2372 KiB  
Review
Frontier Advances and Challenges of High-Power Thulium-Doped Fiber Lasers in Minimally Invasive Medicine
by Wen-Yue Xu, Gong Wang, Yun-Fei Li, Yu Yu, Yulei Wang and Zhiwei Lu
Photonics 2025, 12(6), 614; https://doi.org/10.3390/photonics12060614 - 16 Jun 2025
Viewed by 529
Abstract
Lasers are increasingly used in the biomedical field because of their concentrated energy, good stability, ease of use, and other advantages, promoting the development of precision medicine to a higher level. Medical laser equipment has transformed from a single therapeutic tool in an [...] Read more.
Lasers are increasingly used in the biomedical field because of their concentrated energy, good stability, ease of use, and other advantages, promoting the development of precision medicine to a higher level. Medical laser equipment has transformed from a single therapeutic tool in an intelligent and precise diagnostic system. Existing clinical laser equipment has significant technical bottlenecks regarding soft-tissue ablation precision and multimodal diagnostic compatibility, which seriously restricts its clinical application. High-power thulium-doped fiber lasers with operating wavelengths of 1.9–2.1 μm provide a revolutionary solution for minimally invasive surgery due to their high compatibility with the absorption peaks of water molecules in biological tissues. This study reviews recent advances in high-power thulium-doped fiber lasers for minimally invasive therapies in the biomedical field. Breakthrough results in four major clinical application scenarios, namely, urological lithotripsy, tumor precision ablation, disfiguring dermatological treatment, and minimally invasive endovenous laser ablation, are also summarized. By systematically evaluating its potential for multimodal diagnostic and therapeutic applications and thoroughly exploring the technical challenges and strategies for clinical transformation, we aim to provide a theoretical basis and practical guidance for the clinical transformation and industrialization of new-generation medical laser technology. Full article
(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)
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11 pages, 3520 KiB  
Communication
Diode-End-Pumped Continuous-Wave Tunable Nd3+:LiYF4 Laser Operating on the 4F3/2→4I13/2 Transition
by Chu Chu, Shuang Wang, Xinhua Fu and Zhenhua Du
Photonics 2025, 12(6), 613; https://doi.org/10.3390/photonics12060613 - 14 Jun 2025
Viewed by 264
Abstract
A laser diode (LD) end-pumped continuous-wave (CW) tunable Nd3+:LiYF4 (Nd:YLF) laser operating on the 4F3/2→4I13/2 transition was performed. Four single-wavelength (SW) lasing at 1321, 1314, 1371, and 1364 nm in the π-polarized direction and [...] Read more.
A laser diode (LD) end-pumped continuous-wave (CW) tunable Nd3+:LiYF4 (Nd:YLF) laser operating on the 4F3/2→4I13/2 transition was performed. Four single-wavelength (SW) lasing at 1321, 1314, 1371, and 1364 nm in the π-polarized direction and three SW lasing at 1314, 1326, and 1371 nm in the σ-polarized direction were achieved using a tuning prism. At 20 W pump power, the σ-polarized 1314 nm emission generated 7.3 W power output with 39.4% slope efficiency. Further, the three-pair of switchable π-polarized dual-wavelengths (DWs) at 1321/1314 nm, 1371/1364 nm, and 1321/1364 nm and the two-pair of switchable σ-polarized DWs at 1314/1326 nm and 1314/1371 nm were also realized by rotating an intracavity birefringence filter (BF). In addition, by employing dual intracavity BFs, the balanced DW output power was attained, achieving 6.4 W total maximum output at 1314/1321 nm in the π-polarized direction. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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20 pages, 719 KiB  
Article
Entanglement Dynamics of Two Giant Atoms Embedded in a One-Dimensional Photonic Lattice with a Synthetic Gauge Field
by Vassilios Yannopapas
Photonics 2025, 12(6), 612; https://doi.org/10.3390/photonics12060612 - 14 Jun 2025
Viewed by 437
Abstract
We investigate the entanglement dynamics of two giant atoms coupled to a one-dimensional photonic lattice with synthetic chirality. The atoms are connected to multiple lattice sites in a braided configuration and interact with a structured photonic reservoir featuring direction-dependent hopping phases. By tuning [...] Read more.
