Search Results (222)

Conventional optical imaging struggles to acquire clear images of underwater scenes in turbid water. In this paper, a new dual-DMD single-pixel 3D imaging (DSP3DI) system is designed and constructed to realize the 3D shape reconstruction in highly turbid water conditions. Leveraging the spectral dependence of the scattering coefficient of water on wavelength, the designed system uses a 532 nm laser as the illumination source to minimize scattering and absorption losses during light propagation, and two digital micromirror devices (DMDs) are used to generate phase-shifting fringe patterns and sampling patterns, respectively, and then uses a single-pixel detector to sequentially collect the spatial light field reflected from the surface of the object. A single-pixel imaging (SPI) method based on a cake-cutting strategy for Hadamard encoding reconstructs the deformed fringe images, from which phase information is recovered to calculate the 3D shape of objects. The experimental results show that the system not only achieves millimeter-level measurement accuracy but also successfully reconstructs the 3D shape of complex objects at a sampling rate of 10% and in turbidities as high as 40 NTU. The proposed system, characterized by its compact structure, high measurement accuracy, and strong scattering resistance, offers a novel solution for high-precision 3D imaging in highly turbid water. Full article

Vertical-External-Cavity Surface-Emitting Lasers (VECSELs) have gained significant attention over the past two decades due to their versatility in a wide range of photonic applications. This review focuses on VECSEL configurations for dual-wavelength emission, highlighting their use in high-resolution spectroscopy, terahertz (THz) generation, and advanced optical communication. We explore recent developments in VECSEL designs, including systems utilizing birefringent crystals for polarization-based frequency separation and configurations with dual-VECSEL chips or dual-gain regions within a single cavity. These two-wavelength VECSELs enable diverse operation modes, including narrow-linewidth, pulsed, multimode, and frequency-converted emission, with high-brightness output, excellent beam quality, and tunable wavelengths. Additionally, the review discusses advancements in dual-frequency VECSELs, with applications in LIDAR systems for environmental monitoring, highly stable optical clocks, and fiber sensors. We examine improvements in cavity design, semiconductor structures, and power stabilization, which have enhanced frequency stability and spectral purity, making VECSELs suitable for precision metrology and sensing applications. Full article

Optical klystrons have been developed in storage ring free-electron lasers (FELs) as insertion devices to increase the FEL gain in a straight section with limited length. By adjusting the magnetic field in the dispersion section of the optical klystron to shift the relative delay between the electron bunch and FEL pulse from an integer multiple of the FEL wavelength, FELs can oscillate at two wavelengths. The electron density of the electron bunch that interacts with the FEL pulse in a small-signal regime is modulated at the FEL wavelength period. When the FEL oscillates simultaneously at two wavelengths, the electron density of the electron bunch beats through the modulation with two periods. This beat generates long-wavelength coherent edge radiation at a bending magnet located in the straight section containing the optical klystron. Difference-frequency waves induced by dual-wavelength ultraviolet free-electron lasers generate a high-intensity mid-infrared monochromatic beam. Our findings will lay the foundation for the development of the difference-frequency waves of soft X-rays and extreme ultraviolet light using hard X-ray FELs. Full article

This work presents an original implementation of the digital sampling pipeline for spaceborne Fourier Transform Spectrometers (FTSs). The implementation aims at improving the robustness of the spectrometer to harsh environmental conditions, including mechanical vibrations and a wide operational temperature range, avoiding the use of dedicated electronic hardware for the interferometer mirrors’ speed control and interferogram sampling. The FTS configuration is based on the constant time step sampling of the interferometer using a standard ADC (Analogue to Digital Converter), along with two metrology laser channels. The development tool is a MATLAB-based simulator developed to emulate the FTS and, in particular, the generation and acquisition of interferograms, incorporating harmonic vibrations and detector noise. The simulator was exploited to compare state-of-the-art techniques and newly implemented variants. An improvement of the arccosine method is first proposed, revising the normalisation process to exploit the full set of recorded data without discarding critical points. Subsequently, methods using two reference channels have been developed and evaluated. Two implementations are considered: two references at the same wavelength with an optimised phase shift (i.e., π/2) and two references at different wavelengths. Different data fusion strategies are compared in terms of spectral uncertainty, varying types of simulated disturbances and noise amplitudes. Results show that the optimal combination of two same-wavelength references consistently outperforms any other configuration, yielding lower average spectral errors and more stable performance over the frequency range and for a lower SNR of reference channels. Conversely, dual-wavelength strategies exhibit reduced accuracy, though they offer flexibility when fixed phase shifts cannot be maintained. The optimal combination of two same-wavelength reference channels, phase-shifted, is a promising configuration for spaceborne FTSs, so the development and test of an instrument breadboard is envisaged as the consequent development of this work. Full article

