Watt-class optical parametric amplification driven by a thulium doped fiber laser in the molecular fingerprint region

Numerous molecules important for environmental and life sciences feature strong absorption bands in the molecular fingerprint region from 3 mm-20 mm. While mature drivers at 1 mm wavelength are the workhorse for the generation of radiation up to 5 mm (utilizing down-conversion in nonlinear crystals) they struggle to directly produce radiation beyond this limit, due to impeding nonlinear absorption in non-oxide crystals. Since only non-oxide crystals provide transmission in the whole molecular fingerprint region, a shift to longer driving wavelengths is necessary for a power scalable direct conversion of radiation into the wavelength region beyond 5 mm. In this contribution, we present a high-power single-stage optical parametric amplifier driven by a state of the art 2 mm wavelength, thulium-doped fiber chirped pulse amplifier. In this experiment, the laser system provided 23 W at 417 kHz repetition rate with 270 fs pulse duration to the parametric amplifier. The seed signal is produced by supercontinuum generation in 3 mm of sapphire and pre-chirped with 3 mm of germanium. Combining this signal with the pump radiation and focusing it into a 2 mm thick GaSe crystal with a pump intensity of 160 GW/cm2 lead to an average idler power of 700 mW with a spectrum spanning from 9 mm-12 mm. To the best of our knowledge, this is the highest average power reported from a parametric amplifier directly driven by a 2 mm ultrafast laser in the wavelength region beyond 5 mm. Employing common multi-stage designs, this approach might in the future enable multi-watt high-power parametric amplification in the long wavelength mid infrared.