High-power Solid-state Lasers Research Articles

Efficient high-power diffraction-limited fiber laser with a record low quantum defect of 1.7%

In this work, we demonstrate an approach to potentially lower the quantum defect to ∼1% without significant compromise of efficiency. In a first demonstration, a diffraction-limited ∼154 W laser emitting at ∼993 nm with negligible amplified spontaneous emission, pumped at ∼976 nm, was achieved with a slope efficiency of ∼75% vs the launched pump power. The laser quantum defect is a record low of 1.7% for high-power (>100 W) solid-state lasers to the best of our knowledge. The output is only limited by the available pump power.

1.4 W Passively Q-Switched Mode-Locked Tm:CALGO Laser with a MoS2 Saturable Absorber

The passively Q-switched mode-locked (QML) operation of a Tm:CaGdAlO4 (Tm:CALGO) bulk laser pumped by a wavelength-tunable Ti:sapphire oscillator using molybdenum disulfide (MoS2) as a saturable absorber was demonstrated. By using an output coupler with 3% transmittance, Q-switched mode-locked operation can be achieved with 3.56 W absorbed pump power. At a pump power of 6.77 W, laser pulses with the maximum average power of 1.44 W were obtained, corresponding to a slope efficiency of 21.3%. The laser delivered pulses centered at 1927 nm with a repetition frequency of 131.6 MHz. The experimental results confirm the promising application of the MoS2 in high-power Q-switched mode-locked solid-state lasers at 2 µm.

Engineering the meta-phosphate BaO–Al2O3–P2O5 glass network for high average power (HAP) laser applications: Systematic composition modifications and SiO2 integration

The metaphosphate glasses are the preferred gain media for high-power solid-state laser applications. In the context of solid-state glass lasers, the main challenge to attain high average power (HAP) is to govern excessive thermal loading during operation. This work focuses on addressing thermal loading issues through improving thermal and mechanical properties of the meta-phosphate BaO–Al2O3–P2O5 laser glass system by engineering its molecular structure through systematic composition modifications with SiO2 incorporation. FTIR, Raman and 27Al MAS-NMR spectroscopy indicate stronger P–O–P bridges with decreasing glass basicity and increasing [AlO4] formations beyond 12.5 mol% Al2O3. The O/P ratio increases from 3.05 to 3.43 with up to 20 mol% SiO2 in Series-A and from 3.13 to 3.49 with up to 15 mol% SiO2 in Series-B, altering the Al coordination number from 6 to 4 to maintain the glass network charge balance. Increased [AlO4] formation raises Young's modulus from 61 GPa to 73 GPa and decreases Poisson's ratio from 0.30 to 0.24. These changes enhance fracture toughness and reduce CTE. Further, SiO2 inclusion enhances thermal conductivity by increasing glass network compactness and rigidity. These modifications highlight the improved thermo-mechanical properties of the SiO2-modified Series-B glasses. Yb3+ emission cross-section rises from 0.495 × 10−20 cm2 in ABSP-A1 glass to 0.502 × 10−20 cm2 in ABSP-B1 with increased [AlO4] formation. More AlPO4-like units in ABSP-B1 increase average glass phonon energy, reducing Yb3+ fluorescence lifetime from 1062 μs to 945 μs, whereas SiO2 addition boosts Yb3+ fluorescence lifetime again. Lower OH− content further extends Yb3+ fluorescence lifetime in Series-B glasses with higher SiO2 content. This study underscores the intricate relationship between glass molecular structure and thermal, mechanical, and spectroscopic properties, advancing high-power silico-phosphate laser glass development.

Analysis and optimization of repetitive positioning precision for kinematic couplings of opto-mechanical components considering uncertainty

Kinematic coupling, as an efficient form of connection, is frequently employed for the repeated assembly and accurate positioning of replaceable opto-mechanical assemblies within high-power solid-state laser systems. During the kinematic coupling process, uncertainties in the mechanical behavior within the contact region often hinder the attainment of consistent positioning precision, potentially leading to an inability to meet operational requirements. This study aims to enhance the repetitive positioning precision of kinematic couplings. A predictive model for repetitive positioning precision is established, accounting for uncertainties in contact region forces. Based on this model, an optimization design of kinematic couplings is conducted to mitigate these challenges. Initially, accounting for uncertainties in mechanical parameters within the contact region, we formulate a static analysis computational model to elucidate the probabilistic distribution of these parameters. Subsequently, employing Hertz contact theory and Holm-Archard wear theory, we quantify the elastic deformation and equivalent wear for each contact region through the calculation of normal pressures. Building upon this foundation, we establish a predictive model for repetitive positioning precision. Finally, optimization design is carried out on the friction coefficient of contact surfaces and the structural dimensions of positioning elements. The proposed optimization design is validated through experimental verification. The findings demonstrate that optimization of structural dimensions and contact surface friction coefficients resulted in enhanced repetitive positioning precision of 35.9 %, effectively ameliorating the assembly quality. This study contributes a quantifiable analytical approach to the prediction and optimization design of repetitive positioning precision in kinematic couplings.

