Search Results (68)

A continuous-wave (CW) orthogonally polarized single-wavelength red laser (OPSRL) at 698 nm with a tunable power ratio within a wide range between the two polarized components was demonstrated using two Pr³⁺:LiLuF₄ (Pr:LLF) crystals for the first time. Through control of the waist location of the pump beam in the active media, the output power ratio of the two polarized components of the OPSRL could be adjusted. Under pumping by a 20 W, 444 nm InGaN laser diode (LD), a maximum total output power of 4.12 W was achieved with equal powers for both polarized components, corresponding to an optical conversion efficiency of 23.8% relative to the absorbed pump power. Moreover, by a type-II critical phase-matched (CPM) BBO crystal, a CW ultraviolet (UV) second-harmonic generation (SHG) at 349 nm was also obtained with a maximum output power of 723 mW. OPSRLs can penetrate deep tissues and demonstrate polarization-controlled interactions, and are used in bio-sensing and industrial cutting with minimal thermal distortion, etc. The dual-polarized capability of OPSRLs also supports multi-channel imaging and high-speed interferometry. Full article

Under the framework of classical electrodynamics, this article investigates the nonlinear Thomson scattering generated by the cross-collision between a tightly focused linearly polarized Gaussian laser pulse and a relativistic electron through numerical simulation and emulation. The oscillation direction and emission angle of the electron’s trajectory are influenced by the beam waist radius and the delay time. The spatial radiation distribution of electrons exhibits a comet-shaped pattern, with the radiation being concentrated in the forward position. This is attributed to the high laser intensity at the focus, resulting in intense electron motion. As the beam waist radius keeps increasing continuously, the maximum radiation polar angle in the spatial distribution decreases. The time spectrum exhibits a symmetrical three-peak structure, with a high secondary peak. Meanwhile, the supercontinuum spectrum gradually transforms into a multi-peak distribution spectrum. In the multi-peak mode, the main peak and the secondary peak will interchange during the increase in the waist radius, generating rays with higher frequencies and energies. The aforementioned research findings reveal a portion of the mechanism of the nonlinear Thomson scattering theory and are beneficial for generating X-rays of higher quality. Full article

Wavelength modulation spectroscopy off-axis integrated cavity output spectroscopy (WMS-OA-ICOS) is an in situ detection technique suitable for analyzing trace gases in the atmospheres, characterized by its high sensitivity and ease of integration. However, in current practical applications, the design and optimization of WMS-OA-ICOS systems primarily rely on empirical knowledge, lacking systematic quantitative methodologies. To address this limitation, this study conducts comprehensive modeling and simulation research on WMS-OA-ICOS spectroscopy, proposing a novel modeling approach. The spot distribution simulation results obtained from the self-developed model are validated against those generated using Tracepro. Furthermore, based on the self-developed model, an in-depth investigation is conducted into the effects of cavity length tolerance, beam waist matching, modulation depth, and laser linewidth on signal quality. The findings provide valuable insights for designing and optimizing miniaturized systems with high signal-to-noise ratios. Full article

The interaction of a Gaussian vortex beam (GVB) with metamaterials during its propagation is of significant interest to the optical community. These GVBs are classified as structured light beams that possess orbital angular momentum (OAM). Understanding the behavior of structured light beams is essential for clarifying fundamental interaction mechanisms with metamaterial structures. So, this work delves into the investigation of the propagation characteristics of a GVB within a chiral material. The analytical expressions for GVB propagating through a chiral medium are obtained by using the extended Huygens–Fresnel diffraction integral formula and the optical ABCD matrix system. In a chiral medium, GVB exhibits a tendency to fragment into a left circularly polarized (LCP) beam and a right circularly polarized (RCP) beam, each following its unique propagation paths. The beam intensity and gradient force are computed and discussed for OAM mode number, beam waist radius, and chirality parameter. This research will be quite helpful for light manipulation, optical sorting, optical radiation force, the radiative transfer process, and optical guiding. Full article

