Research

Mid-infrared laser becoming increasingly important for high-harmonic generation (attosecond pulse), development of novel x-ray sources, and strong-field physics. Optical parametric chirped-pulse amplification (OPCPA) seems to be the most promosing approach to generate high power midinfrared pulses, i.e. few-cyle pulses with pulse energies in the mJ range at kHz repetition rates. However, powerful pump lasers are required.

To exploite the relatively high nonlinear coefficient of non-oxide crystals, such as ZnGeP2, the emitted wavelength of the pump sources have to be above 2 µm. This ensures that the absorption in the nonlinear crystals is significantly reduced. Here we concentrate our research on regenerative amplifiers using Ho:YLF as a gain medium with a central wavelenght of around 2050 nm. Pulse energies in the millijoule regime (~10 mJ) have been achieved directly from our regenerative amplifier which was conceptually designed as a ring cavity. With the entire setup shown in Fig. 1 we are able to generate pulse energies of up to 55 mJ at 1 kHz with very low pulse-to-pulse fluctuations (rms < 0.5 %).

Fig. 1. High power 2 µm laser delivering pulse energies of up to 55 mJ. The seed-source is a three-stage system consiting of a fs Er:fiber laser, a super-continuum highly nonlinear fiber and a Tm:fiber pre amplifier. After 24 round trips a state of operation is reached where the regenerative amplifier emits stable pulses (rms < 0.3 %) of around 10 mJ at 1 kHz. A booster (two Ho:YLF crystals) stage raises the pulse energy to > 50 mJ.