YAG Thin-disk Regenerative Amplifier Research Articles

41 W, 206 fs regenerative amplifier based on CPA-free amplification of femtosecond pulses

We present a low-cost method to mitigate the gain narrowing effects during regenerative amplification based on a high-repetition-rate, high-power continuously pumped Yb:YAG thin disk regenerative amplifier (RA). By inserting a 1-mm-thick SiO2 plate on a certain position in the RA, the narrowed bandwidth of the amplified spectrum of 3 nm was significantly broadened to a root-mean-square (RMS) bandwidth of 6.9 nm, which reveals the effectiveness of the method. At a repetition rate of 200 kHz, an output power of 41 W was obtained with a compressed pulse duration of 206 fs. The amplifier displayed stability with a root-mean-square power noise as low as 0.46%. The optical resonator remained nearly diffraction-limited beam quality (M2 < 1.35) until the maximum output power.

Compact high-repetition-rate Yb:YAG thin-disk regenerative amplifier with fundamental transverse mode laser output

A compact thin-disk regenerative amplifier with a resonator length of less than 2.3 m operating at the edge of the stability zone, which provides the laser with high beam quality is reported. The resonator delivers the continuous wave output power of 80.03 W, beam quality Mx2 = 1.64, My2 = 1.5, and slope efficiency of 45.01% at a resonator length of 2067 mm. When the resonator length is 2297 mm, the output power of 58.97 W (1.18 mJ) at a 50 kHz repetition rate with a slope efficiency of 17.71% is achieved. At this condition, when the output power is 34.3 W at a 50 kHz repetition rate, a laser with beam quality Mx2 < 1.1, My2 < 1.1 is realized. When the resonator length is 2297 mm, an output power of 11.45 W (11.45 mJ) at 1 kHz repetition rate with beam quality Mx2 = 1.15, My2 = 1.22 and slope efficiency 5.35% is achieved. To the best of our knowledge, this is the first time that a Yb:YAG thin-disk regenerative amplifier has been reported to achieve a fundamental transverse mode laser output of more than 10 mJ with a resonator length of less than 2.3 m. Both theoretical analysis and preliminary experiments suggested that the thin-disk regenerative amplifier has the potential to achieve laser with more than 100 mJ with 1 kHz and good beam quality.

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.

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.

Beam mutation and its suppression in Yb:YAG thin-disk regenerative amplifiers

Beam mutation in thin-disk regenerative amplifiers is proposed here, to the best of our knowledge, for the first time. It is proved to appear together with period doubling bifurcation and deterministic chaos experimentally. The suppression of beam mutation is achieved by reducing the gate length of the regenerative amplifier. With the gate length of 1.88 μs, a Yb:YAG thin-disk regenerative amplifier with stable beam and single-energy pulse is realized. The maximum pulse energy is 145 mJ with the optical-optical efficiency of around 10 %. The repetition rate and the pulse width are 1 kHz and 580 ps respectively.

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

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.

Numerical and Experimental Analysis of Yb:YAG Thin Disk Regenerative Amplifier

We present an numerical and experimental analysis of a Yb:YAG thin disk regenerative amplifier. Group velocity dispersion, third order dispersion, and self-phase modulation (SPM) effects are considered in the simulations of the amplification process. By virtue of the simulations, a compact femtosecond Yb:YAG thin-disk chirped-pulse regenerative amplifier delivering an average power of 50 W at a central wavelength of 1030 nm with a propagation factor of M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <; 1.4 at a repetition rate of 200 kHz and a pulse duration of 500 fs was constructed. Numerical simulation based on this Yb:YAG thin-disk was carried out to investigate the pulse parameters evolution in each round trip. The measured experimental results in pulse width, spectrum, and pulse energy together fitted quite well with the numerical simulation. This plays an important role in the design of high-peak-power regenerative amplifier and will facilitate further power scaling and suppression of gain narrowing of the whole system.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier.

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

Direct regenerative amplification of femtosecond pulses to the multimillijoule level.

We present a compact femtosecond nonlinear Yb:YAG thin-disk regenerative amplifier delivering pulses carried at a wavelength of 1030nm with an average power of >200 W at a repetition rate of 100kHz and an energy noise value of 0.46% (rms) in a beam with a propagation factor of M2<1.4. The amplifier is seeded with bandwidth-limited subpicosecond pulses without temporal stretching. We give estimates for the nonlinear parameters influencing the system and show that chirped mirrors compress the 2mJ pulses to a near-bandwidth-limited duration of 210fs.

Self-compressed, spectral broadening of a Yb:YAG thin-disk amplifier.

