We demonstrate a high-power InnoSlab amplifier based on a multi-segmented composite ytterbium-doped yttrium aluminum garnet (Yb:YAG) crystal. A systematic comparison was performed of the laser amplification output performance of multi-segmented and conventional Yb:YAG crystals to demonstrate the feasibility of using gain media with multiple doping concentrations in InnoSlab laser amplifiers. We achieved an amplified output of 245 W based on the multi-segmented composite Yb:YAG crystal InnoSlab amplifier, with a beam quality of M 2 = 1.21 & times; 1.25 and an optical-to-optical efficiency of 38.9%. Thanks to the unique doping structure of the composite crystal, compared to homogeneous dopant crystals, the average output power, optical-to-optical efficiency and beam quality were significantly improved. Exceptional output power stability with a root mean square fluctuation of 0.11% and pointing stability of approximately 7.5 mu rad were achieved.

We demonstrate a dispersion-engineered folded multi-pass cell (MPC) for few-cycle nonlinear pulse compression, delivering 10.7 fs pulses with 11 W average power at 200 kHz repetition rate, exhibiting a high throughput of 92% and a near-diffraction-limited beam quality of M2∼1.3. The beam path is folded by multiple reflections on additional plane mirrors, resulting in a footprint of 0.55 × 0.15 m2. The precise dispersion management is achieved by strategically replacing one of the plane folding mirrors with an off-the-shelf chirped mirror. The stable pulse propagation and self-phase-modulation (SPM)-dominated spectral broadening are maintained during the nonlinear process in the MPC, enabling efficient compression into the few-cycle regime without spectral broadening saturation.

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 the first experimental demonstration of directional and collimated electron acceleration in the direct laser acceleration regime using a relativistic hollow Laguerre-Gaussian (LG) laser. Electrons are confined within the hollow field distribution along the reflected laser direction, producing a collimated beam and overcoming the dispersed characteristic of Gaussian-laser-driven electrons. In particular, the left-circularly polarized LG laser generates a unique longitudinal resonant electric field on the axis, which, combined with transverse confinement, forms a stable acceleration structure. This leads to higher electron energies with improved stability and collimation compared with right-circularly polarized LG cases. The demonstrated LG-laser-driven collimating mechanism extends conventional direct laser acceleration into a stable and efficient regime, opening opportunities for particle collimation, high-flux particle sources, and coherent radiation generation in relativistic regimes.

We report a high-power, ultrafast coherent beam combination system featuring two InnoSlab CPAs based on Yb: YAG crystals. 306 W average power and 1.53 mJ pulse energy are delivered at 200 kHz, with a power fluctuation of 0.52% RMS. The combined beam quality is optimized from M2 = 1.24 × 1.41 to M2 = 1.1 × 1.18, due to the filtering effect of spatial mode. The combined beam is compressed to 460 fs by a grating compressor with close to the diffraction-limited spatial beam quality. Both excellent spatiotemporal performance and long-time stability are achieved, representing a novel, to the best of our knowledge, kilowatt-class average power amplifier which will greatly benefit the applications.

We systematically investigate second-harmonic generation (SHG) in a lithium triborate (LBO) crystal by a femtosecond laser system (1030 nm, 195 fs, 30 W) with particular emphasis on back-conversion phenomena. For a selected 5 mm thick crystal, an optimal conversion efficiency of 54% is achieved at 18 W input power with beam quality factor M2 of 1.275 (horizontal) and 1.173 (vertical). Beyond the saturation threshold where back-conversion initiates, spectral broadening, temporal compression and beam quality deterioration emerge, accompanied by decreasing conversion efficiency. Increasing the beam diameter or reducing the crystal length effectively mitigates back-conversion phenomena. These findings establish valuable guidelines for optimizing the performance of femtosecond visible laser sources.

Ytterbium-based ultrafast lasers facilitate efficient and power-scalable femtosecond lasers with state-of-the-art fiber, Innoslab, and thin-disk architectures. Among them, Innoslab amplifier distinguished themselves for their outstanding performance in single-pass gain and compactness [1], [2]. A hybrid cavity is typically employed in the Innoslab geometry as a cylindrical thermal lens was established in the gain medium. In the fast axis, a self-reproducing laser mode is realized at each roundtrip through two plane mirrors along with the thermal lensing effect of the crystal. In the slow axis, the beam is expanded to balance the power increase, keeping the optics safe and B-integral small. A tight overlap between successive passes is necessary to achieve enough extraction efficiency and suppress parasitic lasing also. Consequently, the output beam shows sidelobes in the slow axis due to the diffraction at the output port, which deteriorate the beam quality. Other effects such as amplified spontaneous emission (ASE) or slight self-lasing will further degrade the beam quality if not eliminated. In the conventional Innoslab amplifier, a spatial filter was routinely applied to improve the output beam quality in the slow axis. The loss-afflicted spatial filter also demands precise alignment.