Multi-mode stable, high peak power Nd:YAG laser device for laser cleaning

High average power and peak power solid-state lasers are of great interest in the field of laser cleaning. In this research, a high peak power laser with over 400 W average power using a multi-mode stable resonator in a diode-pumped Nd:YAG master oscillator power amplifier has been demonstrated. A maximum peak power over 1.08 MW was achieved at a repetition frequency of 5 kHz. Delivery fiber with a 400 µm core diameter was utilized for flexible laser transmission. A prototype of the laser cleaning system was developed and inspiring application effects for paint and mold cleaning were achieved.

Use of the Laser Fragmentation Method in the Extraction of LFCM from the Shelter

The Project to transform the Shelter into an environmentally safe system has achieved a significant milestone in the process of transitioning Chornobyl NPP Unit 4 to a safe environmental state. However, the program does not include the measures for long-term safe management of the nuclear stockpile at Chornobyl NPP Unit 4 that are essential. A considerable amount of fuel, approximately 200 tons, has been mixed with reactor debris and structural components, resulting in the formation of fuel-containing materials spanning hundreds of cubic meters. These fuel-containing materials are located in the lower levels of Chornobyl NPP Unit 4.
 Given the degradation and natural deterioration of fuel-containing materials leading to generation of radioactive aerosols, as well as recent changes in neutron flux density observed after the installation of the New Safe Confinement, there is an urgent need to enhance the development and implementation of appropriate technology. One promising approach is application of the dry fragmentation technology, which uses a high-power solid-state laser developed at the Fraunhofer IWS laboratory in cooperation with the Institute for Safety Problems of Nuclear Power Plants NAS of Ukraine and Plejades GmbH. This technology offers advantages such as minimizing the dynamic and static loads on local structures, efficient energy transfer (heat), and reducing dust formation.
 This article presents the main aspects of the laser fragmentation method of LFCM. The article describes the details of the controlled destruction technology of thermally stressed material, developed as a result of tests with simulated material at the Fraunhofer IWS laboratory. The work is focused on the measures required for implementing the dry fragmentation technology at the Shelter. It presents pre-conceptual approaches for retrieval and handling of fuel-containing materials located in the lower floors of Chornobyl NPP. The article outlines an approach for accessing fuel-containing materials, a strategy for their fragmentation, subsequent packaging, and safe storage within the Chornobyl NPP until final disposal. Additionally, the creation of a tool system and means of delivery are also described.

Creation of High-Power Technological Nanosecond Frequency-Pulse Solid-State Lasers: Problems and Solutions

A review analysis of the problematic aspects of creating high-power nanosecond frequency-pulse solid-state lasers for use in various technological fields, including the electronics industry, has been carried out. Considered installations with various pumping methods (lamp and diode) in the frequency (about 100 Hz) of generation in the micron region of the infrared range. The possibilities of increasing the energy potential of influencing pulses in master oscillator-amplifier circuits, including two-pass amplification, are analyzed. Discussed possibilities and prospects for the use of lasers with active elements (AEs) on glass, as well as the synthesis of large-sized garnet single crystals with an admixture of rare earth elements and opticalceramics for the production of AEs.

Creation of High-Power Technological Nanosecond Frequency-Pulse Solid-State Lasers: Problems and Solutions

Creation of High-Power Technological Nanosecond Frequency-Pulse Solid-State Lasers: Problems and Solutions

Editorial: Advanced high power solid-state laser technology

Editorial: Advanced high power solid-state laser technology

Effect of introducing KNO3 on the preparation of athermal fluorophosphate glass and investigation on its thermo-optical property

The effects of introducing some amount of KNO3 into the raw materials on preparation of fluorophosphate glass are investigated in terms of UV–vis transmittance, absorption coefficient and change of refractive index. As the content of KNO3 reaches 50%, the UV absorption coefficient of the optimized fluorophosphate glass reaches the minimum due to absence of microcrystals in the produced glass. The Schott's Sellmeier dispersion formula and Ghosh's two-polar wavelength-dependent Sellmeier equation were both used to calculate dispersion constants of the optimized fluorophosphate glass. The optimized fluorophosphate glass maintains special characteristics of negative temperature coefficient of refractive index and near-zero thermo-optical coefficient. The lower absorption both in UV and near-infrared (NIR) helps to improve its laser-induced damage resistance. The athermal fluorophosphate glass shows great potential for compensation of thermal-induced distortion in high-power solid-state lasers and high-resolution optical systems.

