Showing papers on "Regenerative amplification published in 2021"

Compact OPCPA system seeded by a Cr:ZnS laser for generating tunable femtosecond pulses in the MWIR

Abstract: A compact mid-wavelength infrared (MWIR) optical parametric chirped pulse amplification (OPCPA) system generates sub-150 fs pulses at wavelengths from 5.4 to 6.8 µm with >400µJ energy at a 1 kHz repetition rate. A femtosecond Cr:ZnS master oscillator emitting 40 fs pulses at 2.4 µm seeds both a Ho:YLF regenerative amplifier and a two-stage OPCPA based on ZnGeP2 crystals. The 2.05 µm few-picosecond pump pulses from the Ho:YLF amplifier have an energy of 13.4 mJ. Seed pulses for the OPCPA are generated by soliton self-frequency shifting in a fluoride fiber and are tunable between 2.8 and 3.25 µm with a sub-100 fs duration and few-nanojoule energy. The intense MWIR pulses hold strong potential for applications in ultrafast mid-infrared nonlinear optics and spectroscopy.

Multigigawatt 50 fs Yb:CALGO regenerative amplifier system with 11 W average power and mid-infrared generation

Abstract: Lasers with high average and high peak power as well as ultrashort pulse width have been all along demanded by nonlinear optics studies, strong-field experiments, electron dynamics investigations, and ultrafast spectroscopy. While the routinely used titanium-doped sapphire (Ti:sapphire) laser faces a bottleneck in the average power upscaling, ytterbium (Yb)-doped lasers have remarkable advantages in achieving high average power. However, there is still a substantial gap of pulse width and peak power between the Ti:sapphire and Yb-doped lasers. Here we demonstrate a high-power Yb:CaAlGdO4 (Yb:CALGO) regenerative amplifier system, delivering 1040 nm pulses with 11 W average power, 50 fs pulse width, and 3.7 GW peak power at a repetition rate of 43 kHz, which to some extent bridges the gap between the Ti:sapphire and Yb lasers. An ultrabroadband Yb-doped fiber oscillator, specially designed spectral shapers, and Yb:CALGO gain medium with broad emission bandwidth, together with a double-end pumping scheme enable an amplified bandwidth of 19 nm and 95 fs output pulse width. To the best of our knowledge, this is the first demonstration of sub-100 fs regenerative amplifier based on Yb-doped bulk medium without nonlinear spectral broadening. The amplified pulse is further compressed to 50 fs via cascaded-quadratic compression with a simple setup, producing 3.7 GW peak power, which boosts the record of peak power from Yb:CALGO regenerative amplifiers by 1 order. As a proof of concept, pumped by the high-power, 50 fs pulses, 7.5–11.5 µm mid-infrared (MIR) generation via intrapulse difference-frequency generation is performed, without the necessity of nonlinear fiber compressors. It leads to a simple and robust apparatus, and it would find good usefulness in MIR spectroscopic applications.

Highly efficient cryogenic Yb:YLF regenerative amplifier with 250 W average power.

Abstract: We report an efficient diode-pumped high-power cryogenic regenerative amplifier operating at 1019 nm employing the c axis of Yb:YLF. Compared to the usually selected 1017 nm transition of the a axis, the c-axis 1019 nm line has a three-fold higher emission cross section and still possesses a full-width at half-maximum (FWHM) of 6.5 nm at 125 K. The chirped-pulse amplifier system is seeded by a fiber front-end with energy of 30 nJ and a stretched pulse width of 2 ns. In regenerative amplification studies, using the advantage of higher gain in the c axis, we have achieved record average powers up to 370 W with an extraction efficiency of 78% at a 50 kHz repetition rate. The output pulses were centered on 1019.15 nm with a FWHM bandwidth of 1.25 nm, which supports sub-1.5 ps pulse durations. The output beam maintained a TEM00 beam profile at output power levels below 250 W with an M2 below 1.2. Above this power level, the thermally induced lensing in Yb:YLF created a multimode output beam. The thermal lens was rather dynamic and deteriorated the system stability above a 250 W average power level.

Reducing temporal pedestal in a Ti:sapphire chirped-pulse amplification system by using a stretcher based on two concave mirrors.

Abstract: We demonstrate the temporal pedestal suppression in a Ti:sapphire chirped-pulse amplification laser system. The far-field spectral phase noise can be avoided by using a stretcher based on two concave mirrors in the system, reducing the intensity and the time range of the amplified pulse’s pedestal. At the amplified energy of 1.7 J, the contrast measurement showed that the pedestal intensity was at a level of about 10−10 within a 10 ps time window near the main pulse. In the proton acceleration experiment, a 10 nm thickness CH target was irradiated by the high-contrast pulse with the focused intensity of ∼1.4×1020W/cm2, which generated a proton beam with a cutoff energy of 16 MeV.

