We report a fabrication method for the (8 + 1)×1 pump and signal combiner (PSC) and investigate its pump light transmission characteristics. It employs three specifications of fibers: the pump fiber is 220/242 µm and NA = 0.22; the signal fiber is 25/250 µm and NA = 0.065/0.46; the double-clad fiber (DCF) is 20/400 µm, and NA = 0.065/0.46. Based on the arrangement characteristics of the pump fibers and signal fiber, as well as the principle of brightness conservation, the optimal preparation parameters for the (8 + 1)×1 PSC are determined. In order to optimize the performance of the PSCs with different numbers of pump ports, the transmission efficiencies of pump light and pump light divergence angles are calculated for pump port numbers of 6, 7, 8, 9, 10, and 11, respectively. The results indicate that the maximum number of pump ports it can support is 8. Experimental results show that the transmission efficiencies of pump light and signal light are 98.20% and 96.66%, respectively. The measured beam quality of the (8 + 1)×1 PSC is M2 = 1.19, and the beam quality degradation is ΔM2 = 0.10. The total pump power is 5.736 kW, which is limited by the pump powers of the laser diodes (LDs). Compared to the (6 + 1)×1 PSC fabricated using the same method, the pump power increased by 1.604 kW. When the pump powers of both are approximately 4 kW, the temperature of the DCF coating layer in (8 + 1)×1 PSC is 17.8 ℃ higher than that in the (6 + 1)×1 PSC. The divergence angle of pump light combined by the (8 + 1)×1 PSC is 1.007 rad, and the experimental results are in good agreement with the simulation results.

Piecewise parabolic phase modulation, in which the optical spectrum linewidth is equal to the product of its chirp rate and period, is believed to be promising in SBS suppression, as it can yield a nearly flat-top optical spectrum. However, no kilowatt-level laser output has been achieved with this scheme because of its high sampling rate dependency on arbitrary waveform generators. In this paper, its high dependency on high sampling rate is theoretically discussed based on fast Fourier transform. We propose and experimentally validate two approaches to mitigate the dependence on sampling rate: extrema clamping, in which the local maxima and minima of the waveform are reassigned, and increasing the modulation depth as a means of further relaxing the sampling rate requirement. We established an amplifier system which includes a piecewise parabola phase-modulated single-frequency fiber laser, a two-stage pre-amplifier, and a counter-pumping main stage, subsequently. Finally, a 7.56-GHz piecewise parabola phase-modulated, 1750-W MOPA fiber amplifier, is experimentally achieved.

Power scaling of high-power narrow-linewidth continuous-wave fiber lasers is limited by stimulated Brillouin scattering (SBS). While inversion probability-tunable (p-tunable) sequence modulation offers dynamic spectral control for enhanced SBS suppression, its practical implementation has been hindered by reliance on complex, expensive arbitrary waveform generators (AWG) or significant hardware complexity (particularly demanding logic resource requirements) of conventional field-programmable gate array (FPGA)-based implementations. This work introduces what we believe to be a novel, hardware-efficient approach to overcome these limitations. We present a hardware-efficient parallel linear feedback shift register (LFSR) architecture with comparator probability adjustment, enabling real-time, precise p-value control at 10 GHz clock rates, significantly reducing cost and complexity. Concurrently, we establish a quantitative acoustic-photonic dynamics model based on a time-dependent three-wave coupled equation, solving the nonlinear interactions among signal laser photons, phonons, and Stokes waves under p-tunable modulation. This model enables systematic optimization, theoretically predicting and experimentally confirming maximal SBS threshold enhancement at p = 0.58. Leveraging this optimized parameter, our system achieves 2.82 kW output power with a 10.34 GHz FWHM linewidth. Compared to systems using pseudo-random binary sequence (PRBS) modulation (achieving 2.46 kW at ∼10 GHz FWHM linewidth), this represents a 13% increase in output power. This integrated hardware-theory solution provides a practical and effective approach for SBS suppression in high-power narrow-linewidth fiber lasers, enabling higher power scaling and stable operation.

