Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

With the first demonstration of direct diode-pumped TW lasers with pulse energies of 1 J and more a scaling of this approach for use in PW-class laser systems became feasible. The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. In order to minimize the required pump peak power and therefore the initial costs a broad-band Ytterbium doped laser material with a long fluorescence lifetime (i.e. Yb:glass or Yb:CaF2) is chosen. A total pump peak-power of 1.2 MW is scheduled assuming a pump pulse duration of 2 ms and an envisioned optical-to-optical conversion efficiency of 10% before compression. Pulses as short as 60fs having an energy of 25nJ are generated in a commercial Yb:KGW oscillator at a center wavelength of 1035nm. In order to employ CPA technique the pulses are stretched to 2ns in a grating stretcher having grating constant of 1760 lines per mm. The amplifier-chain consists of a regenerative amplifier and 4 subsequent multipass amplifiers. While the regenerative amplifier produces a gain 40.000 gain narrowing is required to be suppressed by intra-cavity spectral shaping. In free-running mode (unseeded) a bandwidth of 20nm of the regenerative amplifier operating at the mJ level was achieved. A booster amplifier with a gain of 100 and 3 further multipass amplifiers each having a gain of 10-16 are required to achieve the desired pulse energy. Both, multipass amplification to the Joule-level and a small-signal of >40 in a single-disk Yb:CaF2 booster have been demonstrated recently.
For thermal management of the high-energy lasers the active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. In order to maintain both efficiency and repetition rate and to suppress parasitic lasing while scaling the aperture of disk amplifiers a multiple disk approach also employing pump-recycling was proposed. Time-resolved thermal lens investigations on a diode-pumped Yb:CaF2 disk revealed a one order of magnitude less impact on the wavefront abberations compared to a Yb:YAG disk having a similar geometry.
In this paper we introduce the basic design concepts and first experimental proofs of the fully diode-pumped high peak-power laser PEnELOPE.