High-power and efficient vortex Nd:YVO4 laser using annular pumping

Optical vortex lasers that carry orbital angular momentum are of great significance for many applications. A high-power and efficient continuous-wave vortex Nd:YVO4 laser at 1064 nm was demonstrated with annular pumping based on an axicon. The high-quality LG01 vortex beams with maximum output power up to 6.25 W was achieved under the absorbed pump power of 14.4 W, corresponding to an optical conversion efficiency of 43.4% and a slope efficiency of 44.8%, respectively. Controlling the wavefront handedness of the LG01 beam was simply achieved by carefully adjusting the output coupler and the window inserted in the resonator. This study shows that annular pumping based on an axicon would have great potential in the development of high-power vortex solid-state lasers with simple and compact resonator structure.

Monolithic 591-nm laser with cooperative multiphonon-coupling and nonlinear frequency-doubling.

Stable and miniaturized orange lasers at 591 nm are in urgent demand for ophthalmology and dermatological treatment. However, at present, traditional dye lasers and nonlinear sum-frequency lasers are limited by their complex setup and high cost, whereas semiconductor laser diodes (LDs) emitting in the yellow-orange range suffer from low output power. Here, we propose a new, to the best of our knowledge, route to create self-frequency-doubling (SFD) orange laser with a combination of multiphonon-assisted lasing and nonlinear frequency-doubling in one crystal. Using Yb3+-doped YCa4O(BO3)3 (Yb:YCOB) crystal, we first realize a widely tunable laser beyond the fluorescence spectrum in the wavelength range of 1175-1248 nm. Then, by selecting the laser polarization and crystal angle to satisfy phase-matching conditions, we obtained a directly diode-pumped orange laser at 591.8 nm with 3.07-W output power and an optical-to-optical conversion efficiency of 13%. This work represents a new step forward for portable high-power solid-state orange lasers and provides an intriguing platform for electron-phonon coupled lasing.

Development of a 2 μm Solid-State Laser for Lidar in the Past Decade.

The 2 μm wavelength belongs to the eye-safe band and has a wide range of applications in the fields of lidar, biomedicine, and materials processing. With the rapid development of military, wind power, sensing, and other industries, new requirements for 2 μm solid-state laser light sources have emerged, especially in the field of lidar. This paper focuses on the research progress of 2 μm solid-state lasers for lidar over the past decade. The technology and performance of 2 μm pulsed single longitudinal mode solid-state lasers, 2 μm seed solid-state lasers, and 2 μm high power solid-state lasers are, respectively, summarized and analyzed. This paper also introduces the properties of gain media commonly used in the 2 μm band, the construction method of new bonded crystals, and the fabrication method of saturable absorbers. Finally, the future prospects of 2 μm solid-state lasers for lidar are presented.

Progress of Edge-Emitting Diode Lasers Based on Coupled-Waveguide Concept.

Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power solid-state and fiber lasers. In this work, an approach for optical mode engineering in planar waveguides is investigated. The approach referred to as Coupled Large Optical Cavity (CLOC) is based on the resonant optical coupling between waveguides and allows the selection of high-order modes. The state-of-art of the CLOC operation is reviewed and discussed. We apply the CLOC concept in our waveguide design strategy. The results in both numerical simulation and experiment show that the CLOC approach can be considered a simple and cost-efficient solution for improving diode laser performance.