High-power narrow-linewidth fiber lasers combine compact structure, efficient thermal management, and high electro-optical conversion efficiency, making them highly attractive for applications such as coherent beam combining and nonlinear frequency conversion. However, further power scaling is severely constrained by nonlinear effects, particularly stimulated Brillouin scattering (SBS), during power amplification. In this work, we propose a high-order phase modulation scheme based on binary sequences with a controllable inversion probability to achieve tunable spectral broadening of the seed laser, thereby effectively suppressing the SBS effect and enhancing the amplifier output power. An inversion-probability-tunable sequence generation method based on a linear feedback shift register (LFSR) is developed and experimentally implemented. Using a three-stage fiber amplifier, a maximum output power of 3.0 kW is achieved with an 11.4 GHz FWHM linewidth. Under the same spectral broadening bandwidth, the output power is increased by 16% compared with pseudo-random binary sequence (PRBS) modulation and by 25% compared with conventional random-number-based p-tunable sequence modulation.

We present a primary off-axis reflective laser beam expander based on a spherical secondary mirror and a high-order aspheric primary mirror configuration. The system processes an input laser power exceeding 10 kW, with a beam diameter of 15 mm @1/e2, and delivers an expanded beam diameter of 60.4 mm @1/e2, with maintaining a compact weight of 2.9 kg. To address thermal effects during beam expansion, we employed an integrated opto-thermo-mechanical analysis approach, utilizing finite element methods to investigate the temporal evolution of optical characteristics under both normal incidence and near-field beam offset conditions. The primary mirror uses glass-ceramics, whereas two secondary mirror materials were evaluated: sapphire and glass-ceramics. Experimental validation was conducted on the sapphire secondary and glass-ceramics primary configuration at 10.11 kW laser power for 140 s operation. Maximum temperature rises reached 9 degrees C (primary) and 14 degrees C (secondary). With 4 mm near-field beam offset, the expanded beam maintained beta(max )= 1.26, beta(avg )= 1.14, and the laser source exhibits an optical axis jitter of <8 mu rad, and the beam-expanded optical axis variation remains below 25 mu rad. This demonstrates that the beam expander is rationally designed with excellent high-power laser beam expansion performance and incident optical axis adaptability, providing references for the design and simulation of high-power (10-kW class) laser beam expansion, as well as for laser transmission beam quality and pointing control.

Phase modulation optical spectral broadening has been widely used as an effective stimulated Brillouin scattering suppressing scheme in narrow linewidth fiber amplifiers. In particular, tunable inversion probability sequence (p-tunable sequence) phase modulation effectively optimizes the spectral envelope, improving the SBS threshold in a monolithic narrow linewidth fiber amplifier. This paper theoretically and experimentally investigates the SBS suppression capability of p-tunable phase modulation. Firstly, we introduce a theoretical model to illustrate, for the first time, the temporal and spectral properties of light waves that have been phase-modulated by a p-tunable sequence. An optimization scheme for parameter selection of p-tunable sequence phase modulation is established by calculating the SBS threshold. Meanwhile, we establish a three-stage fiber amplifier system with p-tunable phase modulation to verify our theory. The output power is 2390 W with an FWHM optical linewidth of 10 GHz. Compared to the pseudo-random binary sequence (PRBS) case, this scheme increases the output power by 700 W at 10 GHz FWHM optical linewidth.

We demonstrate the capability to suppress stimulated Brillouin scattering (SBS) in a high-power all-fiber laser amplifier system using filtered and amplified pseudo-random binary sequence (PRBS) phase modulation techniques. Based on the time-dependent three-wave coupled SBS interaction equations in an amplifier model consisting of active fiber and passive fiber and spectral calculation of phase modulation, we numerically simulate the dependence of the normalized SBS threshold and the root-mean-square (RMS) linewidth on both the filter cutoff frequency and the phase modulation depth for filtered and amplified PRBS phase modulation at a fixed clock rate with different pattern lengths. PRBS9 is superior to other investigated patterns. A set of optimal pattern lengths, RMS modulation depths, and the ratio of the filter cutoff frequency to the clock rate are determined. Specific time-domain details of the variation of the RF signal with experimentally measured RMS modulation depth are shown. The dependence of different time-domain waveforms and their corresponding spectra and SBS thresholds on the RMS modulation depth is illustrated by theoretical predictions and experimental measurements, and the optimal value of the RMS modulation depth is demonstrated. Then, both the RMS linewidth of the optical spectra and the maximum normalized SBS threshold under the optimized parameters increase linearly with clock rate. While, with the further increase of the clock rate to ∼14 GHz, the SBS threshold reaches a saturation point when the maximum effective spectral linewidth is reached, where the spectral line spacing is half of the FWHM Brillouin linewidth, and the optimal spectral line spacing is not affected by the fiber length of the system. Eventually, a laser power output of 2.78 kW at an FWHM linewidth of 9.95 GHz is experimentally obtained.

