Highly stable, 54mJ Yb-InnoSlab laser platform at 0.5kW average power

Ultrafast 10 mJ, 100 W laser system featuring a directly laser written depolarization compensation element

In this study we demonstrated a compact and cost-effective high energy and average power picosecond laser developed for OPCPA system pumping applications. The system delivered record high pulse energy at 100 W average power level in a hybrid laser architecture based on a fiber seed laser and free-space end-pumped Yb:YAG amplifiers. The output pulses were compressed to 1 ps pulse duration and the output beam featured M2 = 1.3, which was further improved to 1.07 by spatial filtering. A silica glass spatially variable wave plate manufactured by direct laser writing was used to reduce depolarization losses from 12% to 5%.

417 W, 2.38 mJ Innoslab amplifier compressible to a high pulse quality of 406 fs

We demonstrate a 417 W, 175 kHz Innoslab chirped pulse amplification laser compressible to short and clean 406 fs pulse duration. A spectral bandwidth (full width at half maximum, FWHM) of ∼3 nm was maintained at full pump power, and the pulses exhibited good pulse quality in a wide tunable pulse energy range from 1.7 mJ to a maximum of 2.38 mJ. At the maximum output power, the compressed pulses were nearly pedestal free. The comprehensive effects of residual high-order dispersion from the front end, the gain shaping effects of the amplifier, and the slight mismatch of third-order dispersion (TOD) between the stretcher (CFBG) and the gating compressor, along with the small nonlinear phase shift accumulated in the amplifier, could have facilitated the high pulse quality. To the best of our knowledge, this is the shortest pulse duration from the Innoslab amplifiers at hundreds of watts average power in the millijoule energy regime.

Complete characterization of a Yb-based OPA at a high repetition rate using frequency resolved optical switching

We demonstrate experimentally that frequency resolved optical switching (FROSt) can be used to characterize ultra-broadband pulses at high repetition rates up to 500 kHz. Specifically, we present the complete temporal characterization of an optical parametric amplifier (OPA), from the supercontinuum (SC) to the second stage of amplification. Simultaneous characterization of co-propagating signal and idler pulses enables retrieval of their group delay, as well as their temporal phase and intensity. Our study focuses on an extensive frequency range spanning the infrared region (1.2 to 2.4 µm) and confirms the strength and convenience of FROSt as a single tool for characterizing a wide range of pulses at high repetition rates.

Parametric waveform synthesis: a scalable approach to generate sub-cycle optical transients

The availability of electromagnetic pulses with controllable field waveform and extremely short duration, even below a single optical cycle, is imperative to fully harness strong-field processes and to gain insight into ultrafast light-driven mechanisms occurring in the attosecond time-domain. The recently demonstrated parametric waveform synthesis (PWS) introduces an energy-, power- and spectrum-scalable method to generate non-sinusoidal sub-cycle optical waveforms by coherently combining different phase-stable pulses attained via optical parametric amplifiers. Significant technological developments have been made to overcome the stability issues related to PWS and to obtain an effective and reliable waveform control system. Here we present the main ingredients enabling PWS technology. The design choices concerning the optical, mechanical and electronic setups are justified by analytical/numerical modeling and benchmarked by experimental observations. In its present incarnation, PWS technology enables the generation of field-controllable mJ-level few-femtosecond pulses spanning the visible to infrared range.

High-power femtosecond regenerative amplifier based on Yb:CaYAlO4 dual-crystal configuration

A thermal lens insensitive regenerative amplifier (RA) with a dual Yb:CaYAlO₄ (Yb:CYA) crystal configuration for extending gain spectra is demonstrated for the first time, to the best of our knowledge. By orthogonalizing the orientation of two a-cut Yb:CYA crystals in one RA, the Q switched spectrum with a full width at half maximum of 15.4 nm is generated, which is 1.5 and 1.6 times of the Q switched spectral bandwidth with π- and σ-polarization, respectively. With chirped pulses injection, this RA can deliver laser pulses with an average power exceeding 10 W at the repetition rate of 20-800 kHz and pulse energy of 1.5 mJ at 1 kHz. This is the highest average power from the Yb:CYA RA to the best of our knowledge. Finally, compressed pulses of 163 fs with 92% overall efficiency are realized. Thanks to the heat insensitive cavity design and excellent thermodynamic properties of the Yb:CYA crystal, the output laser beam is close to the diffraction limit with an M² value of 1.07 × 1.07.