Comparative investigation of lasing and amplification performance in cryogenic Yb:YLF systems

Abstract: We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We have comparatively investigated continuous-wave (cw) lasing and regenerative amplification performance under different experimental conditions. In the cw lasing experiments effect of crystal doping, cw laser cavity geometry and pump wavelength on lasing performance were explored. Regenerative amplification behavior was analyzed and the role of depolarization losses on performance was investigated. A recently developed temperature estimation method was also employed for the first time in estimating average crystal temperature under lasing conditions. It is shown that the thermal lens induced by transverse temperature gradients is the main limiting factor and strategies for future improvements are discussed. To the best of our knowledge, the achieved results in this study (375 W in cw, and 90 W in regenerative amplification) are the highest average powers ever obtained from this system via employing the broadband E//a axis.

Generation of wavelength-tunable few-cycle pulses in the mid-infrared at repetition rates up to 10 kHz.

Abstract: We demonstrate a compact and tunable mid-infrared light source that provides carrier-envelope-phase (CEP)-locked pulses at repetition rates from 500 Hz to 10 kHz. The seed pulses were generated by intra-pulse difference frequency mixing of the output of an Yb:KGW regenerative amplifier that had been spectrally broadened by continuum generation using multiple plates. Then, a two-stage optical parametric amplifier was used to obtain output energies of about 100 µJ/pulse for center wavelengths between 2.8 and 3.5 µm. Owing to the intense pulse energies, it was possible to compress the multi-cycle pulses down to two-cycle pulses using YAG and Si plates.

120 mJ, 1 kHz, picosecond laser at 515 nm.

Abstract: We report on a 1 kHz, 515 nm laser system, based on a commercially available 230 W average power Yb:YAG thin-disk regenerative amplifier, developed for pumping one of the last optical parametric chirped pulse amplification (OPCPA) stages of the Allegra laser system at ELI Beamlines. To avoid problems with self-focusing of picosecond pulses, the 1030 nm output pulses are compressed and frequency doubled with an LBO crystal in vacuum. Additionally, development of a thermal management system was needed to ensure stable phase matching conditions at high average power. The resulting 515 nm pulses have an energy of more than 120 mJ with SHG efficiency of 60% and an average RMS stability of 1.1% for more than 8 h.

LED-pumped femtosecond Cr:LiSAF regenerative amplifier system.

Abstract: We report on the first, to the best of our knowledge, LED-pumped femtosecond regenerative amplifier. It is based on a Cr:LiSAF crystal pumped by 2240 blue LEDs via a Ce:YAG luminescent concentrator. The amplifier was seeded by pulses from a Ti:sapphire oscillator at 835 nm temporally stretched from 90 fs to 100 ps. At the output of the regenerative amplifier, we obtain 1 mJ pulse energy at a 10 Hz repetition rate, given by the frequency of the LED-pumping module. After compression, we obtain 100 fs pulses with a spectral bandwidth of 10 nm at 835 nm.

High power (>500W) cryogenically cooled Yb:YLF cw-oscillator operating at 995 nm and 1019 nm using E//c axis for lasing.

Abstract: We present record continuous wave (cw) output power levels from cryogenically cooled Yb:YLiF4 (Yb:YLF) lasers in rod geometry. The laser system is pumped by a state-of-the-art 960 nm diode module, and vertically polarized lasing was employed using the E//c axis of Yb:YLF. Lasing performance was investigated at different output coupling levels in different cavity configurations and the laser crystal temperature was estimated via monitoring the emission spectrum of the gain media. We have obtained a cw output power up to 400 W at a wavelength of 995 nm. The absorbed pump power was around 720 W, and the laser output had a TEM00 beam profile with an M2 of 1.3 in both axes. At higher absorbed pump power levels with increasing laser crystal temperature, we observed a lasing wavelength shift from 995 nm to 1019 nm. In this regime cw output power levels above 500 W have been achieved at an absorbed pump power of 750 W. Further power scaling was limited by the onset of strong thermal lensing. We discuss underlying physical mechanisms for the wavelength shift and present detailed temperature measurements under lasing conditions.

