Regenerative Amplifier Research Articles

Green pulse regenerative amplification using a Pr3+:LiYF4 crystal pumped by GaN blue laser diodes

Green pulse regenerative amplification using a Pr3+:LiYF4 crystal pumped by GaN blue laser diodes

High-efficiency Yb:YAG thin-disk chirped pulse amplifier delivering 884-femtosecond laser with tunable repetition rates and high stability

We experimentally demonstrated a compact, highly efficient, stable, chirped pulse amplification (CPA) thin-disk regenerative system with a tunable repetition rate. The laser head consists of a 9 at. % Yb:YAG thin-disk with a diameter of 8.8 mm and a thickness of 150 μm, is designed for a 48-pump pass configuration. In CPA-based regenerative amplifier configuration, a maximal output power of 85 W at 500 kHz is achieved with a conversion efficiency of 53.1 %. This corresponds to a pulse energy of 170 μJ. To the best of our knowledge, this is the highest conversion efficiency in CPA thin-disk regenerative amplifiers. The pulse width is compressed to 884 fs with a pair of grating, resulting in a peak power of 192 MW. At 85 W, a near diffraction limit beam quality factor M2 of 1.40 is measured, which is essential in precision applications. In addition, remarkable long-term power stability is confirmed with a root-mean-square (RMS) fluctuation of 0.12 % over a 24-hour duration. The reported femtosecond amplifier is believed to be a promising tool for various applications such as extreme manufacturing, terahertz spectroscopy, etc.

1 kHz, 10 mJ, sub-200 fs regenerative amplifier utilizing a dual-crystal configuration of Yb:CaGdAlO4 featuring exceptional beam quality

In order to boost the energy of the femtosecond regenerative amplifier (RA), we adopt the chirped pulse amplification technique to stretch the seed pulses through the Martinez stretcher and inject them into our specially designed dual-crystal regenerative cavity based on the Yb:CaGdAlO4 (Yb:CGA) crystals. To avoid damaging the component coating, we meticulously regulate the size of the cavity mode on the surface of each component within the cavity to ensure that the energy density remains below the damage threshold. The final output of 11.3 mJ pulse energy was obtained at a 1 kHz repetition rate with a power stability of 0.35% over 1 hour, which is the highest energy we know of for the regenerative output of Yb:CGA crystals. Additionally, leveraging the wide gain spectrum of the Yb:CGA crystal, we achieve a spectrum full width at half maximum (FWHM) of 9 nm along with a compressed pulse duration of 198 fs. The combination of the dual-crystal setup, superior thermal properties of the Yb:CGA crystals, quasi-continuous wave pumping approach, and the thermal-insensitive design of the regenerative cavity effectively minimize the thermal impact on the crystals. The output beam exhibits near-diffraction-limited performance, with an M2 value of only 1.05 × 1.06.

High-gain Ho:YLF sub-nanosecond system seeded by a gain-switched laser diode

We demonstrate a high-gain Ho:YLF sub-nanosecond laser system utilizing a gain-switched laser diode as the seed source. The 1.0 kHz pJ-level seed from the gain-switched laser diode is first amplified to 1.1 mJ by a Ho-doped fiber preamplifier with a gain of 30 dB and a regenerative amplifier (RA) with a gain of 60 dB. By adding a single-pass amplifier, the pulse energy is further extended to 7.5 mJ. A pulse duration of 518.5 ps was achieved, which is symmetrical with no tail or sub-peaks. The root mean square (RMS) stability of the output energy of the entire system over a 0.5 h period is 2.11%. This method provides a reliable and simple way to directly obtain high-energy 2.05 µm sub-nanosecond lasers.

2.09 µm high-gain, high-energy sub-nanosecond laser amplification system and its application to a millijoule-level mid-infrared ZnGeP2 optical parametric generator.

In this Letter, we report for the first time to our knowledge a 2 mJ-level 2.09 µm Ho:YAG regenerative amplifier (RA) seeded by the first-stage Ho-doped fiber (HDF) preamplifier of a gain-switched laser diode (GSLD). After the single-pass power amplifier (SPPA), the output of a 2.09 µm pulse laser with 1 kHz, 570 ps, and >10 mJ was achieved. The overall gain of the whole amplifier system was greater than 90 dB, providing a novel, stable, and reliable sub-nanosecond (sub-ns) pump source operating at a pulse repetition frequency (PRF) of 1 kHz for an optical parametric generator (OPG) based on ZnGeP2 (ZGP). Specifically, for the ZGP OPG structure, a maximum pulse energy of 1.82 mJ at 3-5 µm had been achieved with an injected pump pulse energy of 5.47 mJ, corresponding to a slope efficiency of 39.5% and an optical-to-optical conversion efficiency (OOCE) of 33.27%.