We demonstrated a high average power dual-crystal Yb:CALGO regenerative amplifier(RA) operated in TEM00 mode. The dual-crystal configuration effectively mitigated thermal effects and enabled a continuous output power of 42.5 W at a pump power of 160 W with the central wavelength of 1054 nm. During regenerative amplification, an amplified output power of 38 W was obtained at repetition rates ranging from 50 to 200 kHz, the central wavelength of 1043 nm while a compressed pulse width of 290.8 fs. Benefiting from effective thermal management and the thermal insensitive cavity, a near-diffraction-limited beam quality was measured to be Mx2 = 1.11 and My2=1.11 at the highest output power.

We demonstrate a high energy nonlinear pulse compression scheme based on a hybrid bulk-air multi-pass cell (MPC), achieving a high-power ultrafast source with 45 fs pulse duration, 130 W average power at 200 kHz repetition rate, and near-diffraction-limited beam quality. The impact of air nonlinearity accumulation in the MPC on beam quality is investigated to maintain good beam quality at high pulse energy, which suggests the adoption of pre-chirped and circularly-polarized pulses can effectively improve the input pulse energy and suppress the spatial quality degradation. The nonlinear mode-matching is also adopted to minimize the impact of the self-focusing effect of solid-thin-plates on q-preserving propagation. Although both solid plates and air contribute to the spectral broadening, the hybrid MPC is still an all-solid-state configuration without a pressure-controlled cell, providing a compact and economical approach for the nonlinear pulse compression at several hundred microjoules (µJ) energy levels. To the best of our knowledge, this is the highest pulse energy from the solid-state MPC configuration.

Enhancing the flux, brightness, and density of energetic electron beams is crucial for applications such as ultrafast electron diffraction, fast ignition in confined fusion, and free-electron lasers. Laser Wakefield Acceleration (LWFA) has demonstrated potential for accelerating collimated electrons up to 10 Giga-electron volts in 'bubble-like' plasma channels. However, its reliance on the plasma environment constrains the enhancement of acceleration stability and gradients. In contrast, Direct Laser Acceleration (DLA) does not depend on plasma and can achieve efficient acceleration with traditional Gaussian lasers. Nonetheless, traditional DLA often results in uncertain and divergent electron beams due to the ponderomotive force of the Gaussian laser. To overcome these limitations, our proof-of-principle experiments achieved collimated acceleration using a left circularly polarized Laguerre Gaussian (LG) laser in a DLA mechanism. Studies revealed that a novel vacuum bubble field formed by the LG laser is critical in simultaneously concentrating and accelerating electrons. This vacuum bubble field mechanism integrates the advantages of both traditional DLA and LWFA, offering significant benefits for applications such as particle collimation, high-flux particle sources, and coherent radiation sources in new relativistic regimes.

In this study, we numerically simulate the evolution of the orbital angular momentum (OAM) spectrum of a vortex laser beam in the optical parametric chirped pulse amplification (OPCPA) process, which is an effective technical method to realize ultra-intense and ultra-short vortex laser amplification. The results show that the proportion of the vortex laser beam with 100% topological charge (TC) of 1 decreases to 97.44% with the enhancement of the saturation amplification after amplification by a 15 mm length LBO pumped by a 526.5 nm laser with a pump intensity of 1.74 GW/cm2. Conversely, the beams with other topological charges generate and increase with the amplification. The simulation results are consistent with our previous experimental results. Meanwhile, compared with non-collinear OPCPA, collinear OPCPA can maintain well the proportion of TC [Formula: see text].

In this letter, we report the demonstration of terawatt (TW)-scale femtosecond vortex laser pulses based on noncollinear optical parametric chirped-pulse amplification (OPCPA) centered at 800 nm.To the best of our knowledge, this is the first experimental study of amplification for OPCPA-based vortex pulses to achieve a powerful ultrafast (TWscale) vortex pulse output.In this experiment, a 0.5-mJ broadband chirped vortex pulse was amplified to 47 mJ with a 15-mm-long LiB 3 O 5 crystal.The double-pass grating pair compressor with an efficiency of 65% maintained the beam vortex, and a pulse of width 30.1 fs was obtained, corresponding to a peak power of 1.02 TW.This laser can be used in studies on nonlinear optics and relativistic laser-plasma interactions, compact plasmabased accelerators, and light sources.

We theoretically and experimentally demonstrate that high-purity Laguerre-Gaussian beams can be efficiently obtained from Gaussian vortex beams using a typical 4F spatial filtering optical system, in which spatial filtering does not affect the spiral phase and the energy loss is very small. In the Fourier frequency domain, aperture filtering specifically removes the high-frequency component corresponding to the central singularity region. In the spatial domain, aperture filtering corresponds to a convolution, which can smooth the central singularity region. This approach is simple and effective and has practical implementations in the generation and amplification of relativistic vortex beams.

A stable self-starting mode-locked Nd:YVO4 laser with a Herriott-type multiple-pass cavity (MPC) operating at 1 064 nm is demonstrated. An in-band 880-nm laser diode is used as an end-pump and a semiconductor saturable absorber mirror (SESAM) is used for passive mode locking (ML) and providing pulse durations of 14 ps. At a pump power of 26.4 W, the maximum average output power is as high as 10.5 W at a repetition rate of 22 MHz, which corresponds to a single pulse energy of 0.48 \mu J. Optical-tooptical conversion efficiency is as high as 39.8% at the maximum output power with a slope efficiency of 55.2%.