Improving the efficiency of lasers without complex structures, expensive elements, and precise optimization will lead to cost reductions and increased practicality. Here, it is first shown theoretically that the dependence of the optical-to-optical conversion efficiency on the laser beam waist (minimum laser spot) radii for a Yb:YAG laser with a simple structure decreases extremely with increasing pump intensity and efficiency. Not only is the optimum range for highest efficiency wide, but even if the radii are doubled, the efficiency decreases by only a few percentage points or less at the maximum pump intensity of 450 kW/cm². Therefore, it is possible to achieve sufficiently high efficiencies without precise optimization by high-intensity pumping. In the experiment, at a pump wavelength of 940 nm, corresponding to pump-level pumping, the maximum efficiency was 75.2% for the incident pump power at the corresponding maximum intensity. On the other hand, at a pump wavelength of 968 nm, corresponding to direct pumping of the upper laser level, the maximum efficiency was 76.0% at about 60% of the maximum. Although the pump focus is slightly off from the optimum, these efficiencies are close to the theoretical maximum at the corresponding pump intensities. Since no complex gain medium is used, there is almost no efficiency reduction due to parasitic oscillations, despite the high pump intensities. These results demonstrate the high practicality of high-intensity pumping for high-efficiency lasers. Full article

Current distance limitations of quantum key distribution (QKD) over fibre optic networks suggest that satellite (free-space optical) QKD networks will be required to enable global quantum communications. However, the operational availability of these systems is limited by background noise and strong attenuation caused by turbulence and adverse weather conditions. Using the decoy-state BB84 QKD protocol, we evaluate the secret key rate for a range of wavelengths, receiver sizes and initial beam waists through a variety of atmospheric conditions. We combine filtering techniques, adaptive optics, and wavelength selection to optimize the performance of satellite QKD. This study is simulation-based. Full article

Terahertz (THz) molecular fingerprint spectroscopy provides a powerful label-free tool for detecting trace-amount analytes. Introducing extra microstructures such as metasurfaces to confine the field energy is essential to improve the sensitivity. However, the area of analyte film on conventional enhancing metasurfaces must be larger than the beam spot in a free-space measuring setup. Here, we propose a tunable defect cavity of one-dimensional photonic crystal in the combined coaxial waveguide (CCW) and enhance the broadband THz fingerprint of trace analytes on a much smaller area. The peaks of high Q resonances can form a wide absorption spectrum by changing the length of the rubber part of the coaxial waveguide. For the 0.2 µm α-lactose film sample in the frequency range of 0.48–0.58 THz, the absorption enhancement factor of 89.2 times based on the thickness can be achieved and the sample area is about 1/1700 of that in the free-space measurement with the 5 mm beam waist. We first introduce the coaxial waveguide in the terahertz absorption spectra enhancement. With our proposed structure the analyte volume is effectively reduced which is significant in the real application scenario. Full article

Direct laser acceleration with radially polarized lasers is an intriguing variant of laser-based particle acceleration that has the potential of offering GeV/cm-level energy while avoiding the instabilities and complex beam dynamics associated with plasma wakefield accelerators. A major limiting factor is the difficulty of generating high-power radially polarized beams. In this paper, we propose the use of CO₂-based long-wave infrared (LWIR) lasers as a driver for direct laser acceleration, as the polarization insensitivity of the gain medium allows a radially polarized beam to be amplified. Additionally, the larger waist sizes, Rayleigh lengths, and pulse lengths associated with the long wavelength could improve the injection efficiency of the electron beam. By comparing acceleration simulations using a near-infrared laser and an LWIR laser, we show that the injection efficiency is indeed improved by up to an order of magnitude with the longer wavelength. Furthermore, we show that even sub-TW peak powers with an LWIR laser can provide MeV-level energy gains. Thus, radially polarized LWIR lasers show significant promise as a driver of a direct laser-driven demonstration accelerator. Full article