In vivo biological safety investigation of Yb-CALGO femtosecond laser dental surgery.

While lasers have found their successful applications in various clinical specialties, in clinical dental practice, traditional mechanical drills are still predominantly utilized. Although erbium-doped lasers have been demonstrated for dental therapy, their clinical performance is still not satisfactory due to the long pulse width, low peak power, and small repetition rate. To attain a smaller thermal diffusion thus better biological safety and surgical precision, as well as more rapid ablation, the advancement of femtosecond laser techniques has opened another route of dental surgery; however, no biological safety investigation has been reported. Here, we present a systematic study of dental ablation by a Yb:CaAlGdO4 regenerative amplifier with a central wavelength of 1040 nm and pulse width of 160 fs. The in vivo experiment of dental surgery investigating the inflammatory response has been reported, for the first time to the best of our knowledge. It is demonstrated that dental surgery by Yb:CaAlGdO4 femtosecond laser ablation has better biological safety compared to the turbine drilling, thanks to its non-contact and ultrafast heat dissipation nature.

Ho:YLF regenerative amplifier delivering 22 mJ, 2.0 ps pulses at a 1 kHz repetition rate

We report on a high-energy, few-ps, continuous-wave pumped Ho:YLF regenerative amplifier (RA) operating in a chirped-pulse amplification arrangement. A three-stage optical parametric amplifier serves as versatile seed source emitting broadband pulses centered at 2050 nm. It provides seed pulses with 4 µJ energy within the Ho:YLF amplification bandwidth centered at 2051 nm. Thanks to the high seed pulse energy, bifurcation instabilities are mitigated and gain narrowing is reduced for such a high-gain Ho-doped RA operating at few kHz repetition rate. At 1 kHz the Ho:YLF RA emits 22.5 mJ energy pulses with a compressed pulse duration of 2.0 ps in the stable single-pulse regime. The water cooled RA features a high extraction efficiency of 31% and exhibits a remarkable stability of 0.11% rms. Doubling the repetition rate to 2 kHz, RA pulse energy reaches 15 mJ. The demonstrated 10 GW peak power at 1 kHz and the 30 W average power at 2 kHz are the highest values reported to date for few-ps RAs operating at 2 µm wavelength.

Cpa-free Yb:YAG thin-disk regenerative amplifier laser with hundreds of watts, hundreds of kHz, and hundreds of picoseconds

This paper introduces a CPA-free Yb:YAG thin-disk regenerative amplifier laser system. The seed pulse is generated by a passive mode-locked picosecond oscillator based on a semiconductor saturable absorber mirror, with a center wavelength of 1030.7 nm, a pulse width of 7.7 ps, and a repetition frequency of 26.3 MHz. After stretched and pre-amplified by an all-fiber front stage, the seed with a pulse width of 201.3 ps and a pulse energy of 15.2 nJ was obtained, then injected into the thin-disk regenerative amplifier. Yb:YAG crystal was chosen as the material for the thin-disk, with 100 μm thickness, 9 mm diameter and 7 at.% doping rate. In order to increase the one-way round-trip gain of the thin-disk regenerative amplifier, a symmetrical dual-pass resonant cavity was designed to double the number of passing through the crystal on a round trip in the regenerative resonant cavity to reduce the times of cycles, intra-cavity loss and improve optical efficiency. We used a 969 nm fiber-coupled semiconductor laser as the pump source to pump the Yb:YAG thin-disk crystal. With zero-phonon line pumping technology, the quantum loss and thermal effect were reduced. In the end, we obtained a regenerative amplification output with an average power of 104.5 W, a repetition frequency of 200 kHz, a pulse width of 143.9 ps, and a spectrum width of 0.39 nm. The amplified pulse had quite good beam quality with Mx2 = 1.09 and My2 = 1.14.