We investigate the entanglement dynamics of two giant atoms coupled to a one-dimensional photonic lattice with synthetic chirality. The atoms are connected to multiple lattice sites in a braided configuration and interact with a structured photonic reservoir featuring direction-dependent hopping phases. By tuning the atomic detuning and the synthetic gauge phase, we identify distinct dynamical regimes characterized by decoherence-free population exchange, damped oscillations, long-lived revivals, and excitation trapping. Using a combination of time-domain simulations and resolvent-based analysis, we show how interference and band structure effects lead to the emergence of bound states, quasi-bound states, and phase-dependent entanglement dynamics. We compare the initial states with localized and delocalized atomic excitations, demonstrating that pre-existing entanglement can enhance the robustness against decoherence or accelerate its loss, depending on the system parameters. These results highlight the utility of synthetic photonic lattices and nonlocal emitter configurations in tailoring quantum coherence, entanglement, and information flows in structured environments. Full article
(This article belongs to the Special Issue Advanced Research in Quantum Optics)
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23 pages, 890 KiB  
Review
Space–Time Duality in Optics: Its Origin and Applications
by Govind P. Agrawal
Photonics 2025, 12(6), 611; https://doi.org/10.3390/photonics12060611 - 13 Jun 2025
Viewed by 306
Abstract
The concept of space–time duality in optics was originally based on the mathematical connection between the diffraction of beams in space and the dispersion of pulses in time. This concept has been extended in recent years from the temporal analog of reflection for [...] Read more.
The concept of space–time duality in optics was originally based on the mathematical connection between the diffraction of beams in space and the dispersion of pulses in time. This concept has been extended in recent years from the temporal analog of reflection for optical pulses to photonic time crystals in a medium where refractive index varies with time in a periodic fashion. In this review, I discuss how the concept of space–time duality and the use of nonlinear optics has led to many advances in recent years. Starting from the historical origin of space–time duality, time lenses and their applications are reviewed first. Later sections cover phenomena such as soliton-induced temporal reflection, time-domain waveguiding, and the formation of spatiotemporal Bragg gratings. Full article
(This article belongs to the Special Issue Recent Advances in Nonlinear Optics: From Fundamentals to Applications)
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11 pages, 1840 KiB  
Article
Passively Mode-Locked Tm:YAP Laser Utilizing a Mo2TiAlC2 MAX Phase Saturable Absorber for Modulation
by Chen Wang, Tianjie Chen, Zhe Meng, Sujian Niu, Zhaoxue Li and Xining Yang
Photonics 2025, 12(6), 610; https://doi.org/10.3390/photonics12060610 - 13 Jun 2025
Viewed by 249
Abstract
This study reports a novel MAX phase material, Mo2TiAlC2, as a passively mode-locking (PML) saturable absorber (SA) for a Tm:YAP laser operating in the 2 μm wavelength range. The systematic characterization of its nonlinear optical properties was quantitatively analyzed [...] Read more.
This study reports a novel MAX phase material, Mo2TiAlC2, as a passively mode-locking (PML) saturable absorber (SA) for a Tm:YAP laser operating in the 2 μm wavelength range. The systematic characterization of its nonlinear optical properties was quantitatively analyzed using I-scan methodology, demonstrating a significant modulation depth of 3.5%, which indicated strong nonlinear optical activity. Within the realm of optimal cavity conditions, a remarkable performance by the PML configuration can be discerned. A stable pulsed emission was manifested at 1937 nm, wherein an average output power reaching 620 mW was achieved. A pulse temporal span of 989.5 ps was acquired with a corresponding repetition frequency of 103.1 MHz, indicating robust mode-locked synchronization. Notably, the beam quality factors (M2) along the orthogonal spatial axes were observed with values measuring 1.12 and 1.18, respectively, indicating propagation characteristics close to those of diffraction-limited beams. Full article
(This article belongs to the Special Issue Advances in Ultrafast Laser Science and Applications)
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8 pages, 1476 KiB  
Communication
Characterization of a Wide-Band Single-Photon Detector Based on Transition-Edge Sensor
by Jingkai Xia, Shuo Zhang and Bingjun Wu
Photonics 2025, 12(6), 609; https://doi.org/10.3390/photonics12060609 - 13 Jun 2025
Viewed by 422
Abstract
A superconducting transition-edge sensor (TES) as a microcalorimeter detects incoming photons by measuring heat converted from photon energy. With high resolving power and low noise levels, a TES is sensitive to single photons and able to count photons within a wide spectral band [...] Read more.
