Abstract We show a high-slope-efficiency Ho:CaYAlO 4 laser using the conventional water-cooling method. Under an L-shaped laser resonator cavity with an overlapping efficiency greater than 98%, a maximum output power of 18.64 W at 2081 nm was achieved when the absorbed pump power was 26.83 W. By linear fitting, the slope efficiency relative to the absorbed pump power is 90.6%. Under the maximum output power, the beam quality factor is lower than 1.25 and the root-mean-square stability is about 0.42%. In addition, we validated the output performances of the laser in acousto-optic Q -switched mode under the high-slope-efficiency condition. At a pulse repetition rate of 10 kHz, the maximum average output power of 18.26 W and the narrowest pulse width of 40.1 ns were achieved, corresponding to a pulse energy, peak power and slope efficiency of 1.83 mJ, 45.54 kW and 87.7%, respectively. To the best of our knowledge, this laser may have the highest slope efficiency for a Ho-doped solid-state laser using conventional water-cooling.
We propose a spatially resolved B-integral measurement method for high-power laser drivers based on off-axis aberration characterization. Theoretical analysis confirms the feasibility and high precision of this approach, in which coma-shaped intensity modulation is intentionally introduced into the laser system, imprinting nonlinear phase modulation with a corresponding aberration profile. The B-integral is then extracted by measuring the coma component of the output beam using a Shack-Hartmann sensor. The experimental results demonstrate a 5.8% deviation between the measured and simulated B-integral values for coma aberration, showing that the proposed method significantly outperforms the defocus-based measurement method (67.4% error) in terms of error reduction. This method does not require modifications to the laser setup, offers a single-shot measurement capability and achieves high accuracy and excellent repeatability. The direct quantification of wavefront phase distortions provides a practical solution for nonlinear phase modulation diagnostics in high-power laser systems.
We present a high-brightness, nanosecond pulsed blue laser source at 476.8 nm through efficient quadruple-harmonic generation from a thulium-doped yttrium lithium fluoride (Tm:YLF) master oscillator power amplifier operating at 1.9 mu m. The fundamental-frequency stage produces 42 mJ pulses at 1907.3 nm with a narrow linewidth of 0.19 nm at 1 kHz. Through cascade second-harmonic generation using low-walk-off lithium triborate crystals, we achieve 10.52 mJ blue laser pulses with 16.1 ns duration, corresponding to a peak power of 0.65 MW and exhibiting excellent energy stability of 0.47%. The system maintains exceptional beam quality (M-x(2) = 1.46, M-y(2) = 1.27) at maximum output power, attributed to the negative thermal-optical properties of the Tm:YLF crystal, end-pumped amplification architecture and optimized nonlinear conversion. This work demonstrates a compact and efficient route to high-brightness (similar to 2.49 GW.cm(-2).sr(-1)) pulsed blue laser emission, which is particularly suitable for advanced marine scientific applications including underwater LiDAR and communication systems.
A fiber-based route to mid-infrared nanosecond pulse laser generation in gas-filled hollow-core anti-resonant fiber at 4.3 mu m with 10-W-level average power is demonstrated. The demonstration experiments, harnessing a single pump pulse with 37 ns duration and 125 W output power at 2 mu m in a CO2-filled large-mode-field hollow-core anti-resonant fiber, produce nanosecond pulses centered at the 4.3 mu m band with the output power of 10.27 W, with a pulse width of 29 ns and a repetition rate of 10 MHz. Efficient high-power mid-infrared laser generation is realized by detuning the pump wavelength from the CO2 molecular absorption peak, leading to mitigating the gain saturation issue in the CO2-filled hollow-core anti-resonant fiber laser under high-power pumping. To the best of our knowledge, this represents the highest power reported for CO2-filled hollow-core fiber nanosecond pulse laser sources to date, demonstrating a 34-fold power improvement over previous works.