Blue lasers are integral to a variety of applications, including marine communication, underwater resource exploration, cold laser processing, laser medicine, and beyond. Vertical external cavity surface-emitting lasers (VECSELs) have the advantages of high output power and tunable wavelength, and can output blue laser via frequency doubling. In this article, a new type of intracavity beam control external-cavity structure is introduced. The laser beam waist is effectively adjusted by intracavity beam control, and the frequency conversion efficiency is improved. A laser cavity stability analysis model was developed to investigate the impact of laser cavity lens parameters and relative positions on stability. The external resonant cavity of VECSELs utilizes two optical lenses to position the beam waist near the laser output coupling mirror and locates the frequency doubling crystal at a high optical power density position to optimize frequency conversion efficiency. The VECSEL straight external-cavity structure achieves a frequency conversion efficiency of up to 60.2% at 488 nm, yielding a blue laser output exceeding 1.3 W. The full width at half maximum of the 488 nm spectrum measures approximately 0.23 nm. This intracavity beam-controlled direct external-cavity structure effectively mitigates laser mode leakage and shows potential for the development of an efficient and compact blue laser source. Full article

In the context of reinforced concrete (RC) arch bridges, while the incorporation of full sections of steel fibers can enhance the bridge’s toughness, cracking resilience, and bearing capacity, achieving an optimal balance between structural performance and economic viability in this manner remains challenging. This article introduces a novel computational approach—the distributed steel fiber concrete (LSFRC) arch—which considers the spatial distribution of damage in RC arches. The static performance of SFRC elements and LSFRC beams was compared and analyzed using the concrete plastic damage model (CDP) in ABAQUS software. This study validated the rationality of the model and investigated the impact of varying steel fiber volume ratios and steel fiber layer heights on the damage evolution of LSFRC arches. The results of this study demonstrate that the cracking load and bearing capacity of an RC arch can be effectively enhanced through the addition of steel fibers to a local area under static loading. Furthermore, the deflection and damage to the arch waist and arch roof can be significantly reduced. Furthermore, the incorporation of steel fibers at an increased volume rate and at a greater height within the doped section can effectively slow the rate of damage evolution within the section. This results in the inhibition of crack extensions and in an improvement in the ductility and reliability of the damage stage. The LSFRC arches offer superior economic and practical advantages over their full cross-section doped steel fiber (FRC) counterparts. This study offers novel insights and methodological guidance for the design and implementation of concrete arch bridges. Full article

We derive the analytical expressions for root-mean-square (rms) beam wander (BW) and relative BW of a twisted electromagnetic elliptical vortex (TEEV) beam propagating through non-Kolmogorov atmospheric turbulence with the help of the extended Huygens–Fresnel principle and the second-order moments of the Wigner distribution function (WDF). Our numerical findings demonstrate that the BW of a TEEV beam with a small ellipticity, a large topological charge as well as a small waist width and initial coherent length is less affected by the turbulence. It can be also found that the effect of turbulence with a larger outer scale of turbulence, a generalized exponent parameter, and a generalized structure parameter on BW is more obvious. It is interesting to find that the effect of atmospheric turbulence on BW for a TEEV beam can be effectively reduced by regulating jointly the symbols and sizes of the twisted factor and topological charge. Therefore, modulation of the structure parameters of a TEEV beam provides a new way to mitigate turbulence-induced beam wander. Our work will be useful for free-space optical communications, remote sensing, and lidar distance measurement. Full article

We designed a narrow-linewidth external-cavity hybrid laser leveraging a silicon-on-insulator triple Euler gradient resonant ring. The laser’s outer cavity incorporates a compact, high-Q resonant ring with low loss. The straight waveguide part of the resonant ring adopts a width of 1.6 μm to ensure low loss transmission. The curved section is designed as an Euler gradient curved waveguide, which is beneficial for low loss and stable single-mode transmission. The design features an effective bending radius of only 26.35 μm, which significantly improves the compactness of the resonant ring and, in turn, reduces the overall footprint of the outer cavity chip. To bolster the laser power and cater to the varying shapes of semiconductor optical amplifier (SOA) spots, we designed a multi-tip edge coupler. Theoretical analysis indicates that this edge coupler can achieve an optical coupling efficiency of 85%. It also reveals that the edge coupler provides 3 dB vertical and horizontal alignment tolerances of 0.76 μm and 2.4 μm, respectively, for a spot with a beam waist radius of 1.98 μm × 0.99 μm. The outer cavity, designed with an Euler gradient micro-ring, can achieve a side-mode suppression ratio (SMSR) of 30 dB within a tuning range of 100 nm, with a round-trip loss of the entire cavity at 1.12 dB, and an expected theoretical laser linewidth of 300 Hz. Full article

