Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The Research Centre Dresden-Rossendorf is planning to build a fully diode-pumped Petawatt laser based on Ytterbium-doped calcium fluoride. A pulse energy of 200J, a repetition rate of 1Hz and a pulse duration of 200fs after compression are desired. In this project a total pump peak-power of 1.5MW is scheduled assuming a pump pulse duration of 2ms and a targeted optical-to-optical conversion efficiency of 10%. Here we present gain measurements and time-resolved analysis of the thermal lens of different Yb:CaF2 amplifier configurations. 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. Therefore, a disk amplifier was compared with a rod laser. A pulse energy of 600mJ at a repetition rate of 1Hz was achieved using a cylindrical rod with a length of 20mm, a diameter of 28mm and an Yb-concentration of 2mol%. For seeding an Yb:YAG pre-amplifier produced pulses with a duration of 6ns. With a 2-disk Yb:CaF2 amplifier comprising of 8 extracting beams and a pump recovery configuration the minimum required pump fluence in order to bleach out re-absorption at the laser wavelength of 1030nm was reduced roughly by a factor of two down to 13J/cm². Furthermore, the thermal lens power was reduced from 5dpt of the rod down to smaller than 0.05dpt for 3mm thin disks at 10Hz.