Spectral broadening in guided-wave optics, an effect intrinsic to the interplay of dispersion and nonlinearity, presents a major obstacle to achieving the high spectral purity required for applications in nonlinear frequency conversion and precision spectroscopy. This effect is especially detrimental in high-power cascaded Raman fibre lasers (CRFLs). Leveraging a concept analogous to wavefront shaping but implemented passively, we introduce and validate a novel architecture for CRFLs incorporating random fibre grating-assisted spectral tailoring. A theoretical model is developed to show that the randomized reflectance profile of the grating induces wavelength-selective feedback, promoting intracavity mode competition and noise suppression through enhanced coherent enhancement of selected spectral components. Experimentally, we demonstrate a maximum output power exceeding 1 kW at 1185 nm from the cascaded Raman fibre oscillator. The random grating provides enhanced spectral control, achieving a 3-dB linewidth of approximately 1.0 nm. Notably, it also significantly suppresses the spectral wings, reducing the 10- and 30-dB linewidths to 2.9 and 9.5 nm, respectively. This work represents the first implementation of built-in passive spectral tailoring in an all-fibre nonlinear dynamical system, offering insights into the control of complex light fields in both temporal and frequency domains throughout cascaded nonlinear processes.
We demonstrate that tailoring the laser-target interaction at the PW-class VEGA-3 facility (by controlling the focusing conditions, pulse duration, chirp sign and solid-target properties) enables the enhancement of ion flux, divergence and cutoff energy for high-energy-density physics experiments. The existence of optimal pulse duration, focusing conditions, target thickness and target material is experimentally demonstrated. We further show that a reduction in ion acceleration efficiency under best-compression conditions leads to delayed relative depletion of the hydrogen population compared to carbon ions, accompanied by a decrease in both ion flux and cutoff energy. For metallic targets, scintillator detectors reveal a more divergent and deflected proton beam than that produced from thick plastic targets. The product of the magnetic field strength and the interaction length acting on the ions is estimated to reach up to 400 MG mu m, resulting in a ring-like spatial distribution of protons generated from aluminum and copper targets.
We have investigated the equation of state (EoS) of hexagonal boron nitride (h-BN) under extreme conditions using the Prague Asterix Laser System facility. The experiment employed a 438 nm wavelength laser pulse with a pulse duration of approximately 350 ps delivering up to 200 J of energy. A phase plate ensured a uniform flat-top intensity profile with a diameter of approximately 400 mu m. Shock wave velocities were simultaneously determined in BN and in a reference material from time- and space-resolved self-emission measurements using a streaked optical pyrometer. The EoS of BN was determined by comparing its response to that of the reference material. We achieved high compression of BN (up to 9 Mbar). By expanding the experimental dataset on the EoS of h-BN, this study contributes to a more comprehensive understanding of behavior of this material under extreme conditions, supporting advancements in fusion energy research, high-energy-density physics and possibly next-generation inertial confinement fusion target designs.
In this work, we experimentally demonstrate a high-power supercontinuum (SC) that covers from visible to mid-infrared (MIR) in a GeO2-core fiber (GCF) bundle via incoherent beam combination. In the experiment, the SC generation in a single GCF was initially explored, and an SC spanning from visible to MIR regions was obtained, with average power of less than 10 W. To increase the output power, we fabricated a 3 & times;1 high-power GCF-based tapered fiber bundle, incoherently combining three channels of the previously mentioned replicas. This yielded a broadband SC spectrum with a maximum average power of 23.1 W and a spectral bandwidth covering 0.73-3.1 mu m. The obtained spectrum power fluctuation was measured over 1 hour, showing a root mean square value of 0.7%. To the best of our knowledge, this represents the highest power SC from visible to MIR regions obtained in GCFs pumped by 1.55 mu m high-power pulses.
We present the characterization of intensity distributions and the beam wavefront along the caustic of an iodine photodissociation laser beam at the Prague Asterix Laser System. Its $700\;\mathrm{J},300\;\mathrm{ps}$ laser pulse was attenuated by neutral-density optical filters and focused by an $f/2.2$ aspherical lens. In multiple planes at and around the focus position ( $\pm 7 imes \mathrm{Rayleigh}\kern0.17em \mathrm{length}$ ), we measured fluence distributions by far-field imaging with a nonlinearity-corrected camera. We used these measurements to retrieve the beam wavefront by a phase retrieval algorithm with dynamic input-output mixing. We then propagated the beam to the focus position and to the lens position. The calculated peak intensity at the focus position was $7.9 imes {10}<^>{18}\;\mathrm{W}/{\mathrm{cm}}<^>2$ , and $300\;\mathrm{J}$ (43% of the pulse energy) was contained within the intensity region above the relativistic intensity threshold of $0.8 imes {10}<^>{18}\;\mathrm{W}/{\mathrm{cm}}<^>2@1315.2\;\mathrm{nm}$ .