Background/Objectives: Photobiomodulation (PBMT) has been shown to improve tissue healing; however, the best protocol for different clinical challenges is not clearly determined. Despite the good previous outcomes of the PBMT in healing of the third molar surgical sites, the ideal protocol of PBMT was not determined. The objective of this split-mouth double-blinded randomized clinical trial was to compare the effect of photobiomodulation (PBMT) with red and infrared wavelengths combined and PBMT with only red wavelength on the healing of post-extraction alveoli of third molars. Methods: Twenty patients underwent third molar extraction. The alveoli were treated randomly in a split mouth model with: PBMT with red laser (R-PBMT) or PBMT with red and infrared laser combined (IR-R-PBMT). PBMT was applied immediately, and 3 and 7 days after surgery. Patients were clinically evaluated in relation to repair (bleeding, exudate, color, and consistency of the tissues), degree of the edema, and through the application of a VAS scale (pain, edema, bleeding, chewing, and mouth opening) in the baseline period, and 3, 7, 14, 30, and 90 days after the surgical procedure. In addition, bone tissue density and structure were measured by radiographic analysis at 7 and 90 days postoperatively. Results: Clinical analysis showed that IR-R-PBMT induce more reduction in the edema 7 days after surgery compared with the R-PBMT; however, no significant differences were noted between groups in other parameters. Conclusions: IR-R-PBMT reduces the edema after 7 days of third molar extraction compared with the R-PBMT. Registration: This study was registered with the Brazilian Registry of Clinical Trials (REBEC-RBR-103g7j28; date of registration 12 July 2023) under number U1111-1297-6962. Full article

In high-power laser systems, extrinsic impurities—particularly Ce introduced during conventional ring polishing—have been identified as critical contributors to the degradation of laser-induced damage resistance in fused silica optical components. This study systematically investigates the effects of cerium substitutional doping on the electronic structure and optical properties of fused silica, integrating first-principles density functional theory calculations with experimental characterizations. The results demonstrate that substitutional incorporation of cerium atoms into the fused silica framework introduces deep-level defect states within the band gap, resulting in band gap narrowing and absorption edge redshift of the material. The energy position of the defect states depends on the Ce doping configuration. Among them, the Ce-4f orbital constitutes the dominant component of the defect state’s electronic structure, while the neighboring atomic orbitals such as O-2p and Si-3s/3p participate in bonding through hybridization, thereby determining the depth and distribution characteristics of the defect levels. The optical absorption edge of cerium-doped fused silica undergoes a significant redshift from the intrinsic value of 222 nm to 468 nm in the dual-Ce adjacent-site doping configuration, thereby endowing the material with substantial optical absorption capability at a wavelength of 355 nm. μ-UVPL spectroscopy combined with μ-XRD and other characterization analyses confirmed that the characteristic emission peak at 450 nm on the surface region of fused silica originated from Ce-related defect centers; this spectral feature was consistent with the defect state electronic structure predicted by the diatomic nearest-neighbor doping model. LIDT tests further indicated that the Ce-contaminated area significantly weakened the material’s laser damage resistance under 355 nm laser irradiation. This study further explained the mechanism by which traditional polishing-induced Ce element doping causes the low laser damage threshold of fused silica optical components, providing a theoretical basis for improving their performance. Full article