We demonstrate pulse shortening of 1-ps Yb:YAG thin-disk regenerative amplifier to 500 fs by cross-polarized wave generation (XPW) in a 6 mm BaF2 crystal. The process is self-compressed and has 8.5% conversion efficiency corresponding to 18 µJ energy. Our theoretical and experimental investigation shows that the factor of 3 spectral broadening and pulse shortening in ps-XPW-generation only happens in unsaturated regime. We demonstrate that the initial spectral chirp affects the spectral broadening and pulse shortening of XPW pulses.

High-power, 1-ps, all-Yb:YAG thin-disk regenerative amplifier.

We report a 100 W, 20 mJ, 1-ps, all-Yb:YAG thin-disk regenerative amplifier seeded by a microjoule-level Yb:YAG thin-disk Kerr-lens mode-locked oscillator. The regenerative amplifier is implemented in a chirped pulse amplification system and operates at an ambient temperature in air, delivering ultrastable output pulses at a 5 kHz repetition rate and with a root mean square power noise value of less than 0.5%. Second harmonic generation of the amplifier's output in a 1.5 mm-thick BBO crystal results in more than 70 W at 515 nm, making the system an attractive source for pumping optical parametric chirped pulse amplifiers in the visible and near-infrared spectral ranges.

Thin disk amplifier-based 40 mJ, 1 kHz, picosecond laser at 515 nm.

We report on a frequency-doubled picosecond Yb:YAG thin disk regenerative amplifier, developed as a pump laser for a kilohertz repetition rate OPCPA. At a repetition rate of 1 kHz, the compressed output of the regenerative amplifier has a pulse duration of 1.2 ps and pulse energy of 90 mJ with energy stability of σ < 0.8% and M2 < 1.2. The pulses are frequency doubled in an LBO crystal yielding 42 mJ at 515 nm.

Yb:YAG thin-disk chirped pulse amplification laser system for intense terahertz pulse generation.

We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 µJ of energy were generated by means of optical rectification in an Mg-doped LiNbO3 crystal.

Wear-reducing Surface Functionalization of Implant Materials Using Ultrashort Laser Pulses

The aim of the project called “EndoLas” is the development of a reproducible and reliable method for a functionalization of articulating surfaces on hip joint endoprostheses due to a reduction of abrasion and wear by the generation of micro structures using ultrashort laser pulses. On the one hand, the microstructures shall ensure the capture of abraded particles, which cause third-body wear and thereby increase aseptic loosening. On the other hand, the structures shall improve or maintain the tribologically important lubricating film. Thereby, the cavities serve as a reservoir for the body's own synovial fluid. The dry friction, which promotes abrasion and is a part of the mixed friction in the joint, shall therefore be reduced. In experimental setups it was shown, that the abrasive wear can be reduced significantly due to micro-structuring the articulating implant surfaces.To shape the fine and deterministic cavities on the surfaces, an ultra-short pulsed laser, which is integrated in a high-precision, 5-axes micro-machining system, was used. The laser system, based on an Yb:YAG thin-disk regenerative amplifier, has an average output power of 50W at the fundamental wavelength of 1030nm, a maximum repetition rate of 400kHz and a pulse duration of 6 ps. Due to this, a maximum pulse energy of 125μJ is achievable. Furthermore external second and third harmonic generation enables the usage of wavelengths in the green and violet spectral range.

Optimization of beam quality and optical-to-optical efficiency of Yb:YAG thin-disk regenerative amplifier by pulsed pumping

We demonstrate an optimization method of beam quality and optical-to-optical (O-O) efficiency by using pulsed pumping. By changing the pulse duration and the peak intensity of pump pulse at the repetition rate of 1kHz, the beam quality and O-O efficiency of the Yb:YAG thin-disk regenerative amplifier can be improved. We applied this method to the regenerative amplifier under the pumping wavelength of both 940 and 969nm, and found that the method was effective in both pumping wavelengths. Although a Yb:YAG thin disk soldered on a copper tungsten heat sink, which has poor thermal properties compared with a thin disk mounted on a diamond substrate, was applied as a gain media, we obtained 45mJ output with 19.3% O-O efficiency and nearly diffraction-limited beam.

Few-cycle OPCPA system at 143 kHz with more than 1 μJ of pulse energy

We present an OPCPA system delivering 8.8 fs (3.3 optical cycles) pulses with 1.3 microJ of energy at 143 kHz repetition rate. Pump and seed for the parametric amplification are simultaneously generated by a broadband Ti:sapphire oscillator. The spectral components beyond 1000 nm are separated and amplified in an Yb:YAG thin-disk regenerative amplifier. The pulses are characterized using autocorrelation and SPIDER apparatus. With a pulse peak power of nearly 130 MW, the system is well-suited for future table top strong field experiments.