Objective High-power fiber lasers and their sub-beam combining technology are effective for achieving high-brightness and high-power laser outputs. With the continuous improvement of output laser power and energy concentration in the research and development of high-power laser system engineering, multiple sub-beam lasers are required to operate simultaneously for system testing. The output sub-beam laser exhibits high power density, a small divergence angle, and strong destructiveness. To prevent damage to the test environment and ensure personnel safety, a laser absorption device is necessary to effectively absorb and control multi-channel high-power-density laser energy. This ensures a high-efficiency, pollution-free, and safe testing process. When a multi-channel high-power-density laser is incident on the absorber, light-field coupling can cause excessive local temperature rise inside the absorber, leading to laser melting, structural deformation, and debris attachment. These issues pollute the optical environment and damage both the absorber and the laser output end. Additionally, excessive reinjection of laser return power into the laser causes the laser to burn out. To address the effective control requirements of multi-channel high-energy lasers in high-power laser system development, a laser absorption device is designed for the test system, and its thermo-optical characteristics are analyzed through simulations and experimental studies. Methods A novel three-channel high-power-density laser beam absorption device is designed. Unlike single-aperture absorption devices, multi-beam lasers exhibit a small divergence angle, a small spot size, high power density, and independent distribution. A discrete light-cone arrangement is employed for single-channel reflection beam expansion and multiple coupling absorption. Combined with an inner surface absorption coating and a surrounding extinction microstructure, the multi-aperture structure can independently absorb sub-beam laser energy simultaneously. Additionally, the fully sealed design of the absorption cavity allows for internal gas replacement through charging and exhaust mechanisms, ensuring the cleanliness and purity of the internal medium atmosphere while maintaining the safety of the light output. Based on beam tracing analysis, combined with the parameters of the beam-expanding cone, the absorber substrate material, the coating absorption coefficient, and the surface microstructure, the light field distribution on the internal absorption surface after coupling and superposition of the three-beam laser fields is simulated. The distribution pattern of the peak intensity and position of the internal light field, as well as the influence of the cone-tip fillet on internal light field distribution, is analyzed. The temperature rise in various regions inside and outside the absorber is quantitatively calculated using laser irradiation at 10.4 kW for 135 s. A three-beam high-power light output test is conducted to verify absorption temperature rise, anti-damage performance, and return power. Results and Discussions The new laser absorber is studied using simulation analysis and experimental testing. The simulation results show that the sub-beam laser power is 3.5 kW, and the three-beams emit light simultaneously at a total power of 10.5 kW. After passing through the expanding light cone, the optical power density on each absorption surface inside the absorber is effectively attenuated. Following beam coupling, the light field is superimposed onto the absorption area. The absorbed power in the light cone area is 5418.2 W, while the sidewall absorbs 3495 W (Fig. 4). The fiber end cap installation surface absorbs 5.05 W, and the optical aperture of the fiber end cap absorbs 0.06 W (Fig. 7). The radius of the cone tip significantly influences the laser power distribution on the bottom and side surfaces but has little effect on the return power (Fig. 8). At an ambient temperature of 20 degrees C, when the three-beam laser operates at 10.4 W@135 s, the highest internal temperature of 131.667 degrees C is observed near the light cone (Fig. 5). The highest external temperature of 74.4 degrees C is recorded outside the heat insulation board in the top absorption area (Fig. 6). A high-power light output test is conducted. For a single laser output of 3.5 kW@135 s, the maximum temperature rise at the end cap is 5 degrees C, and the maximum temperature rise at the front end is 15.8 degrees C (Fig. 12). When the three-beam laser operates at 10.4 W@135 s, the maximum external surface temperature of the absorber reaches 79.1 degrees C, with a temperature rise of 59.1 degrees C, occurring on the sidewall of the absorber ring. The highest temperature location relatively aligns with the simulation results (Fig. 13). The detected return light power is 130 mW, and the return light throughout the entire system remains within the safety threshold (Fig. 11). Conclusions To address the challenges of multi-beam output lasers with small beam diameters, high power densities, and small divergence angles, a new three-channel high-power-density laser absorption device is designed. The device incorporates optical cone beam expansion, cavity multiple coupling absorption, and stray light suppression. Using the beam-tracing method, simulations and experimental studies are conducted to analyze the laser field distribution inside the absorber, the influence of return power, the effect of cone tip radius, and the temperature rise distribution during the light output process. The temperature distribution of the absorber aligns with the simulation results. The full-link laser return power remains below the safety threshold, and the absorption temperature rise, anti-damage capability, and laser return power suppression effects are successfully verified. This research provides valuable insights for the efficient absorption of multi-channel high-power-density lasers, the design of measurement devices, and the studies on internal anti-damage mechanisms and return-light suppression. The findings can be extended to the development of similar applications in high-power laser systems.

