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 ...

Max Planck Institute of Quantum Optics

Geometric scaling of a Kerr-lens mode-locked Yb:YAG thin-disk oscillator yields femtosecond pulses with an average output power of 270 W. The scaled system delivers femtosecond (210-330 fs) pulses with a peak power of 38 MW. These values of average and peak power surpass the performance of any previously reported femtosecond laser oscillator operated in atmospheric air.

Energy scaling of Kerr-lens mode-locked thin-disk oscillators.

A Kerr-lens mode-locked (KLM) Yb:YAG thin-disk oscillator delivering 215-fs pulses with 75-W average power and 1.4-MW peak power at a repetition rate of 260 MHz is presented. Self-starting KLM is demonstrated at an output power of 68 W. This is the highest repetition rate of any mode-locked thin-disk oscillators so far. Concepts for scaling the repetition rate up to 1 GHz are discussed.

260-megahertz, megawatt-level thin-disk oscillator.

A highly-dispersive mirror with the unprecedented group delay dispersion of -10000 fs<sup>2</sup> in the wavelength range of 1025-1035 nm is reported. Reproducible production of a coating with such a high dispersion was possible due to the recently developed robust synthesis technique. Successful employment of the new highly-dispersive mirror in an oscillator is demonstrated.

Highly-dispersive mirrors reach new levels of dispersion.

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.

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

A power-scalable concept for carrier-envelope-phase stabilization is presented. It takes advantage of simultaneous pumping of the zero- and first-phonon absorption line of Yb:YAG at 969 and 940 nm. The concept was implemented to lock the carrier-envelope-offset frequency of a 45 W average power Kerr-lens mode-locked thin-disk oscillator. The lock performance is compared to previous experiments where carrier-envelope-stabilization was realized by means of cavity loss modulation.

Carrier-envelope-phase stabilization via dual wavelength pumping.

Spectral broadening in bulk material is a simple, robust and low-cost method to extend the bandwidth of a laser source. Consequently, it enables ultrashort pulse compression. Experiments with a 38 MHz repetition rate, 50 W average power Kerr-lens mode-locked thin-disk oscillator were performed. The initially 1.2 μJ, 250 fs pulses are compressed to 43 fs by means of self-phase modulation in a single 15 mm thick quartz crystal and subsequent chirped-mirror compression. The losses due to spatial nonlinear effects are only about 40 %. A second broadening stage reduced the Fourier transform limit to 15 fs. It is shown that the intensity noise of the oscillator is preserved independent of the broadening factor. Simulations manifest the peak power scalability of the concept and show that it is applicable to a wide range of input pulse durations and energies.

All solid-state spectral broadening: an average and peak power scalable method for compression of ultrashort pulses.

We have recently demonstrated a simple power scaling procedure for Kerr-lens mode-locked thin-disk oscillators. Here we report on the extension of this scheme to a broadband high-peak-power thin-disk oscillator, delivering 140-fs pulses with a peak and average power of 62 MW and 155 W, respectively. This result shows that reaching the emission bandwidth of the gain material in Kerr-lens mode-locked thin-disk oscillators is feasible without sacrificing output power, efficiency, or stability by relying on high intracavity nonlinearities.

Powerful 100-fs-scale Kerr-lens mode-locked thin-disk oscillator.

We report on a laser system based on thin-disk technology and chirped pulse amplification, providing output pulse energies of 200 mJ at a 5 kHz repetition rate. The amplifier contains a ring-type cavity and two thin Yb:YAG disks, each pumped by diode laser systems providing up to 3.5 kW power at a 969 nm wavelength. The average output power of more than 1 kW is delivered in an excellent output beam characterized by M<sup>2</sup>=1.1. The output pulses are compressed to 1.1 ps at full power with a pair of dielectric gratings.

1  kW, 200  mJ picosecond thin-disk laser system.

Peak and average power scalability is the key feature of advancing femtosecond laser technology. Today, near-infrared light sources are capable of providing hundreds of Watts of average power. These sources, however, scarcely deliver pulses shorter than 100 fs which are, for instance, highly beneficial for frequency conversion to the extreme ultraviolet or to the mid- infrared. Therefore, the development of power scalable pulse compression schemes is still an ongoing quest. This article presents the compression of 90 W average power, 190 fs pulses to 70 W, 30 fs. An increase in peak power from 18 MW to 60 MW is achieved. The compression scheme is based on cascaded phase-mismatched quadratic nonlinearities in BBO crystals. In addition to the experimental results, simulations are presented which compare spatially resolved spectra of pulses spectrally broadened in self-focusing and self-defocusing media, respectively. It is demonstrated that balancing self- defocusing and Gaussian beam convergence results in an efficient, power-scalable spectral broadening mechanism in bulk material.

Jonathan Brons

Max Planck Institute of Quantum Optics

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