A superconducting transition-edge sensor (TES) as a microcalorimeter detects incoming photons by measuring heat converted from photon energy. With high resolving power and low noise levels, a TES is sensitive to single photons and able to count photons within a wide spectral band from X-ray to near-infrared. We have developed a TES detector aiming at soft X-ray spectroscopy applications. In this work, the performance of this detector is characterized. It is shown that the energy resolution of this detector is about 1.8 eV for 1.5 keV photons. The good resolution is also kept in visible range, enabling photon-number resolving for 405 nm photons. Full article
(This article belongs to the Special Issue Recent Progress in Single-Photon Generation and Detection)
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13 pages, 2468 KiB  
Article
On-Chip Silicon Bragg-Grating-Waveguide-Based Polymer Slot for Gas Sensing
by Merna Khafagy, Maira Khafagy, Passant Hesham and Mohamed A. Swillam
Photonics 2025, 12(6), 608; https://doi.org/10.3390/photonics12060608 - 12 Jun 2025
Viewed by 851
Abstract
This work presents a novel CO2 gas sensor based on a slotted polymer-phaseshift Bragg grating (SP-PSBG) waveguide filled with polyhexamethylene biguanide (PHMB) as the sensing medium. The transmission resonance, characterized by a narrow peak with a full width at half maximum [...] Read more.
This work presents a novel CO2 gas sensor based on a slotted polymer-phaseshift Bragg grating (SP-PSBG) waveguide filled with polyhexamethylene biguanide (PHMB) as the sensing medium. The transmission resonance, characterized by a narrow peak with a full width at half maximum (FWHM) of 1.6 nm within the Bragg grating bandgap, is highly responsive to refractive index changes in PHMB caused by variations in CO2 concentration. Numerical simulations demonstrate a sensitivity of 14.4 pm/ppm, outperforming conventional gas sensors based on functional material coatings. This enhanced performance comes from the direct interaction between the PHMB-filled resonant structure and the cladding that contains CO2 molecules, eliminating the need for polymer-coated cladding layers. The optimization approach employed in this design focuses on maximizing the optical confinement factor within the PHMB-filled slot, leading to an effective overlap between the guided optical mode and the sensing material. Full article
(This article belongs to the Special Issue Advances in Integrated Photonics)
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15 pages, 4420 KiB  
Article
Single-Pixel Imaging Reconstruction Network with Hybrid Attention and Enhanced U-Net
by Bingrui Xiao, Huibin Wang and Yang Bu
Photonics 2025, 12(6), 607; https://doi.org/10.3390/photonics12060607 - 12 Jun 2025
Viewed by 651
Abstract
Single-pixel imaging has the characteristics of a simple structure and low cost, which means it has potential applications in many fields. This paper proposes an image reconstruction method for single-pixel imaging (SPI) based on deep learning. This method takes the Generative Adversarial Network [...] Read more.
Single-pixel imaging has the characteristics of a simple structure and low cost, which means it has potential applications in many fields. This paper proposes an image reconstruction method for single-pixel imaging (SPI) based on deep learning. This method takes the Generative Adversarial Network (GAN) as the basic architecture, combines the dense residual structure and the deep separable attention mechanism, and reduces the parameters while ensuring the diversity of feature extraction. It also reduces the amount of computation and improves the computational efficiency. In addition, dual-skip connections between the encoder and decoder parts are used to combine the original detailed information with the overall information processed by the network structure. This approach enables a more comprehensive and efficient reconstruction of the target image. Both simulations and experiments have confirmed that the proposed method can effectively reconstruct images at low sampling rates and also achieve good reconstruction results on natural images not seen during training, demonstrating a strong generalization capability. Full article
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14 pages, 1912 KiB  
Article
Optical Properties of Near-Infrared Phosphor and Its Application in the Fabrication of Broadband Wavelength Emitters
by Thi-Hanh-Thu Vu, Trong-Nam Tran and Quang-Khoi Nguyen
Photonics 2025, 12(6), 606; https://doi.org/10.3390/photonics12060606 - 12 Jun 2025
Viewed by 623
Abstract
Herein, we study a method for developing a broad-emission emitter that can emit radiation from the visible light to NIR regions. Firstly, an NIR phosphor’s optical properties (e.g., scattering vs. weight concentration, conversion efficiency, and emission spectra under blue and red light excitation) [...] Read more.