Yb:YAG diverging beam amplifier with 20 mJ pulse energy and 1.5 kHz repetition rate

We have developed a laser system with a combination of record-breaking parameters for rod ytterbium-doped yttrium aluminum garnet (Yb:YAG) lasers with pulse energy 20 mJ, average power 30 W, and beam quality М²< 1.35. This record was achieved thanks to the Yb:YAG diverging beam amplifier (DBA) geometry, which allows combining efficient amplification with high average power, good beam quality, and high-energy pulse extraction.

Efficiency Enhancing Technique for Rod Fiber Picosecond Amplifiers with Optimal Mode Field Matching

A high power and high quality picosecond laser is crucial in MEMS fabrication regarding micromachines. Optimal seed beam coupling is an important precondition to enhance laser efficiency. However, empirical coupling limits its development. In this paper, the physical parameters related to coupling are determined. The relationships among them are established under optical mode matching constraints to satisfy optimal seed beam coupling. According to a theoretical analysis, the focal length cut-off and the optimal coupling position of the coupling lens are acquired. A maximum transmittance of 87.2% is acquired with a 6 W input seed power in the validation experiment. In further power amplification experiments, a diffraction-limited beam quality is achieved, with M²_X = 1.111, M²_Y = 1.017, an optical efficiency of 60.5% and a slope efficiency of 66%, benefiting from the previous theoretical guidance.

Efficient high-power orthogonal dual-slab Yb:KGd(WO4)2 laser oscillator with a TEM00 mode

We demonstrated a TEM₀₀ mode orthogonal dual-slab Yb:KG(WO₄)₂(Yb:KGW) laser oscillator with high average power. Polarization anisotropy of thermal lenses was investigated and alleviating the astigmatism based on orthogonal dual-slab. In addition, the laser polarization was directly controlled by adjusting the net gain of the two crystals. The maximum output power was highly enhanced compared with single crystal due to effective thermal distribution. For an absorbed pump power of 52.4 W, this oscillator delivered an average power of 26.5 W, corresponding to an optical-to-optical conversion efficiency of 50.6%. Meanwhile, the ellipticity of the output laser was optimized to 0.940. Nearly diffraction-limited beam quality was measured to be M x2= 1.19 and M y2=1.18.

Designing multi-mode anti-resonant hollow-core fibers for industrial laser power delivery

We investigate the design of hollow-core fibers for the delivery of 10s of kilowatt average power from multi-mode laser sources. For such lasers, delivery through solid-core fibers is typically limited by nonlinear optical effects to 10s of meters of distance. Techniques are presented here for the design of multi-mode anti-resonant fibers that can efficiently couple and transmit light from these lasers. By numerical simulation we analyze the performance of two anti-resonant fibers targeting continuous-wave lasers with M² up to 13 and find they are capable of delivering MW-level power over several kilometers with low leakage loss, and at bend radii as small as 35 cm. Pulsed lasers are also investigated and numerical simulations indicate that optimized fibers could in principle deliver nanosecond pulses with greater than 100 mJ pulse energy over distances up to 1 km. This would be orders of magnitude higher power and longer distances than in typical machining applications using the best available solid core fibers.

Chip-scale high-peak-power semiconductor/solid-state vertically integrated laser

Compact lasers capable of producing kilowatt class peak power are highly desirable for applications in various fields, including laser remote sensing, laser micromachining, and biomedical photonics. In this paper, we propose a high-peak-power chip-scale semiconductor/solid-state vertically integrated laser in which two cavities are optically coupled at the solid-state laser gain medium. The first cavity is for the intra-pumping of ytterbium-doped yttrium aluminum garnet (Yb:YAG) with an electrically driven indium gallium arsenide (InGaAs) quantum well, and the second cavity consists of Yb:YAG and chromium-doped yttrium aluminum garnet (Cr:YAG) for passive Q-switching. The proposed laser produces pulses as short as 450 ps, and an estimated peak power of 57.0 kW with a laser chip dimension of 1 mm³. To the best of our knowledge, this is the first monolithic integration of semiconductor and solid-state laser gain mediums to realize a compact high-peak-power laser.

Here the authors demonstrate chip-scale high-peak-power lasers by vertical integration of semiconductor and solid state laser gain mediums to reach the same maturity level as existing semiconductor lasers, which are suitable for miniaturization and cost-effective mass production.