Guiding of Laser Pulses at the Theoretical Limit – 97% Throughput Hollow-Core Fibers

Abstract: The results are based on a commercial Yb:KGW regenerative amplifier (Pharos, Light Conversion) delivering 1 mJ, 170 fs pulses at 1 to 6 kHz. This beam is precisely matched to the fundamental mode of a large core HCF ( few-cycle Inc.) of 1 mm inner diameter, by realizing a focal spot diameter of 660 μm at 1/e 2 of intensity (corresponding approximately to a Rayleigh range of 0.3 m).

High-stability, high-energy Nd:glass rod regenerative amplifier with compensation for cavity misalignment.

Abstract: We report on an Nd:glass large-mode rod regenerative amplifier with a pulse energy of 125 mJ at 1053 nm. The amplifier contains a linear-type resonator, which is designed in Stability Zone II with a misalignment sensitivity factor of 12.9 m. A method is proposed for analyzing the sensitivity of the mode displacement on the gain media to cavity misalignment, and the optimum solution to compensation for cavity misalignment is obtained and applied to the amplifier. The amplifier exhibits excellent energy stability with a fluctuation of 0.47% (RMS) within 7 h and high spatial beam quality with M2=1.17. The beam pointing stability in the horizontal and vertical axes within 7 h is 2.7 and 3.6 µrad (RMS), respectively.

20-W, 168 fs Yb:CALGO regenerative amplifier with 1-MHz repetition rate

Abstract: We report on a 1-MHz repetition rate regenerative amplifier based on single Yb:CALGO crystal. It delivers 168 fs pulses with 20 W average power, centered at 1040 nm with a spectral bandwidth of 11 nm.

Thin-disk multipass amplifier for kilowatt-class ultrafast lasers above 100 mJ

Abstract: We present a linear multipass amplifier based on the thin-disk technology which allows power scaling of continuous-wave, pulsed, and ultrashort-pulsed lasers without change of beam characteristics. The flexibility of the seed laser, such as choice of repetition rate, pulse duration, and bursts is maintained. Due to a large beam radius on the thin disk of several millimeters, peak intensities are lower and nonlinear effects play a smaller role compared to the competing technologies of fiber and slab amplifiers. The multipass amplifier consists of a glass-welded mirror array and a thin-disk laser head. An Ytterbium-doped thin disk with a thickness on the order of few 100 μm acts as the active medium. The mirror array is used to implement up to 36 reflections at the disk.

100 fs LED-pumped Cr:LiSAF regenerative amplifier

Abstract: Transition metal-doped gain media such as Ti:sapphire, Cr:LiSAF and Alexandrite are the most appropriated crystals for femtosecond laser chains with pulse duration below 100 fs. However, because of a low gain and an absorption band in the green/red region, these materials are difficult to pump directly with diodes. Hence, the main issue for a femtosecond laser chain is the complexity and the high cost of the pump sources for the amplifiers. One innovative solution is to take advantage of the compactness, robustness, and low price of the light-emitting diodes (LED) to pump transition metal-doped gain media. In this work, we report, to our best knowledge, the first femtosecond amplifier pumped by LED. For this demonstration, we choose the Cr:LiSAF crystal for its combination of high absorption, large emission cross section and relatively long radiative lifetime. We then present a LED-pumped Cr:LiSAF regenerative amplifier in a femtosecond laser chain.

160W Cryogenic Regenerative Yb:YLF Amplifier

Abstract: Nowadays the compact high power and high energy laser sources could be used for a variety of scientific and industrial applications as high harmonic generation, electron acceleration and material processing [1] . Although the room-temperature laser systems can provide millijoule energy at high average powers of hundreds of watts with pulse widths in the 0.5-5 ps, yet that requires to a complicated laser architecture [2] , [3] . The lasers operating at cryogenic temperatures exhibit simpler optical design together with a pristine beam quality [4] . In this work we propose as an attractive crystal choice of Yb:YLF (Yb:LiYF 4 ) for cryogenic regenerative amplifiers. Yb:YLF crystal combine adequate thermomechanical strength with a relatively broad gain bandwidth that could ideally support amplification of sub-250-fs pulses [4] .