Herein, we study a method for developing a broad-emission emitter that can emit radiation from the visible light to NIR regions. Firstly, an NIR phosphor’s optical properties (e.g., scattering vs. weight concentration, conversion efficiency, and emission spectra under blue and red light excitation) are investigated. Then, pcW-LEDs encapsulated with NIR down-conversion phosphor samples are prepared to test these optical properties. The results show that pcW-LEDs encapsulated with the NIR phosphor at different weight concentrations of 10.0%, 12.5%, and 15.5%, respectively, emit a broadband emission from 400 nm to 900 nm. The EQE values of the pcW-LEDs encapsulated with NIR phosphor at weight concentrations of 10%, 12.5%, and 15.0% are 26%, 23%, and 19%, respectively. The correlated color temperatures of these samples are 5767 K, 5940 K, and 6068 K, respectively. The obtained radiant fluxes of the samples are 26 mW, 22 mW, and 18 mW, respectively, at an injection current of 50 mA. Full article
(This article belongs to the Special Issue Innovative Optical Technologies in Advanced Manufacturing)
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12 pages, 2567 KiB  
Article
High-Power 650 nm Dense Spectral Beam Combining System Based on a Compression Telescope and Imaging Module
by Bingxu Zhao, Lingqian Meng, Man Hu, Xuyan Zhou, Jing Liu, Nihui Zhang, Aiyi Qi, Fu Ting, Weiqiao Zhang, Ao Chen and Wanhua Zheng
Photonics 2025, 12(6), 605; https://doi.org/10.3390/photonics12060605 - 12 Jun 2025
Viewed by 462
Abstract
In this thesis, a 650 nm dense spectral beam combining (DSBC) system based on a compression telescope module (CM) and an imaging module (IM) is proposed (CM&IM DSBC system). Based on twenty-two (22) 650 nm COS (Chip on Submount) single-emitters, the system successfully [...] Read more.
In this thesis, a 650 nm dense spectral beam combining (DSBC) system based on a compression telescope module (CM) and an imaging module (IM) is proposed (CM&IM DSBC system). Based on twenty-two (22) 650 nm COS (Chip on Submount) single-emitters, the system successfully achieves the first high-power and non-crosstalk beam combining output in the visible red band, with a maximum beam output power of 29.984 W. Compared with the 650 nm traditional DSBC system we proposed last year, the system solves both the crosstalk problem due to its larger optical path and the beam combining power drop caused by the direct reduction in the optical path. The final output power and DSBC efficiency are improved by more than 53% and 10%, respectively. The final beam brightness is improved by nearly 30%. Compared to a COS single-emitter, the brightness increase is more than 22 times. This achievement provides a new idea for the subsequent experimental research and product development of higher-power visible red-light band DSBC systems that can be applied in the industrial field. Full article
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15 pages, 3300 KiB  
Review
Structural Health Monitoring by Fiber Optic Sensors
by Alfredo Guemes, Luis Eduardo Mujica, Daniel del-Río-Velilla and Antonio Fernandez-Lopez
Photonics 2025, 12(6), 604; https://doi.org/10.3390/photonics12060604 - 12 Jun 2025
Viewed by 618
Abstract
Although a crack creates a significant strain field at its tip, its effect on the strain field becomes nearly negligible only a few centimeters away from the crack, which complicates the task of damage detection. Two approaches are currently in use. The first [...] Read more.