A robust and cost-effective fiber-optic ultrasound sensor based on a slope-symmetric Fabry–Perot interferometer (FPI) is presented, employing dual-channel quadrature-biased heterodyne interrogation with an acousto-optic modulator (AOM). By introducing a 200 MHz frequency shift that yields an effective π/2 phase offset between the direct (unshifted) and frequency-shifted optical paths, the system ensures complementary sensitivity: when one channel operates at zero slope on the FPI transfer function (minimum sensitivity), the other resides at maximum slope, providing inherent immunity to laser wavelength drift and environmental perturbations. Experimental validation demonstrates reliable ultrasound detection across varying operating points. At quadrature extremes, one channel achieves peak amplitudes of ±2 V while the other is quiescent, whereas intermediate points enable simultaneous detection with amplitudes of ±1.5 V (AOM channel) and ±0.05–0.1 V (direct channel), accompanied by corresponding DC levels ranging from ~0.4 V to 1.6 V. The AOM channel utilizes simple envelope detection after 9.5–11.5 MHz bandpass filtering, maintaining low cost, though coherent mixing is suggested for enhanced weak-signal performance. The angle-symmetric FPI design, combined with gold-disk reflector adaptations and potential femtosecond laser micromachining, further reduces fabrication costs without sacrificing finesse or sensitivity. This quadrature-biased approach offers superior stability compared to single-channel systems, making it highly suitable for practical applications in photoacoustic imaging, nondestructive testing, and structural health monitoring. Full article

Beyond supporting ultra-high-capacity data transmission, metropolitan and access networks are expected to enable real-time infrastructure monitoring, driving the emergence of integrated sensing and communication (ISAC). Distributed acoustic sensing (DAS) has proven to be well-suited to urban sensing application requirements, yet its seamless integration into ISAC remains challenging—conventional high-peak-power sensing pulses in DAS induce nonlinear crosstalk in communication channels. DAS inherently suffers from interference fading due to single-frequency laser sources, which limits sensitivity. Here, we propose an ISAC architecture based on an electro-optic (EO) comb and a 7-core fiber, achieving nonlinearity-suppressed self-homodyne transmission and fading-suppressed DAS. Unmodulated comb lines and sensing pulses are polarization-multiplexed into orthogonal polarization states within the central core to minimize nonlinear crosstalk while delivering local oscillators (LOs) for wavelength division multiplexing (WDM) coherent transmission within six outer cores—achieving 10.56 Tbit/s capacity. In addition to supporting WDM transmission, the EO comb’s wavelength diversity is also exploited to enhance DAS performance. Specifically, a dual-pulse probe loaded onto four comb lines yields a 6 dB signal-to-noise ratio gain and a 64% reduction in fading occurrences, achieving a sensitivity of 1.72 $p\epsilon /\sqrt{\mathrm{Hz}}$ with 8 m spatial resolution. Moreover, our system supports simultaneous multi-wavelength backscatter detection in sensing and simplified digital signal processing in self-homodyne communication, reducing receiver complexity and cost. Our work presents a scalable, energy-efficient ISAC framework that unifies high-capacity communication with high-sensitivity sensing, providing a blueprint for future intelligent optical networks. Full article

In high-precision optical systems such as laser optics, astronomical observation, and semiconductor lithography, anti-reflection coatings are crucial for light transmittance, imaging quality, and stability, but traditional designs face modeling challenges in balancing ultralow reflectivity, high wavefront quality, and manufacturability amid multi-dimensional parameter coupling and multi-objective constraints. This study addresses these by proposing a unified mathematical modeling framework integrating a Symmetric five-layer high-low refractive index alternating structure (V-H-V-H-V) with dual-scale nanostructures, employing a constrained quasi-Newton optimization algorithm (L-BFGS-B) to minimize reflectivity, wavefront root-mean-square (RMS) error, and surface roughness root-mean-square (RMS) in a six-dimensional parameter space. The Sellmeier equation is adopted to calculate wavelength-dependent material refractive indices, the model uses the transfer matrix method for the Symmetric five-layer high-low refractive index alternating structure’s reflectivity, incorporates nano-surface height function gradient correction, sub-wavelength modulation, and radial optimization, applies Zernike polynomials for low-order aberration correction, quantifies surface roughness via curvature proxies, and optimizes via a weighted objective function prioritizing low reflectivity. Numerical results show the spatial average reflectivity at 632.8 nm reduced to 0.13%, the weighted average reflectivity across five representative wavelengths in the 550–720 nm range to 0.037%, the reflectivity uniformity to 10.7%, the post-correction wavefront RMS to 11.6 milliwavelengths, and the surface height standard deviation to 7.7 nm. This framework enhances design accuracy and efficiency, suits UV nanoimprinting and electron beam evaporation, and offers significant value for high-power lasers, lithography, and space-borne radars. Full article