We report a fabrication method for addressing the non-uniform arrangement issues associated with the asymmetric tapered fiber bundles (TFBs) in high-power pump and signal combiners (PSCs), which do not require pre-treatment of the pump fibers. It employs a homemade thin-walled glass tube with the coating layer, and six pump fibers surround it evenly to collectively form the TFB, while the signal fiber remains unaffected during the tapering process of the fiber bundle. The 3D simulation model of the backward (6+ 1)x1 PSC was established by the refractive index distribution method to calculate the transmission efficiency of the pump light and signal light, and then identify the optimal preparation parameters for achieving the best efficiency. In this model, a simulated quasi-uniform energy distribution light field was used as the input of the pump fiber, which can optimize the previous calculation method. Experimental results exhibited that the backward (6+ 1)x1 PSC achieved signal light and pump light transmission efficiencies of over 96% and 98%, respectively, the beam quality degradation is triangle M2 = 0.09, and the total output pump power was 4.102 kW. The experimental results are in good agreement with the simulation results. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

The output power of a single-beam fiber laser has a theoretical limit,and high-power fiber laser beam combining technology is the key to achieving ultra-high power while maintaining high beam quality.This paper analyzes on the limiting factors for power increasing in high-power fiber lasers,and reviews principles,technical characteristics,and current technological statuses of different beam combining schemes.Among these,chromatic beam combining using dichroic mirrors demonstrates significant engineering advantages for power increasing and beam quality preservation in broadband laser systems.The paper reviews the developmental progresses in pulsed and continuous wave fiber laser chromatic beam combining technologies in both domestically and internationally,introduces key technologies and researches in this field.Finally,future prospects for chromatic beam combining technology are discussed.

We report a theoretical and experimental study on stimulated Brillouin scattering (SBS) suppression in a monolithic fiber amplifier with filtered and amplified pseudo-random binary sequence (PRBS) phase modulation. Theoretically, we use a time-dependent three-wave coupled nonlinear system considering both active fiber and passive fiber to describe the acoustic phonon, laser, and Stokes characteristics in a fiber amplifier. The SBS threshold power after filtered PRBS phase modulation is numerically evaluated to obtain the optimal parameters, and the time-averaged distributions of the counter-pump power, laser power, and Stokes power at different positions along the fiber length of the fiber system are simulated. Also, we established a four-stage fiber amplifier system to verify our theory. The configuration of the fiber amplifier system includes a filtered and amplified PRBS phase-modulated single-frequency fiber laser, a three-stage pre-amplifier, and a counter-pumping main stage, subsequently. 2.5 kW output power with an FWHM linewidth of 9.63 GHz is accomplished by a domestic ytterbium-doped double-clad fiber with core/cladding diameters of 20.2/400 µm. The reflectivity of the main stage is 0.049‰ at the maximum output power, which indicates the proposed architecture is under the SBS threshold. The experiments verify the accuracy of the theoretical model, which provides a reliable reference for evaluating the SBS suppression capability of the high-power narrow-linewidth fiber amplifier phase modulated by the filtered and amplified PRBS signal.