Although a crack creates a significant strain field at its tip, its effect on the strain field becomes nearly negligible only a few centimeters away from the crack, which complicates the task of damage detection. Two approaches are currently in use. The first one is a local approach that can detect damage if it intersects the optical fiber path; it is straightforward to implement but is limited to cases where the potential damage location can be anticipated (for example, in a concrete beam under flexural loads or around aircraft cargo doors). The second one, a global approach, seeks to identify damage anywhere in the structure by detecting subtle changes in the field of global strain. There is a need for algorithms to compare the strain dataset before and after damage. Machine learning offers tools to achieve this, but these tools have to be carefully selected to achieve good damage detectability. In this paper, we compare algorithms based on multivariate data analysis as well as data processing using neural networks, comparing their performance on a real structure. Full article
(This article belongs to the Special Issue Advances in Optical Fiber Sensing Technology)
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12 pages, 5133 KiB  
Article
Exploring the Impact of Inlet Velocity Distribution on the Thermal Performance of a Laser Rod in a Diode Side-Pumped Amplifier
by Shuzhen Nie, Jinglan Lin, Tianzhuo Zhao and Xiaolong Liu
Photonics 2025, 12(6), 603; https://doi.org/10.3390/photonics12060603 - 12 Jun 2025
Viewed by 574
Abstract
Research on the thermal analysis of laser diode (LD) side-pumped amplifiers is a critical step in the design of high-power solid-state laser systems. Instead of adopting a standard solid modeling approach that only considers a laser rod, a fluid–structure interaction model is employed [...] Read more.
Research on the thermal analysis of laser diode (LD) side-pumped amplifiers is a critical step in the design of high-power solid-state laser systems. Instead of adopting a standard solid modeling approach that only considers a laser rod, a fluid–structure interaction model is employed for analysis using the FLUENT 2021 R1 software. This model integrates the cooling structure, coolant, and laser rod, incorporating their relevant material parameters. By considering both uniform and non-uniform inlet velocity distributions as loading conditions, the study reveals remarkably different thermal simulation results. The correlation between thermal analysis outcomes and the total inlet flow rates is calculated, while temperature and stress distributions are obtained under a varying internal heat source. It was observed that the non-uniform inlet velocity distribution has little impact on the rod’s maximum temperature but significantly influences the maximum equivalent stress. This finding underscores the necessity of accounting for non-uniform inlet distributions during the design of laser amplifiers to achieve more accurate thermal simulation results and optimize structural reliability. Full article
(This article belongs to the Special Issue Advances in Solid-State Laser Technology and Applications)
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10 pages, 2369 KiB  
Article
Ultra-Compact Mach–Zehnder Refractometer Based on Rice-Shaped Air Cavity Beam Expansion
by Zonghao Mu, Tian Tian, Yiwei Ma, Song Li and Tao Geng
Photonics 2025, 12(6), 602; https://doi.org/10.3390/photonics12060602 - 12 Jun 2025
Viewed by 479
Abstract
This paper reports and demonstrates, for the first time, a Mach–Zehnder interferometer (MZI) sensor for refractive index (RI) detection based on a rice-shaped air cavity (RAC). In this design, RACs are inserted on both sides of a no-core fiber (NCF), functioning as a [...] Read more.
This paper reports and demonstrates, for the first time, a Mach–Zehnder interferometer (MZI) sensor for refractive index (RI) detection based on a rice-shaped air cavity (RAC). In this design, RACs are inserted on both sides of a no-core fiber (NCF), functioning as a beam expander and receiver. When the input light enters the NCF through the RAC, it is fully excited from the fundamental mode to higher-order modes within just 500 μm of propagation. This enables the sensor to achieve exceptionally high sensitivity in external RI detection. By adjusting the width of the RAC, the RI sensitivity can be effectively tuned. When the RAC measures 30.6 × 70 μm, the two selected transmission peaks reach maximum RI sensitivities of 1550.41 nm/RIU and 1810.89 nm/RIU, respectively. Notably, the total length of the sensor is only 0.64 mm, offering a promising approach for the development of ultra-compact RI sensors in the future. Full article
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14 pages, 6581 KiB  
Article
High-Precision Diagnosis of the Whole Process of Laser-Induced Plasma and Shock Waves Using Simultaneous Phase-Shift Interferometry
by Lou Gao, Hongchao Zhang, Jian Lu and Zhonghua Shen
Photonics 2025, 12(6), 601; https://doi.org/10.3390/photonics12060601 - 11 Jun 2025
Viewed by 685
Abstract
This study employs the simultaneous phase-shift interferometry (SPSI) system to diagnose laser-induced plasma (LIP) and shock wave (SW). In high-density LIP diagnostics, the Faraday rotation effect causes probe light polarization deflection, rendering traditional fixed-phase-demodulation methods ineffective, the Carré phase-recovery algorithm is adopted and [...] Read more.