This work presents, to the best of our knowledge, the first experimental report of an erbium/ytterbium double-clad ring fiber laser based on nonlinear polarization rotation (NPR) operating in a self-starting Q-switched high-order harmonic mode locking noise-like pulse (QHML-NLP) regime. The NPR mechanism relies on an arrangement composed of a beam splitter cube, a half-wave retarder, and a quarter-wave retarder. Through specific adjustments of the wave retarders and pump power, the laser cavity engages the QHML-NLP regime, where mode-locked burst-like pulses containing a significant number of NLPs are modulated by a giant Q-switched envelope. The laser system emits at the 132nd-order harmonic mode locking (HML) frequency, representing the highest order achieved to date in the framework of QHML-NLP. Additional features include a broadband optical spectrum with dual-wavelength emission at 1568.4 nm and 1605.9 nm, and maximum energies of 2.37 µJ for the Q-switched envelope and 200 nJ for the mode-locked burst-like pulse. These detailed experimental results reveal remarkable aspects in the NLP dynamics, contributing to a deeper understanding of their physical mechanisms and highlighting their potential as novel laser sources for micromachining and nonlinear optics. Full article

We experimentally and theoretically demonstrate coexistence of three different wavelength-multiplexed bound dual-frequency pulses in an all-fiber mode-locked fiber laser, effectively achieved by exploiting polarization-dependent loss effects and two uneven gain peaks of Er-doped fiber. With the single wall carbon-nanotube-based intensity modulation, wavelength-multiplexed dual-frequency pulses located at 1531.1 nm and 1556.6 nm are obtained. Changing the polarization rotation angles in the fiber cavity, one of the two asynchronous pulses evolves into a bound state of a doublet, in which the center wavelength of the bound solitons is centered at ~1530 nm or ~1556 nm. The relative phase between the two bound solitons or modulation depth of bound solitons can be switched by a polarization controller. A simulation method based on coupled Ginzburg–Landau equations is provided to characterize the laser physics and understand the mechanism behind the dynamics of tuning between different bound dual-frequency pulses. The proposed fiber laser will provide a potential way to understand multiple soliton dynamics and implementation in optical frequency combs generation. Full article

Background/Objectives: Alveolitis, or “dry socket,” is a common complication after tooth extraction, associated with pain, inflammation and delayed healing. Standard surgical treatments are often invasive and insufficient. Laser therapy offers antimicrobial, anti-inflammatory and regenerative effects. This study aimed to compare the efficacy of 980 nm monolaser therapy and 980 nm and 1550 nm dual-wavelength therapy on alveolar socket healing in a rabbit model. Methods: In vitro tests evaluated bactericidal effects of 980 nm laser exposure. Eighteen adult male chinchilla rabbits underwent the extraction of the first incisors with the prevention of clot formation to model alveolar socket healing. On day 3, animals were randomized to three groups: mechanical curettage and antiseptic irrigation, 980 nm diode laser therapy, or combined 980 nm + 1550 nm therapy. Clinical parameters (hyperemia, edema, pain, socket closure) were assessed up to day 7. Histological and microbiological analyses were performed on days 7 and 12. Results: Laser therapy showed superior outcomes compared to mechanical treatment. In vitro, 980 nm exposure eradicated microorganisms after 3 s. By day 7, hyperemia decreased to 0.7 ± 0.6 points in the dual-laser group, versus 2.0 ± 0.0 (980 nm) and 3.0 ± 0.0 (mechanical). Complete socket closure occurred in 33% with mechanical treatment and in 67% of sites in the dual-laser group. Pain was fully resolved only after dual-laser therapy. Histology confirmed more organized granulation tissue and angiogenesis in the dual-laser group. Conclusions: Dual-wavelength laser therapy demonstrated superior anti-inflammatory, antimicrobial and regenerative effects compared with diode monotherapy and mechanical treatment. These findings highlight its promise as a minimally invasive approach for managing alveolitis, warranting further clinical evaluation. Full article

A composite dual-cavity passively mode-locked fiber laser based on a functionalized microsphere resonator is proposed and experimentally demonstrated. The nonlinear response of the resonator is enhanced by depositing TiO₂ film on a SiO₂ microsphere, which leads to improved mode-locking performance. The wavelength selectivity and optical field confinement of the microsphere resonator are exploited, allowing it to simultaneously serve as an intracavity narrowband filter and a nonlinear modulation element. The threshold of the mode-locked laser was measured to be as low as 34 mW, and stable mode-locked operation was achieved at a pump power of 105.7 mW, with a pulse duration of 2.8 ns, a repetition rate of 13.88 MHz, and a signal-to-noise ratio of 74.86 dB. The output spectrum exhibited a central wavelength of 1560.12 nm, a 3 dB linewidth of 0.06 nm, and a side-mode suppression ratio of 55.13 dB. This straightforward design provides an effective approach for the miniaturization of passively mode-locked fiber lasers. Full article

