František Batysta

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.

ELI-Beamlines laser systems: status and design options

We present an overview of the projected and/or implemented laser systems for ELI-Beamlines. The ELI-Beamlines facility will be a high-energy, high repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition rate laser pulses, and kilojoule nanosecond laser pulses that will be used for generation of 10 PW, and potentially higher, peak power. These systems will allow meeting user requirements for cutting-edge laser resources for programmatic research in generation and applications of high-intensity X-ray sources, in electron and proton/ion acceleration, and in dense plasma and high-field frontier physics.

Broadband OPCPA system with 11 mJ output at 1 kHz, compressible to 12 fs

We report on a broadband OPCPA system, pumped at 515 nm by frequency doubled Yb:YAG thin disk lasers. The system delivers 11.3 mJ pulses at a central wavelength of 800 nm with a spatial beam quality of M2 = 1.25 and > 25% pump-to-signal conversion efficiency. The broadband pulses were demonstrated to be compressible to 12 fs using a chirped mirror compressor.

Pulse synchronization system for picosecond pulse-pumped OPCPA with femtosecond-level relative timing jitter

A simple and compact scheme for synchronization of the pump and signal pulses for short-pulse OPCPA is demonstrated. Relative timing jitter of 17 fs RMS is achieved (1% of the pump pulse duration) and the system remains locked for hours. The scheme uses a balanced optical cross correlator to detect relative delays between the pump and signal pulses and can be operated with just 10s of μJ of pump energy and pJ-level signal energies.

Thin disk picosecond pump laser for jitter stabilized kHz OPCPA

We report on the initial performance of the first ELI-Beamlines high repetition rate, thin disk-based OPCPA pump laser. The laser is designed to produce a pulse train with pulse energies of 10-30 mJ at a 1 kHz repetition rate and is intended to be used as a pump source for an OPCPA amplifier. While the preliminary tests and analysis show that these target energies are well within the capabilities of the equipment available, the output energies of the current design are limited by self-phase modulation. We discuss the sources of this modulation and a new amplifier design to reduce these nonlinear effects. The efficiency of the second harmonic conversion of the thin disk amplifier output is measured to be higher than 65% and scaling to higher energies is discussed.

Multi-channel, fiber-based seed pulse distribution system for femtosecond-level synchronized chirped pulse amplifiers

We report on the design and performance of a fiber-based, multi-channel laser amplifier seed pulse distribution system. The device is designed to condition and distribute low energy laser pulses from a mode-locked oscillator to multiple, highly synchronized, high energy amplifiers integrated into a laser beamline. Critical functions such as temporal pulse stretching well beyond 100 ps/nm, pulse picking, and fine control over the pulse delay up to 300 ps are all performed in fiber eliminating the need for bulky and expensive grating stretchers, Pockels cells, and delay lines. These functions are characterized and the system as a whole is demonstrated by seeding two high energy amplifiers in the laser beamline. The design of this system allows for complete computer control of all functions, including tuning of dispersion, and is entirely hands-free. The performance of this device and its subsystems will be relevant to those developing lasers where reliability, size, and cost are key concerns in addition to performance; this includes those developing large-scale laser systems similar to ours and also those developing table-top experiments and commercial systems.

Jitter-compensated Yb:YAG thin-disc laser as a pump for the broadband OPCPA front-end of the ELI-Beamlines system

We report on a temporal jitter-compensated Yb:YAG thin-disc laser as a pump source for the front-end OPCPA of ELIBeamlines high energy and repetition rate system. The main advantage of using picosecond Yb:YAG thin-disc lasers is that relatively high energies in the kHz repetition rate range can be easily accessed. Although in our case the pump laser is optically synchronized to the OPCPA seeding Ti:Sapph laser, the stability of the OPCPA output gets heavily affected by delay jitter due to a large number of roundtrips in the regenerative amplifier cavity and slight ambient temperature drifts. Since interacting pulses are only ~1.5 ps in duration, an additional active stabilization of the pump path length corresponding to sub-100 fs delay precision must be implemented. In our work we demonstrate a novel design of a jitter stabilization system which employs a cross-correlation setup employing parametric amplification in two perpendicularly oriented nonlinear crystals. A small fraction of the OPCPA seed signal is being locked between cross-polarized and delayed replicas of a pump pulse. The feedback signal for the delay compensation is acquired by coupling the polarization-separated parts of the parametrically amplified signal into two channels of a balanced photodetector. The delay stabilization is achieved mainly by adjusting the cavity length of the regenerative amplifier with a piezo-mounted mirror. The proposed setup allows reducing the temporal jitter of Yb:YAG thin-disc regenerative amplifier to tens of fs RMS and maintaining it over extended periods of time.

Development of high energy, sub-15 fs OPCPA system operating at 1 kHz repetition rate for ELI-Beamlines facility

We report on the status of the high repetition rate, high energy, L1 laser beamline at the ELI-Beamlines facility. The beamline is based on picosecond optical parametric chirped pulse amplification (OPCPA) of pulses from a mode-locked Ti:Sapphire oscillator and has a target energy/repetition rate of 100 mJ/1 kHz with < 15fs pulse duration. The OPCPA pump lasers use thin disk technology to achieve the high energy and average power required to pump such a high energy, high repetition rate broadband amplifier. Here we report on the progress in beamline development and discuss the technical challenges involved in producing such a system and their solutions. A major focus of the laser development is reliable, robust operation and long term stability; mechanical, optical, and control system architecture design considerations to achieve our goals of long term stability are discussed.

Active cavity stabilization for high energy thin disk regenerative amplifier

We present an active cavity pointing stabilization system based on a novel method that tracks the cavity mode position directly on the thin disk gain medium itself. Here, the overlap of the lasing cavity with the pump, visible as a depletion within the pumped area, is most crucial to the stability of the laser. Short term stability as well as long term stability are significantly increased enabling day long operation, directly from a cold start of the laser system, without the need for thermalization and manual alignment.

Front end for high-repetition rate thin disk-pumped OPCPA beamline at ELI-beamlines

The ELI-Beamlines facility, currently under construction in Prague, Czech Republic, will house multiple high power laser systems with varying pulse energies, pulse durations, and repetition rates. Here we present the status of a high repetition rate beamline currently under construction with target parameters of 20 fs pulse duration, 100 mJ pulse energy, and 1 kHz repetition rate. Specifically we present the Yb:YAG thin disk lasers which are intended to pump picosecond OPCPA, synchronization between pump and signal pulses in the OPCPA, and the first stages of OPCPA.