To investigate the mechanical behavior and design methodology of column-free QRST (quasi-rectangular segmental tunnel) structures, a theoretical analysis based on prototype experiments and simulation models is conducted. Initially, a prototype experimental investigation is conducted to reveal the structural behavior at the service stage. Subsequently, the ESHR model (Equivalent Stiffness Homogeneous Ring), the BS model (Beam Spring), and the MBS model (Modified Beam Spring) are used to simulate structural behavior. For design purposes, the design methodology is explored based on the ESHR model, followed by a sensitivity analysis of several key load parameters. Based on the experimental results, weak parts of the column-free QRST structure are found to include several joints (Joint 1, Joint 5, Joint 3, and Joint 8), and corresponding optimization measures are proposed. By comparing the test results, the above-mentioned three models demonstrate their applicability in structural simulation, with the ESHR model having sufficient design accuracy. A model-based deformation mechanism analysis found that joints contribute approximately 2/3 of the structural deformation. For the structural design of the column-free QRST using the ESHR model, amplifying the calculated results of structures directly subjected to the service stage by 10% suffices to meet engineering requirements. Based on the test and study, special attention should be paid to the negative bending moment regions at the waists of the structure during both the design and service stages. Full article

Near-field bending of a laser diode bar (i.e., the SMILE effect) degrades the laser beam brightness, adversely affecting optical coupling and beam shaping. Previous reports mainly focused on the two-dimensional near-field bending of a laser diode bar. However, the near-field bending of a laser diode bar not only occurs in the laser bar growth direction, but also in the beam propagation direction. The present article proposes the three-dimensional near-field bending of a laser diode array, which is commonly known as the three-dimensional spatial SMILE effect. Through theoretical and simulated investigations, it has been found that a laser bar array not only deforms in the fast axis direction to cause the traditional two-dimensional SMILE effect but also experiences an additional deformation of approximately 2 μm in the laser emission direction simultaneously. Due to the SMILE effect in the beam propagation direction, not all emitters are aligned in a straight line, and some emitters experience defocusing during collimation. Consequently, there is an increase in the residual divergence angle and beam width, resulting in a degradation of the laser bar array’s beam quality. According to the theoretical calculations, ZEMAX simulations, and experimental results, for a FAC (fast axis collimation) with a focal length of 300 μm, the divergence angle of single emitter after collimating in the fast axis increases from 4.95 mrad to 6.46 mrad when the offsetting of the working distance between the incident beam waist and FAC lens increases from 0 μm to 2 μm. Full article

The increasing enhancement in the modulation accuracy of spatial light modulators has garnered significant attention towards real-time control technology for light fields based on these modulators. It has been demonstrated that this technology possesses a remarkable capability to generate vector beams with arbitrary complex amplitude distributions. Nevertheless, past studies indicate that the generation of only one vector beam at a time has been observed. The simultaneous generation of numerous vector light fields can give rise to several challenges, including compromised picture quality, limited single-mode operation, and intricate optical path configurations. In pursuit of this objective, we present a novel methodology that integrates the coding methodology of modified off-axis interferometric holography with the idea of optical superposition. This technique facilitates the concurrent generation of several vector beams. In this study, we present a demonstration of the simultaneous creation of twelve vector beams using a single spatial light modulator (SLM) as a proof of concept. Significantly, this technology has the ability to generate an unlimited quantity of vector light fields concurrently under the assumption that the resolution of the SLM does not impose any limitations. The findings indicate that the imaging quality achieved by this technology is of a high standard. Furthermore, it is possible to separately control the beam waist radius, topological charge, polarization order, and extra phase of each beam. Full article