Few-cycle Yb laser source at 20 kHz using multidimensional solitary states in hollow-core fibers

We demonstrate ultrashort pulse compression from 300 fs down to 17 fs at a repetition rate of 20 kHz and 160-µJ output pulse energy (3.2 W of average power) using multidimensional solitary states (MDSS) in a 1-meter hollow-core fiber (HCF) filled with N₂O. Under static pressure, thermal limitations at this repetition rate annihilate the MDSS with suppression of spectral broadening. The results obtained in differential pressure configuration mitigate thermal effects and significantly increase the range of repetition rate over which MDSS can be used to compress sub-picosecond laser pulses.

Energy scaling of carrier-envelope-phase-stable sub-two-cycle pulses at 1.76 µm from hollow-core-fiber compression to 1.9 mJ

We present the energy scaling of a sub-two-cycle (10.4 fs) carrier-envelope-phase-stable light source centered at 1.76 µm to 1.9 mJ pulse energy. The light source is based on an optimized spectral-broadening scheme in a hollow-core fiber and a consecutive pulse compression with bulk material. This is, to our knowledge, the highest pulse energy reported to date from this type of sources. We demonstrate the application of this improved source to the generation of bright water-window soft-X-ray high harmonics. Combined with the short pulse duration, this source paves the way to the attosecond time-resolved water-window spectroscopy of complex molecules in aqueous solutions.

High-power Yb:CALGO regenerative amplifier and 30 fs output via multi-plate compression

The pulse energy and average power are two long-sought parameters of femtosecond lasers. In the fields of nonlinear-optics and strong-field physics, they respectively play the role to unlock the various nonlinear processes and provide enough photon fluxes. In this paper, a high-energy and high-power Yb:CALGO regenerative amplifier with 120 fs pulse width is reported. This high-performance regenerative amplifier can work with high stability in a large tuning range of repetition rates. Varying the repetition rate from 3 to 180 kHz, the maximum output power of 36 W and the pulse energy up to 4.3 mJ, corresponding to a peak power of more than 20 GW are demonstrated. The output beam is near diffraction limited with M²= 1.09 and 1.14 on the horizontal and vertical directions, respectively. In addition, multi-plate compression is employed to achieve 30 fs output with 23 W average power which is attractive for applications such as high-harmonic generation.

Temporal pulse quality of a Yb:YAG burst-mode laser post-compressed in a multi-pass cell

Nonlinear pulse post-compression represents an efficient method for ultrashort, high-quality laser pulse production. The temporal pulse quality is, however, limited by amplitude and phase modulations intrinsic to post-compression. We here characterize in frequency and time domain with high dynamic range individual post-compressed pulses within laser bursts comprising 100-kHz-rate pulse trains. We spectrally broaden 730 fs, 3.2 mJ pulses from a Yb:YAG laser in a gas-filled multi-pass cell and post-compress them to 56 fs. The pulses exhibit a nearly constant energy content of 78% in the main peak over the burst plateau, which is close to the theoretical limit. Our results demonstrate attractive pulse characteristics, making multi-pass post-compressed lasers very applicable for pump-probe spectroscopy at, e.g., free-electron lasers or as efficient drivers for secondary frequency conversion stages.

1 kHz, 430 mJ, sub-nanosecond MOPA laser system

We demonstrate a sub-nanosecond MOPA system with a pulse repetition frequency of 1 kHz at 1.06 µm, based on an integrated seed source with pulse energy of 6.2 mJ and two conductively cooled end-pumped Nd:YAG slab gain modules. After a 4-pass amplification stage and a double-pass amplification stage with amplification factors of 12.6 dB and 5.84 dB, respectively, maximum pulse energy of 434 mJ with pulse duration of 691 ps was obtained, corresponding to a peak power of 628 MW. Via adjusting the pump distribution to compensate the static wavefront distortion of the signal laser, the beam quality, at the maximum pulse energy, was optimized to be 2.5 mm·mrad and 2.2 mm·mrad respectively in the vertical and transverse directions. The results benefit a variety of applications including material processing, nonlinear frequency conversion, and lidars.

Investigation of spatiotemporal output beam profile instabilities from differentially pumped capillaries

Differentially pumped capillaries, i.e., capillaries operated in a pressure gradient environment, are widely used for nonlinear pulse compression. In this work, we show that strong pressure gradients and high gas throughputs can cause spatiotemporal instabilities of the output beam profile. The instabilities occur with a sudden onset as the flow evolves from laminar to turbulent. Based on the experimental and numerical results, we derive guidelines to predict the onset of those instabilities and discuss possible applications in the context of nonlinear flow dynamics.