10-mJ 300-fs 1-kHz cryogenically cooled Yb:CaF2 regenerative amplifier

In this paper, we report on a cw-pumped cryogenically cooled Yb:CaF2 laser crystal regenerative amplifier that can produce >10.3 mJ, <285 fs laser pulses at 1034-nm and repetition rate of 1-kHz. We achieve record high optical pump to optical amplified compressed output efficiency at >14%. Using a symmetric cavity design to compensate thermal lensing effect, we were able to achieve excellent beam quality with measured M2 at 1.19 and 1.16 at horizontal and vertical directions, respectively.

High power and excellent beam quality rod Yb: YAG regenerative amplifier

High power and excellent beam quality rod Yb: YAG regenerative amplifier

High-energy, low-jitter, narrowband ps probe laser for kHz-rate fs/ps coherent anti-Stokes Raman scattering.

Hybrid fs/ps coherent anti-Stokes Raman scattering (CARS) thermometry often utilizes ps probe pulses derived from pulse shaping or spectrally filtering the primary laser source or by synchronization with a low repetition rate external laser. This results in limited energy, spectral resolution, and/or repetition rate of the ps probe. In this work, a master-oscillator power-amplifier (MOPA) laser was synchronized to the oscillator of a Ti:sapphire regenerative amplifier to achieve high-energy (600 µJ), narrowband (58 ps) probe pulses at kHz repetition rates. Temporal filtering allows the pulse characteristics to be adjusted for each application. At 25 Torr, relevant to high-speed flows, the kHz-rate MOPA system generated signal-to-noise ratios 3× higher in nitrogen and had improved precision relative to a 10 ps probe derived from spectral filtering and the power-amplifier. The MOPA system also enabled single-shot ro-vibrational hybrid fs/ps CARS thermometry in 650 K heated air.

12-mJ 1-kHz cryogenically cooled rod Yb:YAG regenerative amplifier

We report on a continuous-wave (CW) pumped cryogenically cooled rod Yb:YAG regenerative amplifier delivering uncompressed 12-mJ, 90-ps, 1030-nm pulses at a 1-kHz repetition rate. The amplifier demonstrates an efficiency of 31.7%. A symmetric cavity design was utilized to compensate for the substantial thermal lensing effect, yielding a final measured beam quality of 1.1 in both horizontal and vertical directions. After significant gain narrowing, the measured spectra exhibit a bandwidth of 0.3 nm corresponding to an approximately 5 ps transform-limited pulse.

Sub-two-cycle intense pulse generation based on two-stage hollow-core fiber compression using an ytterbium amplifier

We demonstrate the generation of sub-two-cycle intense laser pulses based on two-stage hollow-core fiber (HCF) compression in a compact setup (footprint of 0.65 m × 2.85 m) using a commercial Yb:KGW regenerative amplifier. Spectrally broadened laser pulses with an output power of 7.2 W from the second HCF stage are compressed down to 6.6 fs (1.9 cycles at 1030 nm) using a pair of chirp mirrors and a pair of wedges with an efficiency of 86%, leading to a compressed output of 6.2 W. A pulse-to-pulse energy stability of 0.17% is measured for 10 min.

Compact 56 mJ thin-disk regenerative amplifier with thermally-near-unstable resonator structure

We experimentally demonstrated a very compact Yb:YAG thin-disk regenerative amplifier with hundred millijoules output potential. The cavity was designed based on the thermal-near-unsteady resonator concept with a cavity length of only 2 m. Laser outputs of 205 W for continuous wave, 156 W (3.1 mJ) for pulsed waves at 50 kHz, and 56 W (56 mJ) for pulsed waves at 1 kHz were achieved. To the best of our knowledge, this is the shortest cavity length reported for a thin-disk regenerative amplifier with a thermally-nearly-unstable resonator and the first time a pulsed-wave output has been achieved. This compact hundred-millijoule-class thin-disk regenerative amplifier allows for a significant simplification of the resonator structure and thus improves the environmental suitability of the system.

Self-injection-locked thin-film regenerative laser amplifier

Organic lasers based on distributed feedback (DFB) microcavities have been extensively investigated. However, the application of these lasers is limited by their low output power and large beam divergence. Therefore, laser amplifiers are needed to achieve practically applicable laser intensity and controllable lasing modes for far-field applications. In this work, we report self-injection-locked laser amplifiers using the combination of a DFB microcavity and a Bragg reflector, where a high-reflection mirror acts as the Bragg reflector and its feedback supplies the external-cavity injection. The coherent coupling between the DFB microcavity and the Bragg amplifier is crucial for achieving high conversion efficiency and high-contrast transverse modes. An amplification factor larger than 20 and a single output laser spot with high contrast that has been achieved. Such an integration design of the self-injected DFB microcavity amplifier can be directly utilized in the realization of high-performance thin-film laser sources for practical applications.