In this study, a fusion splicing system that facilitates the splicing of a monolithic linear array fiber end cap is constructed. The fusion splicing thermal field of the end cap irradiated by a CO2 laser is theoretically simulated using the finite element method. The experimental fusion splicing temperature agrees well with the simulation results. The splicing strength, misalignment, and high-power withstanding capacity of the fusion-spliced monolithic linear 3-fiber end cap are investigated. The use of the fabricated device in a dual-grating spectral beam combination (SBC) is also demonstrated with three-channel laser beams, achieving a combined beam with near-diffractionlimited beam quality M-2 = 1.101. It shows that the development of the monolithic linear array fiber end cap is meaningful for achieving a compact high-brightness SBC system.

In this paper, we establish a multi-stage fiber amplifier with pseudo-random binary sequence (PRBS) phase modulation. The stimulated Brillouin gain spectra of the main amplifier with both the unmodulated and pseudo-random binary sequence phase modulated configuration are measured (with corresponding output power), and the stimulated Brillouin scattering (SBS) threshold is investigated experimentally and theoretically. The pseudo-random binary sequence phase modulation parameters are optimized by theoretical simulation. With a two-stage preamplifier chain and a counter-pumping main amplifier stage, a maximum 3.05 kW output power with a slope efficiency of 85.9% is obtained experimentally. The central wavelength of the fiber amplifier is 1050 nm, associated with a full-width at half-maximum linewidth of 13.7 GHz. The stimulated Brillouin scattering reflectivity is below 0.01% at 3.05 kW at 13.7 GHz, which indicates that stimulated Brillouin scattering can be suppressed efficiently at this power and linewidth level.

Stimulated Raman scattering (SRS) must be suppressed owing to its adverse effect on high-power fiber lasers. We propose a bending-sensitive multi-ring fiber composed of three parts: a core, multiple high-refractive-index rings, and a cladding. Appropriate bending of the fiber produces a high loss of the first-order Raman Stokes wavelength at 1114 nm and low loss of the signal wavelength at 1064 nm, thus enabling the signal light to be confined to the core while maintaining single-mode transmission. This principle relies on the resonant coupling between the core and ring modes. Numerical analysis indicated that the loss ratio of the fundamental mode could reach 2650.041 by optimizing the structural parameters. Moreover, when the three-ring fiber was subjected to a bending radius of 6 cm, a bend-induced loss of the Raman wavelength reached 11.315 dB/m, which effectively suppressed the first Stokes SRS generation. (c) 2024 Society of Photo-Optical Instrumentation Engineers (SPIE)

高功率窄线宽光纤激光器在遥感测量、引力波探测、光束合成等领域中应用广泛，但硅基光纤中的受激布里渊散射效应限制了其输出功率。对单频种子源进行相位调制以展宽线宽是常见的抑制受激布里渊散射的方法。然而，单一机理的射频相位调制对受激布里渊散射效应的阈值提升能力有限，已经不能满足近5 kW的激光功率需求。分析了伪随机二进制序列和正弦信号级联的相位调制对光谱展宽和受激布里渊散射效应抑制的影响，搭建了级联相位调制的高功率窄线宽光纤激光器，采用四级功率放大结构，在46 GHz均方根线宽下，实现了4.93 kW激光输出，中心波长为1067.5 nm，斜率效率为78%，光束质量为M~2＜1.2。