70 mJ nonlinear compression and scaling route for an Yb amplifier using large-core hollow fibers

In this Letter, we investigate the energy-scaling rules of hollow-core fiber (HCF)-based nonlinear pulse propagation and compression merged with high-energy Yb-laser technology, in a regime where the effects such as plasma disturbance, optical damages, and setup size become important limiting parameters. As a demonstration, 70 mJ 230 fs pulses from a high-energy Yb laser amplifier were compressed down to 40 mJ 25 fs by using a 2.8-m-long stretched HCF with a core diameter of 1 mm, resulting in a record peak power of 1.3 TW. This work presents a critical advance of a high-energy pulse (hundreds of mJ level) nonlinear interactions platform based on high energy sub-ps Yb technology with considerable applications, including driving intense THz, X-ray pulses, Wakefield acceleration, parametric wave mixing and ultraviolet generation, and tunable long-wavelength generation via enhanced Raman scattering.

60 fs, 1030 nm FEL pump-probe laser based on a multi-pass post-compressed Yb:YAG source

This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas-filled multi-pass cell to generate sub-100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 µJ, respectively, for pump-probe experiments at the free-electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump-probe experiments.

1.1 J Yb:YAG picosecond laser at 1 kHz repetition rate

We demonstrate the generation of 1.1 J pulses of picosecond duration at 1 kHz repetition rate (1.1 kW average power) from a diode-pumped chirped pulse amplification Yb:YAG laser. The laser employs cryogenically cooled amplifiers to generate λ=1030nm pulses with average power of up to 1.26 kW prior to compression with excellent beam quality. Pulses are compressed to 4.5 ps duration with 90% efficiency. This compact picosecond laser will enable a variety of applications that require high energy ultrashort pulses at kilohertz repetition rates.

Development of a 67.8 W, 2.5 ps ultrafast chirped-pulse amplification system based on single-crystal fiber amplifiers

We demonstrate a high-power, high-energy chirped-pulse amplification (CPA) system based on three Yb:YAG amplifiers and a chirped-volume Bragg grating (CVBG). With an all-fiber laser as the seed light, a Yb:YAG rod amplifier and two Yb:YAG single-crystal fiber (SCF) amplifiers as the amplification stages, a laser power of 96 W at 200 kHz repetition rate corresponding to a pulse energy of 0.48 mJ has been generated. The stability of different output power has been measured and compared. To the best of our knowledge, this is the first report on a stable 100 W-level laser with sub-mJ pulse energy based on SCF. The beam quality M² of different output lasers has also been measured, which is below 1.55 when the output power is 92 W. The amplified laser is seeded into the CVBG to be compressed, and a compression efficiency of 0.724 has been obtained with an output power of 67.8 W and pulse duration of 2.5 ps. The ultrafast CPA system delivering high pulse energy (sub-mJ) with hundreds of kHz repetition rate is expected to be used as the driving source of high-flux high-harmonic generation after further compression.

High energy redshifted and enhanced spectral broadening by molecular alignment

We demonstrate an efficient approach for enhancing the spectral broadening of long laser pulses and for efficient frequency redshifting by exploiting the intrinsic temporal properties of molecular alignment inside a gas-filled hollow-core fiber (HCF). We find that laser-induced alignment with durations comparable to the characteristic rotational time scale TRotAlign enhances the efficiency of redshifted spectral broadening compared to noble gases. The applicability of this approach to Yb lasers with (few hundred femtoseconds) long pulse duration is illustrated, for which efficient broadening based on conventional Kerr nonlinearity is challenging to achieve. Furthermore, this approach proposes a practical solution for high energy broadband long-wavelength light sources, and it is attractive for many strong field applications.

Postcompression of picosecond pulses into the few-cycle regime

In this work, we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.

High-field mid-infrared pulses derived from frequency domain optical parametric amplification

We present a novel, to the best of our knowledge, approach for scaling the peak power of mid-infrared laser pulses with few-cycle duration and carrier-to-envelope phase stabilization. Using frequency domain optical parametric amplification (FOPA), selective amplification is performed on two spectral slices of broadband pulses centered at 1.8 µm wavelength. In addition to amplification, the Fourier plane is used for specific pulse shaping to control both the relative polarization and the phase/delay between the two spectral slices of the input pulses. At the output of the FOPA, intrapulse difference frequency generation provides carrier-envelope phase stabilized two-cycle pulses centered at 9.5 µm wavelength with 25.5 µJ pulse energy. The control of the carrier-envelope phase is demonstrated through the dependence of high-harmonic generation in solids. This architecture is perfectly adapted to be scaled in the future to high average and high peak powers using picosecond ytterbium laser technologies.