Robust Self-Referenced Generator of Programmable Multi-Millijoule THz-Rate Bursts

Abstract: The generation of ultrashort laser pulse bursts has already contributed to many applications such as materials processing [1] , pulsed laser deposition [2] , laser induced breakdown spectroscopy (LIBS) [3] and seeding of free electron lasers [4] . Currently, there is a rising demand on burst sources providing terahertz (THz) intraburst repetition rates or higher corresponding to pulse spacings in the order of a few picoseconds, given by applications such as resonant driving of optical nonlinearities [5] , time-resolved nonlinear spectroscopies [6] , coherent control of quantum systems [7] or as driver for secondary radiation sources, e.g. generation of THz bursts [8] . However, the amplification of bursts to multi-millijoule energies at THz intraburst repetition rates is highly problematic. This is given by the appearance of spectral modes that are mapped into the time-domain, formed by spectral interference of closely spaced pulses which are overlapping when applying Chirped Pulse Amplification (CPA). This leads to insufficient energy extraction in an amplifier and, if pulse spacing is not stabilized on an interferometric scale, to temporally unstable burst generation. Recently, we have successfully demonstrated energy-safe, stabilized CPA of ultrashort pulse bursts with THz intraburst frequencies up to multi-millijoules by applying Vernier-enabled phase-modulation techniques, breaking the mentioned energy-limiting barrier [8] . In this contribution, we demonstrate a new version of our burst-generation technique, which drastically lowers system complexity compared to our previous approach, allowing its application to any master-oscillator regenerative-amplifier combination setup with only minor modifications.

High repetition-rate 1,2 Terawatt diode pumped laser

Abstract: We report a diode-pumped laser delivering 518mJ and 435fs pulse duration at 50Hz repetition rate, corresponding to 1,2 Terawatt peak power. The pulse is 3% close to TF limit, and the Strehl ratio is 0,91.

Design and real-time control of the OPD from 20 to 200°C in a cat's-eye cavity using thick slabs of Yb 3+ : YAG for athermal amplification

Abstract: We demonstrate an athermal, 100 mJ-energy class Yb3+: YAG slab-based amplifier designed to operate in the range of temperatures from 20 to 200°C. The gain medium consists of an edge-pumped, thick slab with a folded laser beam-path, which is defined in a cat's eye cavity thanks to 6–12 elementary paths. Highly variable operating conditions are investigated, in a close connection with the induction of severe thermal penalties in the slab. These penalties concern the material's spectroscopic properties and the thermo-mechanical distortions, at the location of the laser faces. Looking at the shape of the optical-path-difference (OPD) along the slab, we evidence a strong dependency with the pump-dependent temperature cartography inside. This involves comprehensive fits between the measurement data and Finite Element Modeling (FEM) results. As a follow-up, by closely coupling a movable cylindrical lens along the slab, we validate the efficiency of an easy-to-implement correction process to cancel the OPD in the real time. Regardless of the operating regime, this enables fully updatable lasing conditions with reduced output beam distortions in the far field of the cavity output.

Highly stable sub-nanosecond Nd:YAG pump laser for optically synchronized optical parametric chirped-pulse amplification.

Abstract: We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only <0.2% (rms). With an external LBO doubler, the system generated 330 ps green pulse energy of 130 mJ at 532 nm with a conversion efficiency of 65%. The pulse duration was further extended to 490 ps by adjusting Nd:YAG crystal temperature. To the best of our knowledge, these results present a longer pulse duration with higher stability than previous Nd:YAG lasers with sub-nanosecond optical synchronization.

OPCPA Front-End based on a Cr:ZnS Laser for Femtosecond Pulse Generation in the Mid-Infrared

Abstract: Mid-infrared (mid-IR) OPCPA architectures rely on rather complex front-ends where the seeds for pump and signal pulses are provided by a combination of nonlinear effects such as supercontinuum and difference frequency generation or OPG/OPA [1] , [2] . The involved cascaded nonlinear stages increase the complexity and reduce the stability and efficiency of the OPCPA. Here we present an alternative based on a fs Cr:ZnS master oscillator whose emission spectra include pump and signal [3] , which significantly simplifies mid-IR OPCPA. Furthermore, its implementation in a mid-IR OPCPA is demonstrated.

High Average Power and High Energy Yb:YLF Cryogenic Amplifiers

Abstract: We present initial results from a high-power and high energy sub-ps cryogenic Yb:YLF amplifier chain centered around 1018.5 nm. We have so far achieved average powers above 90-W and pulse energies up to 305 mJ.

Ultrashort green laser pulse amplification in praseodymium doped LiYF 4 crystal pumped by InGaN based laser diodes

Abstract: A green laser pulse (peak wavelength of 522.4 nm) was amplified as 12.5 times from 0.1 to 1.25 µJ in a regenerative amplifier using a Pr3+:LiYF 4 crystal pumped by InGaN based laser diodes.

Reaching the Millijoule-Regime via Ultrafast Optical Parametric Amplification – An Alternative to First Stage Regenerative Amplification Stages?

Abstract: A new ultra-high contrast uOPA module is being developed for the PHELIX- and PENELOPE frontend-chains. This module will enhance the ASE-contrast and prevent the formation of pre-pulses through a bypass of high-gain amplifiers.