Through this work, an experimental setup and pre-processing method for obtaining fluorescence and quasi-noise-free Raman spectra of minerals for in situ mineral identification in an underground environment is proposed. It uses a combination of methodologies like dual excitation wavelengths, Shifted Excitation Raman Difference Spectroscopy (SERDS), and deep learning-based U-Net model for background and noise correction. The dual excitation wavelengths technique employs a near-infrared SERDS laser for the fingerprint and a red laser for the large Raman shift region. The SERDS laser operates at two excitation wavelengths and is tuneable in the vicinity of 785 nm. The red laser uses 671 nm excitation wavelength. The obtained fingerprint and large Raman shift Raman spectra are then fed to a pre-processing method containing the trained U-Net model for obtaining a background-corrected and quasi-noise-free Raman spectrum. The proposed method addresses issues of existing handheld Raman systems in terms of spectrometer sensitivity, spectrum acquisition speed, pre-processing time, fluorescence effects, and other interferences due to surrounding light or vibration. The obtained final processed Raman spectrum is then deconstructed into pseudo-Voigt peaks. The identification of the minerals can be based on the number and the positions of the pseudo-Voigt peaks. Samples of gypsum (CaSO₄·2H₂O) and anhydrite (CaSO₄) were used for evaluating the performance of the proposed method. The influence of measurement time on the reproducibility and precision of the peak identification and, thus, mineral identification is also analyzed. Full article

Artificial supplemental lighting represents a crucial agricultural technique for enhancing plant growth and development, with researchers continuously investigating the effectiveness of various light sources in horticultural applications. Laser technology, characterized by its monochromatic nature, high coherence, and elevated energy density, presents a promising light source whose potential applications and underlying mechanisms in plant supplemental lighting remain to be thoroughly explored. To investigate the effects of different red-to-blue light ratios in laser supplemental lighting on rice (Oryza sativa L. cv. Jijing129) seedlings, we conducted a seedling-stage lighting experiment on the rice cultivar Jijing129 in a greenhouse using an LGI-660/450 dual-wavelength semiconductor laser system. The experimental design included a natural light control (AL) and three laser treatment groups, with red: blue (R:B) ratios and corresponding photon flux densities as follows: BL (50:50; 150:150 μmol m⁻² s⁻¹), CL (60:40; 180:120 μmol m⁻² s⁻¹), and DL (75:25; 225:75 μmol m⁻² s⁻¹). We systematically analyzed short-term morphological, physiological, and gene expression changes to elucidate the potential mechanisms underlying yield enhancement under different laser spectra. The results indicated that, compared to AL, all laser treatments (BL, CL, and DL) significantly increased root fresh weight, dry weight, and nitrogen content in seedlings. Furthermore, the final yield was significantly improved in all laser-treated groups, with the CL treatment exhibiting the highest yield. Transcriptome sequencing identified 10,497, 10,441, 10,700, and 10,757 expressed genes in the AL, BL, CL, and DL groups, respectively. Comparative analysis revealed 101, 1645, and 2247 differentially expressed genes (DEGs) in the BL/AL, CL/AL, and DL/AL comparisons, respectively. Gene Ontology (GO) enrichment analysis showed that these DEGs were significantly enriched in pathways such as metabolic processes, nitrogen metabolism, and protein amino acid phosphorylation. Notably, genes involved in the regulation of nitrogen compound metabolism were significantly upregulated in the CL and DL treatments. Further analysis of nitrogen metabolism and photosynthesis pathways revealed that laser irradiation induced the upregulation of specific genes. Interestingly, although physiological assays showed no significant changes in CAT, SOD, and POD activities, the expression of their corresponding genes was upregulated by laser treatment, suggesting these genes play a regulatory role during the supplemental lighting process. Therefore, our results indicated that laser supplemental lighting during the rice seedling stage increased the nitrogen content in plants and modulated the expression of related genes, and these changes might have been associated with the subsequent increase in rice yield. This study lays a foundation for understanding the molecular mechanisms of laser supplemental lighting and provides empirical support for the application of laser technology as an effective light source in agriculture. Full article