Nonlinear Generation, Compression and Spatio‐Temporal Analysis of sub‐GV/cm‐Class Femtosecond Mid‐Infrared Transients

AbstractA Yb:YAG thin‐disk regenerative amplifier with 3 kHz repetition rate pumps a second‐order nonlinear mixing scheme providing femtosecond transients of maximum electric field strength beyond 330 MV cm−1 at a center frequency of 45 THz. This value surpasses field conditions present at submolecular dimensions of matter. The inherent competition between efficiency and bandwidth in parametric downconversion is overcome with a third‐order nonlinear step of self‐phase modulation (SPM). The high repetition rate, versatility, beam quality, and passive phase stability of our system support advanced spectroscopic approaches like electro‐optic sampling (EOS). With this technique, solitonic self‐compression and octave‐spanning supercontinua directly on a subcycle scale are studied.

Frequency-mode-stable regenerative amplification at terahertz burst rates

Generation of high-fidelity amplified pulse bursts with a regular interpulse interval yields, in the spectral domain, an equidistant pattern of narrowband spectral modes, similar to frequency combs produced by cw mode-locked lasers but with greatly increased pulse energy. Despite their great potential for nonlinear spectroscopy, material processing, etc., such long frequency-stable bursts are difficult to generate and amplify because of prominent temporal intensity modulation even after strong dispersive pulse stretching. This study presents a burst generation method based on a master-oscillator regenerative-amplifier system that allows for chirped-pulse amplification (CPA) with high scalability in pulse number. A gradual smoothing of temporal intensity profiles at an increasing number of pulses is discovered, demonstrating an unexpected recovery of the CPA performance at terahertz intraburst repetition rates. In consequence, a self-referenced stable burst spectral peak structure with megahertz peak width is generated without risk of amplifier damage caused by interference of chirped pulses. This result eliminates limitations in burst amplification and paves the way for advancements in ultrashort-pulse burst technology, particularly for its use in nonlinear optical applications.

Intracavity frequency doubling acousto-optic Q-switched high repetition rate high-energy Nd:YLF laser.

The ongoing advancement of Ti:sapphire femtosecond laser technology has drawn increasing attention to high repetition rate, high-energy green lasers as ideal pump sources for Ti:sapphire regenerative amplifiers. This study employed a neodymium-doped yttrium lithium fluoride (Nd:YLF) as the gain medium, supplemented with side-pumped laser diodes, acousto-optic Q-switching, and intracavity frequency doubling technologies. The results demonstrated a repetition rate ranging from 1-10kHz, a pulse width of less than 100ns, and a single pulse energy exceeding 50mJ at 527nm green light output. Furthermore, an operating stability (RMS) of ≤0.15% was maintained for 14h at a repetition rate of 1kHz and an output power of 40W.

Unaveraged simulations of a cavity based free electron laser

The computer simulation of a cavity-based (oscillator) Free-Electron Laser (FEL) requires the modelling of both the electron-light interaction in the FEL undulator and the radiation propagation within the optical cavity. The unaveraged 3D FEL simulation code Puffin has been coupled with the Optical Propagation Code (OPC) to allow a broadband, high temporal-resolution cavity FEL to be modelled for the first time. This requires the translation of the radiation field formats between the Puffin and OPC codes. This translation is described and the coupled codes are then used to model an example of a Regenerative Amplifier FEL operating in the VUV.

A Sub-Picosecond Laser System Based on High-Energy Yb:YAG Chirped-Pulse Regenerative Amplification

In this study, we have successfully demonstrated a high-energy subpicosecond Yb:YAG laser system based on chirped-pulse regenerative amplification. Our experimental results demonstrate a pulse energy of 3 mJ with a pulse duration of 829.8 fs and a repetition rate of 1 kHz. Additionally, we conducted an extensive investigation into the system’s recompression capability under various modulation and seeding conditions. Our findings suggest that the system can achieve effective recompression over a broad range of parameters, with the ability to compensate for a considerable degree of chirp. Our study provides valuable insights into the fundamental physic of high-energy laser systems and the performance characteristics of chirped-pulse regenerative amplification.