This study employs the simultaneous phase-shift interferometry (SPSI) system to diagnose laser-induced plasma (LIP) and shock wave (SW). In high-density LIP diagnostics, the Faraday rotation effect causes probe light polarization deflection, rendering traditional fixed-phase-demodulation methods ineffective, the Carré phase-recovery algorithm is adopted and its applicability is verified. Uncertainty analysis and precision verification show that the total phase shift uncertainty is controlled within 0.045 radians, equivalent to a refractive index accuracy of 8.55×10−6, with sensitivity to weak perturbations improved by approximately one order of magnitude compared to conventional carrier-frequency interferometry. Experimental results demonstrate that the SPSI system precisely captures the initial spatiotemporal evolution of LIP and tracks shock waves at varying attenuation levels, exhibiting notable advantages in weak shock wave detection. This research validates the SPSI system’s high sensitivity to transient weak perturbations, offering a valuable diagnostic tool for high-vacuum plasmas, low-pressure shock waves, and stress waves in optical materials. Full article
(This article belongs to the Special Issue Advances in Laser Measurement)
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11 pages, 12416 KiB  
Article
Automated Quantification and Statistical Characterization of 3D Morphological Parameters of Red Blood Cells and Blood Coagulation Structures Using Flow Cytometry with Digital Holographic Microscopy
by Hideki Funamizu
Photonics 2025, 12(6), 600; https://doi.org/10.3390/photonics12060600 - 11 Jun 2025
Viewed by 706
Abstract
Label-free, high-throughput, and 3D morphological analysis of blood cells remains a major challenge in biomedical optics. In this study, we investigate this issue using flow cytometry with digital holographic microscopy (DHM) to enable real-time, label-free imaging of red blood cells (RBCs) and blood [...] Read more.
Label-free, high-throughput, and 3D morphological analysis of blood cells remains a major challenge in biomedical optics. In this study, we investigate this issue using flow cytometry with digital holographic microscopy (DHM) to enable real-time, label-free imaging of red blood cells (RBCs) and blood coagulation structures (BCSs) without the need for staining or chemical pretreatment. We demonstrate an approach for the automated quantification and statistical characterization of these cells using quantitative phase information reconstructed from digital holograms. Although established image processing techniques such as phase unwrapping and segmentation are used, this study presents, to the best of our knowledge, the first statistical characterization of the 3D morphological features of BCSs. This is particularly useful in analyzing the heterogeneous and complex 3D structures of BCSs, which are difficult to assess using conventional microscopy. The results suggest that this DHM-based flow cytometry system provides a promising platform for non-invasive, real-time morphological evaluation of blood samples and has potential applications in hematological diagnostics and research related to blood coagulation. Full article
(This article belongs to the Special Issue Optical Imaging and Measurements: 2nd Edition)
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31 pages, 12794 KiB  
Article
Enhanced Defect Detection in Additive Manufacturing via Virtual Polarization Filtering and Deep Learning Optimization
by Xu Su, Xing Peng, Xingyu Zhou, Hongbing Cao, Chong Shan, Shiqing Li, Shuo Qiao and Feng Shi
Photonics 2025, 12(6), 599; https://doi.org/10.3390/photonics12060599 - 11 Jun 2025
Viewed by 1292
Abstract
Additive manufacturing (AM) is widely used in industries such as aerospace, medical, and automotive. Within this domain, defect detection technology has emerged as a critical area of research focus in the quality inspection phase of AM. The main challenge lies in that under [...] Read more.