We report a high-power broadband flat supercontinuum laser system based on a large-mode-area (LMA) low-loss fluorotellurite fiber cascaded with an LMA chalcogenide fiber. To effectively expand the coverage of the mid-infrared supercontinuum spectrum and enhance its flatness, a novel femtosecond Raman-soliton laser with high peak power is used as the pump source. When pumping the fluorotellurite fiber, a supercontinuum extended to 4.2 mu m can be obtained, with an output power of 8.12 W. Subsequently, we further pumped an LMA As2S3 fiber. At the maximum input power, the output power of the supercontinuum can reach 2.6 W, with the spectral edge extending to 5.7 mu m, a 10-dB bandwidth spanning 2-4.7 mu m and favorable power stability retained. To the best of our knowledge, this is the first laser system that uses a fluorotellurite fiber as a transition fiber and further cascades the chalcogenide fiber to generate mid- and long-wave infrared supercontinuum, achieving the highest output power of a mid- to long-wave infrared supercontinuum laser generated in As2S3 fiber reported to date.
LiGaS2 crystals are prospective media for optical parametric oscillators. In such systems efficiency and maximum power output are often limited by the laser-induced damage threshold (LIDT) of nonlinear crystals. In addition, most nonlinear crystals have a high refractive index and consequently large Fresnel losses, thus encouraging the use of antireflection coatings. However, antireflection coatings are known to compromise the LIDT. This work presents results of the LIDT testing of LiGaS2 nonlinear crystals in untreated, antireflection-coated and antireflection-microstructured variations. The tests were performed using a one-on-one method with pulsed lasers operating at 1.57, 2.09 and 2.5 μm wavelengths with pulse durations of 9, 149 and 12 ns, respectively. The paper covers damage site feature investigation and LIDT comparison of antireflection coating and antireflection microstructures. The key finding of the work is that antireflection microstructures can provide an increase in transmittance for both the pump and the signal, while maintaining a high LIDT.
High-energy nanosecond pulses at wavelengths beyond 2.5 mu m in the mid-infrared (mid-IR) region are of significant interest for applications such as polymer processing, minimally invasive surgery, laser ranging and infrared countermeasures. While rare-earth-doped fluoride fibers provide a compact and robust platform for mid-IR pulse generation, achieving millijoule (mJ)-level nanosecond pulses beyond 3 mu m remains challenging. In this work, we demonstrate high-energy nanosecond pulse generation at 3.17 mu m using a master oscillator power amplifier based on a 980 nm diode-pumped Er3+/Dy3+ co-doped fluoride fiber. Seeded by an actively Q-switched oscillator operating at a 1 kHz repetition rate, the system delivers 0.68 mJ of pulse energy with a pulse width of 132 ns and a peak power of 4.8 kW, while maintaining single-transverse-mode operation (M-2 = 1.2-1.3). To the best of our knowledge, this work represents the first report on mJ-level nanosecond pulse generation beyond 3 mu m from a fiber-based system.
Surface defects on fused silica optics significantly limit their laser-induced damage resistance under ultraviolet pulsed laser irradiation, yet quantitative correlations between defect parameters and damage thresholds remain scarce. This study is the first to perform multimodal detection and correlation analysis of laser-induced damage initiated at real defects on fused silica. Scratches were characterized by scattered light intensity, width and fluorescence intensity, and correlated with the damage-onset fluence (DOF). Results show trailing indent scratches (1.9-8.8 mu m wide) have DOFs of 1.27-13.2 J/cm(2), while plastic continuous scratches (0.4-5.8 mu m wide) exhibit higher DOFs of 12.3- 22.0 J/cm(2). Fluorescence intensity strongly negatively correlates with DOF (p < 0.001), as do scratch width and fluorescence intensity at alpha = 0.01 (p < 0.01). These findings establish scratch width and fluorescence intensity as quantitative damage precursors, advancing surface quality assessment for high-energy laser optics.