Objective Highpower narrowlinewidth fiber lasers are widely used in coherent synthesis and spectral synthesis; however, their power expansion is limited owing to stimulated Brillouin scattering. Common methods for inhibiting stimulated Brillouin scattering include the design and fabrication of stimulated Brillouin scattering suppression fibers and changing the temperature field and stress field distributions of the fibers. However, these methods entail complicated processing and can easily produce noise. In recent years, phase modulation of the light field has become the main method for suppressing stimulated Brillouin scattering. In the linewidth range of 50 GHz, singlestage phase modulation has a limited threshold boost for stimulated Brillouin scattering. In this study, we report a highpower narrowlinewidth fiber laser based on a cascaded pseudorandom binary sequence and sinusoidal phase modulation. The proposed method is expected to contribute to the power scaling amplification of narrowlinewidth fiber lasers in the 50-GHz linewidth range. Methods In this study, the appropriate pseudorandom binary sequence phase modulation parameters and lowpassfilter cutoff frequency are selected so that the unit spectral linewidth has the greatest suppression of stimulated Brillouin scattering. The effects of the modulation frequency and depth of sinusoidal phase modulation on the laser spectrum are studied. By changing the modulation frequency and depth, a spectral form with a fundamental frequency as high as the sideband of the +/- 1 level is obtained. After cascading the pseudorandom binary sequence and sinusoidal phase modulation, the spectrum shows a nearflattop morphology, which exhibits good stimulated Brillouin scattering suppression. According to the theoretical research results, a highpower narrowlinewidth fiber laser based on cascaded phase modulation is constructed, and the output powers and stimulated Brillouin scattering thresholds are compared at root mean square (RMS) linewidths of 20 GHz and 46 GHz. Results and Discussions Based on previous research, when the pseudorandom binary sequence phase modulation depth is 0.55 pi and the ratio of filter cutoff frequency to modulation frequency is 0.53, the modulation spectrum exhibits a nearflattop morphology (Fig. 2). According to theoretical research, the depth of sinusoidal modulation influences the number of spectral lines and the relative intensity of spectral lines, and the results are shown in Fig. 3. As the modulation depth increases, the number of spectral lines increases and the relative intensity of the spectral lines also changes. When the modulation frequency is reduced, the spectral line spacing and spectral linewidth are also significantly reduced. When the sinusoidal modulation frequency is 9.7 GHz and the modulation amplitude is 0.458 pi, the modulation spectrum has three single frequencies (Fig. 4). After cascading the pseudorandom binary sequence and sinusoidal phase modulation, the flatter spectral morphology than that from singlestage pseudorandom binary phase modulation is obtained, and the stimulated Brillouin scattering suppression is better. Based on the above research, a narrowlinewidth laser is built, and the output power and backward transmission power at RMS linewidths of 20 GHz and 46 GHz are monitored in the experiment (Fig. 7). When the RMS linewidth is 20 GHz and the output power is 2.2 kW, the backward power increases exponentially. When the RMS linewidth is 46 GHz,the output power is close to the SBS threshold. Because the stimulated Brillouin scattering phenomenon is not observed in the experiment, the power is increased to 4.93 kW, yielding a stimulated Brillouin scattering threshold enhancement factor of similar to 328, a system slope efficiency of 78%, and a beam quality factor (M-2) below 1.2. Conclusions In this study, the physical mechanism by which the cascaded pseudorandom binary sequence and sinusoidal phase modulation is used to broaden the laser spectrum to suppress stimulated Brillouin scattering is investigated. The effects of pseudorandom binary sequence modulation frequency and mode length on the spectrum are theoretically studied. Under the optimal ratio of the filter cutoff frequency to the pseudorandom binary sequence modulation frequency, the unit linewidth well suppresses stimulated Brillouin scattering. Through theoretical simulations, the influence of the modulation depth and modulation frequency of the sinusoidal signal on the laser spectrum is obtained. Based on theoretical guidance, a narrowlinewidth singlefiber laser based on cascaded phase modulation is built for the experiment. The cascaded pseudorandom binary sequence and sinusoidal phase modulation is used to widen the seed source spectrum. Compared with the stimulated Brillouin scattering thresholds and output powers under different RMS linewidths, the output power finally reaches 4.93 kW after amplification by the fourstage optical fiber when the RMS linewidth of the seed source is 46 GHz. The system slope efficiency is 78% and the beam quality factor M-2 is below 1.2

高功率窄线宽全光纤激光器具有GHz量级的光谱线宽和近衍射极限的光束质量,能通过大规模阵列组束实现激光光谱合成或相干合成,进而获得高亮度激光光源.窄线宽全光纤激光器功率提升的主要限制因素是高功率光纤放大器中的非线性效应[受激布里渊散射(SBS)和受激拉曼散射(SRS)等]和热致模式不稳定(TMI)效应.在数十GHz量级的光谱线宽下,有效提升非线性效应阈值(特别是SBS阈值)和TMI阈值是现阶段的研究重点.