Additive manufacturing (AM) is widely used in industries such as aerospace, medical, and automotive. Within this domain, defect detection technology has emerged as a critical area of research focus in the quality inspection phase of AM. The main challenge lies in that under extreme lighting conditions, strong reflected light obscures defect feature information, leading to a significant decrease in the defect detection rate. This paper introduces a novel methodology for intelligent defect detection in AM components with reflective surfaces, leveraging virtual polarization filtering (IEVPF) and an improved YOLO V5-W model. The IEVPF algorithm is designed to enhance image quality through the virtual manipulation of light polarization, thereby improving defect visibility. The YOLO V5-W model, integrated with CBAM attention, DenseNet connections, and an EIoU loss function, demonstrates superior performance in defect identification across various lighting conditions. Experiments show a 40.3% reduction in loss, a 10.8% improvement in precision, a 10.3% improvement in recall, and a 13.7% improvement in mAP compared to the original YOLO V5 model. Our findings highlight the potential of combining virtual polarization filtering with advanced deep learning models for enhanced AM surface defect detection. Full article
(This article belongs to the Special Issue Advances in Micro-Nano Optical Manufacturing)
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15 pages, 2860 KiB  
Article
Self-Assembly of Zinc Oxide Photonic Crystals in Viscous Liquids: Synthesis, Characterization, and Application to Colored Contact Lenses
by Shuwen Hou, Zichen Pan, Lin Zhao, Xue-Lian Han, Quan-Xi Zhang and Shou-Nian Ding
Photonics 2025, 12(6), 598; https://doi.org/10.3390/photonics12060598 - 11 Jun 2025
Viewed by 459
Abstract
Structural color is a kind of natural color that widely exists in nature. The ordered microstructure of nano materials can absorb or reflect light of specific wavelength, thus showing colorful colors. Structural color is an ideal choice for color contact lens pattern pigment [...] Read more.
Structural color is a kind of natural color that widely exists in nature. The ordered microstructure of nano materials can absorb or reflect light of specific wavelength, thus showing colorful colors. Structural color is an ideal choice for color contact lens pattern pigment due to its good tinting degree, stability, and nontoxicity. This paper explores a method for synthesis of zinc oxide (ZnO) nanoparticles with a high refractive index and enhancement of the brightness of the structured colors by introducing carbon black nanoparticles. This method is convenient and successful to prepare ZnO ink, which can produce bright structural colors, and to produce color patterns through rubber pad printing. It is worth mentioning that ZnO nanoparticles can be self-assembled and arranged in contact lens ink without subsequent complicated processing. At the same time, the color only comes from ZnO and carbon black. While there is no other organic matter, the presence of nanoparticles plays a certain role in sterilization. Blue contact lenses prepared by this method have bright structural color, high oxygen permeability, and high hydrophilicity. At the same time, a cell viability test showed that the contact lenses prepared by this method had low adsorption capacity for lipids and proteins, reflecting the photonic crystal’s high biocompatibility. In summary, a trend for future research is to use high-refractive-index zinc oxide nanoparticles to produce structural colors rather than employing conventional contact lens pigments. Full article
(This article belongs to the Special Issue Emerging Trends in Photonic Crystals)
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12 pages, 1949 KiB  
Article
Phonon Structure Engineering for Intrinsically Spectrally Selective Emitters by Anion Groups
by Rui Zhang, Enhui Huang, Wenying Zhong and Bo Xu
Photonics 2025, 12(6), 597; https://doi.org/10.3390/photonics12060597 - 11 Jun 2025
Viewed by 767
Abstract
Spectrally selective emitters (SSEs) have attracted considerable attention, because of radiative cooling, which could dissipate the heat from earth to outer space through the atmospheric window without any energy input. Intrinsically inorganic SSEs have significant advantages to other SSEs, such as the low [...] Read more.