Laser with 1.2 ps, 20 mJ pulses at 100 Hz based on CPA with a low doping level Yb:YAG rods for seeding and pumping of OPCPA

We report on a picosecond two-stage double-pass chirped pulse amplifier based on a low doping level Yb:YAG rods. After compression, it provides output pulses with a pulsewidth of 1.15 ps and an energy of more than 20 mJ at a repetition rate of 100 Hz with a beam quality of M2 ∼1.05. These pulses were frequency doubled in a two-cascaded second harmonic converter based on LBO and BBO crystals with an output energy of 12 mJ and 5 mJ at 515 nm, suitable for simultaneously pumping OPCPA cascades.

Scalable 30 fs laser source with 530 W average power

We present a power-scalable laser source with 30 fs pulse duration, 530 W average power at 500 kHz repetition rate, and beam quality M²<1.2. The compact and efficient setup consists of ytterbium-based Innoslab amplifiers and subsequent nonlinear pulse compression with an argon-filled Herriott cell.

Picosecond slab regenerative amplifier using a large fundamental mode stable-unstable hybrid cavity

Slab gain media with large aspect ratios were difficult to be adopted in ultrafast regenerative amplifiers (RAs) due to the obstacle of mode matching with the seed beam. We proposed that an unstable cavity could be employed to solve this difficulty by taking the advantage of its large fundamental mode volume. In this way, an Nd:YVO₄ slab-based picosecond RA has been successfully demonstrated using a stable-unstable hybrid cavity. The maximum average output power of 10.5 W was achieved at the repetition rate of 10 kHz. The beam quality factor M² was measured to be 1.54 in the stable direction and 2.26 in the unstable direction.

Peak power & average power scaling via fourier domain OPA (FOPA)

FoTaking advantage of pulse shortening upon amplification, we demonstrate 2.5TW pulses (30mJ, 2 cycle, 1.8 μm) based on TiSa pumping, while for boosting average power we utilize a 500W Yb platform for pump and seed pulses.

Thin-rod Yb:YAG amplifiers for high average and peak power lasers

The concept of a high-power thin-rod Yb:YAG laser amplifier with high-brightness diode pumping was proposed. The principle of the amplifier parameter variation aimed at achieving an efficient signal gain at different power levels was developed. Three versions of thin-rod gain modules were implemented, where small and strong signal gains were studied experimentally. The ultrafast laser system with high average power (28 W) and high pulse energy (2.5 mJ) was created on the basis of the unique thin-rod gain modules.

Direct compression of 170-fs 50-cycle pulses down to 1.5 cycles with 70% transmission

We present a straightforward route for extreme pulse compression, which relies on moderately driving self-phase modulation (SPM) over an extended propagation distance. This avoids that other detrimental nonlinear mechanisms take over and deteriorate the SPM process. The long propagation is obtained by means of a hollow-core fiber (HCF), up to 6 m in length. This concept is potentially scalable to TW pulse peak powers at kW average power level. As a proof of concept, we demonstrate 33-fold pulse compression of a 1 mJ, 6 kHz, 170 fs Yb laser down to 5.1 fs (1.5 cycles at 1030 nm), by employing a single HCF and subsequent chirped mirrors with an overall transmission of 70%.

10 W CEP-stable few-cycle source at 2 µm with 100 kHz repetition rate

We developed a high repetition rate optical parametric chirped-pulse amplification (OPCPA) laser system based on fiber-laser-seeded Innoslab to generate few-cycle pulses around 2 µm with passively stable carrier-envelope phase (CEP) by difference frequency generation (DFG). Incorporating a piezo mirror before the DFG stage permits rapid CEP control. The OPCPA system is seeded by a stable supercontinuum generated in bulk material with the picosecond Innoslab pulses. Few-cycle pulses with durations of 17 fs and energies of over 100 μJ were produced in a single OPCPA stage. Three different nonlinear crystals: BBO, BiBO, and LNB were tested in the final parametric amplifier, and their average power related limitations are addressed.