Objective Semiconductor lasers are highly efficiency and have a small divergence angle, narrow pulse width, and good durability. They are widely used in material processing, industrial manufacturing, laser lighting, lidar, and laser communication. However, the output spot of the traditional edge-emitting semiconductor laser is elliptical and an additional beam shaping system is required. Further, it is sensitive to temperature change because the temperature drift coefficient at the central wavelength is 0. 3 nm/degrees C. Therefore, for a wide temperature range and large temperature differences between day and night, an additional temperature control system is required, which increases the volume, cost, and complexity of the laser. Recently, vertical-cavity surface-emitting lasers (VCSELs) have been used increasingly as semiconductor laser pump sources. Compared with traditional edge-emitting semiconductor lasers, VCSELs have circular output spots with a small divergence angle, good beam quality, small temperature drift coefficient, high reliability, and low cost. A VCSEL chip contains hundreds or thousands of units in the two-dimensional (2D) array distribution. Its high-power output of hundreds of watts or even kilowatts can be realized through the 2D array arrangement. Therefore, it is a suitable pump source for compact high-power solid-state lasers. In this paper, we report a laser with a VCSEL array as the pump source. The laser has the advantages of high beam quality, small volume, compact structure, and insensitivity to temperature change. It can be used under large day-to-night temperature differences as well as rapid temperature changes. Additionally, it serves as an emission light source for applications in space. Methods The laser uses an 808-nm VCSEL array as the pump source to pump Nd YAG crystal via end pumping. However, directly using it to pump the Nd: YAG crystal will lead to low power density and low pump efficiency because the VCSEL array is composed of many units and has a large luminous area. Therefore, collimating and shaping the output laser of the VCSEL array is fundamental. To shape the output laser of each unit in the VCSEL array, we employ a 2D microlens array with the same distribution as that of VCSEL. The shaped VCSEL pump light is coupled to the crystal with a focusing lens. The doping concentration (atomic fraction) of Nd YAG crystal is 0.5 yo, and its size is 3 mm X3 mm X 15 mm. The pumping side of the crystal is coated with 1064 nm high-reflection film and 808 nm high-transmission film. The output side is coated with 1064 nm and 808 nm high-transmission films. The electro-optic Q-switched module consists of a thin-film polarizer, KTP (KTiOPO4) crystal, and quarter-wave plate. It adopts a voltage-increased electro-optic Q-switched method and is driven by a high-voltage signal to realize the on-and-off switch. A flat mirror with transmissivity of 40 yo is used for output coupling, which forms a laser resonator with the gain crystal pumping side to realize the normal operation of the laser. The total length of the laser is 120 mm. Results and Discussions At a repetition frequency of 100 Hz, when the VCSEL pump energy is 28.25 mJ (working current is 150 A), the static output energy and dynamic output energy are 7.96 mJ and 5.36 mJ, respectively. The ratio between dynamic output energy and static output energy for Q switching is 67. 3Y0, and the optical-optical conversion efficiency is 18.9 yo (Fig. 6). Furthermore, the full width at half maximum of the output laser is 4.16 ns (Fig. 7) and the peak power is 1.29 MW. The beam quality factor along the two directions is M-x(2) =1.409 and M-y(2) =1.531 (Fig. 9). In the temperature range of 10-37 degrees C, the minimum and maximum output energies are 5. 24 mJ and 5. 58 mJ, respectively. Conclusions In this paper, we propose a compact solid-state laser with a small volume and large operating temperature range. The pump module consists of VCSEL and microlens arrays, and the VCSEL output laser is shaped using the microlens array. The Nd YAG crystal is pumped via end-pumping. Through the electro-optic Q-switching method, the laser is obtained with a pulse width of 4.16 ns, output energy of 5.36 mJ, and beam quality factors of M-2(x) =1.409 and M-y(2) = 1. 531. With the advantages of good beam quality, small volume, compact structure, and insensitivity to temperature change, the laser proves efficient under large day-to -night temperature differences and rapid temperature changes and can further be used as an emission laser source for application in space.

陆地生态系统碳监测卫星多波束激光雷达用于森林碳汇遥测,通过计算激光到达树冠和地面的时间差获取高精度的植被高度.激光器作为多波束激光雷达的发射光源,是其核心和关键部件.激光雷达对光源的需求是高光束品质、高脉冲重复频率的大能量纳秒脉冲激光.激光器采用主振荡功率放大的技术路线,振荡级为正交双Porro被动调Q超稳谐振腔构型,输出重复频率40Hz、脉冲宽度约4ns、单脉冲能量约2mJ的单频脉冲激光;放大级采用板条放大技术,获得单脉冲能量75mJ、光束品质因子M2优于1.5的激光输出,达到雷达所需光源指标要求,证明该激光器设计合理,可作为高重频对地遥感类激光光源的设计参考.