Spectrally selective emitters (SSEs) have attracted considerable attention, because of radiative cooling, which could dissipate the heat from earth to outer space through the atmospheric window without any energy input. Intrinsically inorganic SSEs have significant advantages to other SSEs, such as the low fabrication cost due to the extremely simple structures and long life span under solar exposure. However, few inorganic materials can act as intrinsic SSEs due to the limited emissions in the atmospheric window. Here, we propose a strategy to design intrinsic SSEs by complementing the IR-active phonons in atmospheric window with anion groups. Accordingly, we demonstrate borates containing both [BO3]3− and [BO4]5− units can exhibit high emissivity within the whole atmospheric window, because the IR-active phonons of [BO3]3− units usually locate around 8 and 13 μm, while those of [BO4]5− units distribute in 9~11 μm. Furthermore, K3B6O10Cl and BaAlBO4 are selected as two examples to display their near-unity emissivity (>95%) within the whole atmospheric window experimentally. These results not only offer a new strategy for the design of intrinsic SSEs, but also endow wide band-gap borates containing both [BO3]3− and [BO4]5− units with great potential applications for radiative cooling. Full article
(This article belongs to the Special Issue Infrared Optoelectronic Materials and Devices)
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24 pages, 3261 KiB  
Review
Some Insights on Kerr Lensing Effects
by Kamel Aït-Ameur and Abdelkrim Hasnaoui
Photonics 2025, 12(6), 596; https://doi.org/10.3390/photonics12060596 - 10 Jun 2025
Viewed by 1365
Abstract
The research on high-order transverse modes in lasers was largely abandoned a few years after the invention of the laser in 1960. The main reason for this was that high-order beams are more divergent and less bright than the Gaussian beam. In the [...] Read more.
The research on high-order transverse modes in lasers was largely abandoned a few years after the invention of the laser in 1960. The main reason for this was that high-order beams are more divergent and less bright than the Gaussian beam. In the present paper, we showed that the behaviour of LGp0 beams faced to the optical Kerr effect (OKE) varies considerably depending on the mode order (p = 0 or p≥1). We focused our attention on the properties of LG00 and LG10 beams when subject to OKE, and we found that the LG10 beam keeps its focusability much better than the LG00 beam. This property has at least two applications concerning first the conception of high-intensity laser chains not based on a Gaussian beam but on an LG10 beam and second, the use of an LG10 beam instead of the usual Gaussian beam which can reduce drastically the protection of optical limiters based on OKE; this constitutes a counter-measure against such limiters. Full article
(This article belongs to the Special Issue Advanced Methods in Exploring Light–Matter Interactions and Nonlinear Effects Optics Applications)
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18 pages, 2909 KiB  
Article
Characterization of a Supersonic Plasma Jet by Means of Optical Emission Spectroscopy
by Ruggero Barni, Hanaa Zaka, Dipak Pal, Irsa Amjad and Claudia Riccardi
Photonics 2025, 12(6), 595; https://doi.org/10.3390/photonics12060595 - 10 Jun 2025
Viewed by 821
Abstract
We discuss an innovative thin film deposition method, Plasma Assisted Supersonic Jet Deposition, which combines the chemistry richness of a reactive cold plasma environment and the assembly control of the film growth allowed by a supersonic jet directed at the substrate. Optical Emission [...] Read more.
We discuss an innovative thin film deposition method, Plasma Assisted Supersonic Jet Deposition, which combines the chemistry richness of a reactive cold plasma environment and the assembly control of the film growth allowed by a supersonic jet directed at the substrate. Optical Emission Spectroscopy was used to characterize the plasma state and the supersonic jet, together with its interaction with the substrate. We obtained several results in the deposition of silicon oxide thin films from Hexamethyldisiloxane, with different degrees of organic groups retention. In particular we exploited the features of emission spectra to measure the plasma dissociation and oxidation degree of the organic groups, as a function of the jet parameters. If controlled growth is achieved, such films are nanostructured materials suitable for applications like catalysis, photo catalysis, energy conversion and storage, besides their traditional uses as a barrier or protective coatings. Full article
(This article belongs to the Special Issue Steady-State and Ultrafast Time-Resolved Optical Spectroscopy and Laser Applications in Biology, Chemistry, Physics, Biomedical Optics and High-Resolution Imaging)
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