A spatiotemporal optical vortex (STOV) with transverse orbital angular momentum can induce some novel properties in high-energy-density physics. However, the current STOV pulse energy is limited to the mJ level, which greatly hinders the development of the research field of relativistic laser-matter interaction. Combined with the large-scale grating pair in high-peak-power laser facilities, a method for generating STOVs with ultra-high intensity of up to 1021 W/cm2 is proposed. The numerical simulation proves that a wave packet with 60 fs duration and 83 J energy can be generated in the far-field, maintaining an integral spatiotemporal vortex construction. Simultaneously, STOVs with 1.1 mJ single-pulse energy were obtained in a proof-of-principle experiment, and characterized by a home-made measuring device.
Deep learning (DL) has been applied to phase control in coherent beam combining (CBC) recently. However, existing DL-based approaches for filled-aperture CBC essentially convert the phase-locking path into tiled-aperture schemes. Consequently, common-path phase locking in DL-based filled-aperture CBC remains unrealized. Common-path refers to a phase-locking scheme in which the phase information is extracted from the combined beam after the same combining system. In this paper, a common-path phase-locking method is proposed. By exploiting the intrinsic nonuniformity, each laser source is effectively labeled, enabling a mapping between the combined speckle and the multi-source phase. A neural network is employed to reconstruct the phase. Simulations with 25-channel CBC demonstrate a phase-locking accuracy of up to lambda/39. Notably, it remains effective under dynamic phase disturbances. Our work presents a common-path phase-locking approach based on a neural network for filled-aperture CBC, which can offer a new solution for the field.
To mitigate inhomogeneous thermal and stress effects caused by multi-pulse accumulation in laser-material interactions, we propose an all-optical strategy to generate a structured beam, termed a 'drill-like laser', featuring a petal-shaped intensity profile with stochastic rotation by shot-to-shot control. The strategy involves generating collinear signal and idler pulses carrying conjugated orbital angular momenta via optical parametric amplification (OPA). The pulses then interfere with each other to form a beam with petal-shaped intensity structure, whose orientation is governed by their carrier-envelope phase (CEP) difference. The strategy is further implemented with a dual-stage OPA system pumped by an 800-Hz-30-fs-800-nm femtosecond laser, where the CEP difference is directly controlled by the pump CEP. Experimentally, a drill-like laser at 1.6 mu m is demonstrated with stochastic shot-to-shot intensity rotation, resulting from the shot-to-shot random fluctuation of the pump CEPs, which has been validated using dual-line pump-probe detection via sum-frequency generation. Crucially, since the interference arises from two beams with free-space eigenmodes, rather than angular-dispersion-based spatiotemporal coupling, the drill-like laser maintains high propagation stability and is scalable in power by conventional laser amplification, holding great potential for applications in precision laser processing and other high-field scenarios.
We present an experimental study on electron and X-ray generation from the interaction of a hundreds of TW femtosecond laser with microchannels. Leveraging the guiding effect of the channel structure on both the laser and electrons, a well-collimated electron beam is achieved, with a beam charge of 1.5 nC (>10 MeV), a slope temperature of 9.1 MeV and a nearly constant divergence angle (similar to 14 degrees) over a broad energy range (10-50 MeV). Meanwhile, we demonstrate a ring-shaped X-ray source generated through bremsstrahlung radiation mechanism from electrons collision with channel walls, exhibiting a characteristic energy of 90 keV and emittance of 0.8 mm mrad. Three-dimensional simulations elucidate the underlying acceleration dynamics. It is found that elongated channels facilitate the formation of well-collimated electron beams. These results establish the foundation for applications of channel guided electrons and secondary radiation sources and represent a key step toward the controlled manipulation of particle sources in laser-driven plasmas.
We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.
A high-power, efficient pulsed amplifier based on a laser diode end-pumped ytterbium-doped yttrium aluminum garnet (Yb:YAG) rod was demonstrated. The crystal’s reabsorption was effectively minimized by optimizing the amplifier’s parameters through numerical simulations, leading to a power extraction efficiency of up to 56%. A compensation method was applied to correct the beam distortion caused by thermally induced birefringence in the Yb:YAG rod. Furthermore, a remarkably low depolarization rate of 2.2% was achieved, along with an average power output of 483 W. The beam quality factor (M2) of the amplified signal was improved to below 1.3, following compensation of the thermally induced spherical aberration using a phase plate. To the best of our knowledge, this achievement represents the highest average power and efficiency for fundamental mode operation in an Yb:YAG rod amplifier at room temperature.