Stimulated Emission Cross-Section Measurement for Laser Crystals of High-Power Solid-State Lasers Using Relaxation Oscillation Frequency

We demonstrate a new method for measuring the stimulated emission cross-section (σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>s</i></sub> ) of laser crystals for high-power solid-state lasers at working state using the relaxation oscillation frequency (ROF). The method is implemented by measuring the ROF of the laser together with making the relation curve between the ROF and σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>s</i></sub> of the laser. The stimulated emission cross-section of the laser crystal can be obtained when the ROF in the relation curve equals to that of the measured value. Employing the method, the actual σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>s</i></sub> of the Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystals with doping concentrations and pumping powers of 0.2 at.% and 51.5 W at 808 nm, 0.8 at.% and 80 W at 888 nm, and 0.8 at.% and 113 W at 888 nm are measured upon considering the influence of concentration quenching and energy transfer upconversion of the lasers. The measured results are 23.34 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-19</sup> , 23.77 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-19</sup> , and 23.42 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The results are further compared and analysed with considering the temperature gradient of the laser crystals. It is found that the anomalous temperature gradient of the laser crystal at working state can induce an inhomogeneous gain spectral broadening, which can severely impact σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>s</i></sub> of the laser crystal.

Significant enhancement of luminescence properties of YAG:Ce ceramics by differential grain sizes control

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al2O3–YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al2O3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting.

Characteristics and Recent Development of Fluoride Magneto-Optical Crystals

Magneto-optical materials are the fundamental component of Faraday isolators; therefore, they are significantly important for solid-state laser systems. Fluoride magneto-optical crystals such as CeF3, KTb3F10 and LiTbF4 exhibit advantages of wide transmittance range, high optical homogeneity, smaller thermal lensing and weaker thermal induced depolarization effect, and thus are promising candidates for Faraday isolators in high-power solid-state lasers. Recent progress in crystal growth and characterizations of these fluoride magneto-optical crystals are introduced. Possible applications of Faraday isolators based on various fluoride crystals are discussed, especially for solid-state lasers in the ultraviolet (UV) or infrared (IR) spectral region.

Исследование однородности распределения накачки в активном элементе в виде стержня мощных квантронов с диодной накачкой

Experimental investigations and calculations of various optical schemes of high-power DPSS and solid-state lasers with cylindrical active elements and transverse pumping by laser diode arrays are presented. Numerical simulations were used to solve hydrodynamic problems and problems of geometric optics for DPSS with rod active elements pumping by quasi-continuous laser diode arrays. The dependencies of the uniformity of active element illumination on the geometry of the optical scheme were studied, as well as the influence of the uniformity of coolant flows over different pump arms on the uniformity of the luminescence distribution pro-file from the end of the active element. An optical pumping scheme for active element of a high-power DPSS with an optimal geometry is proposed and implemented.

(Na0.74 Ag1.26 )BaSnS4 : A New AgGaS2 -Type Nonlinear Optical Sulfide with a Wide Band Gap and High Laser Induced Damage Threshold.

The development of high-power solid-state lasers is in urgent need of infrared (IR) nonlinear optical (NLO) materials with wide band gaps and high laser-induced damage thresholds (LIDTs). Herein, a new compressed chalcopyrite-like IR NLO crystal (Na0.74 Ag1.26 )BaSnS4 was successfully synthesized using a facile high-temperature solid-state method. Its structure can be considered as a variant of chalcopyrite AgGaS2 (AGS)-type ones. It features a three-dimensional framework constructed by corner-sharing {[(Na/Ag)S4 ]7- }∞ layers and isolated SnS4 tetrahedra with negative cavities occupied by counter ion Ba2+ . (Na0.74 Ag1.26 )BaSnS4 exhibits phase-matchable moderate SHG response (0.31 × AGS), wide band gap (3.70 eV), and high LIDT (6.44 × AGS). Theoretical calculations reveal that the NLO response of (Na0.74 Ag1.26 )BaSnS4 is mainly originated from the synergetic effects of AgS4 and SnS4 tetrahedra, and the inclusion of alkaline and alkaline earth metals is responsible for the wide band gap and high LIDT. Moreover, the discovery of this chalcopyrite-like compound will provide a feasible design strategy for the exploration of new promising IR NLO materials.

Accurate thermal stress induced birefringence measurement of laser crystal with cavity ring-down technique

One of the main sources of beam quality deterioration encountered in high-power diode-pumped solid-state lasers is the thermal stress induced birefringence. Cavity ring-down (CRD) technique is applied to the accurate measurement of thermal stress induced birefringence of laser crystal under pump diode laser illumination. Measurements of the pump laser illumination induced temperature profile and thermal stress induced birefringence retardance distribution in the laser crystal are performed and compared to numerical calculations to determine the absorption and thermal diffusivity of the laser crystal and further the relevant stress-optical constant. The experimental results demonstrated that CRD is a highly sensitive and accurate technique to measure the thermal stress induced birefringence and relevant stress-optical constant of laser crystals, which is helpful for the evaluation and optimization of the performance of high-power laser systems.