CC BY
15LS-I-6
Progress in high-power, 100 kHz mid-infrared OPCPA's
M. Mero1
1Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, A3 Ultrafast Lasers and Nonlinear Optics, Berlin, Germany
Technologically mature, diode-pumped picosecond and sub-picosecond Yb lasers have become the main workhorses behind high-average-power, ultrafast optical parametric amplifiers (OPA's) operating in the near-infrared (0.8-3 |im) and at the short-wave edge of the mid-infrared (MIR, 330 |im). In the 1.5-4 |im spectral range, where various wide-bandgap oxide nonlinear optical crystals are commercially available, the exceptional power scalability of Yb lasers has already enabled average powers well beyond 10 W at multi-GW peak powers with pulses lasting only a few optical cycles [1]. Extension of the wavelength range above 5 |im is traditionally achieved by employing an OPA-DFG (difference frequency generation) cascade at an overall pump-to-MIR energy conversion efficiency of only < 0.5% at 8 |im. Using novel wide-bandgap non-oxide nonlinear crystals that can be pumped directly at ~1 |im without detrimental one- and two-photon absorption of pump radiation, the DFG step can be eliminated leading to a significant increase in the overall conversion efficiency and the attainable average and peak power beyond 5 ^m. Despite their utmost importance, properties of nonlinear optical crystals affecting OPA performance at repetition rates above a few kHz are rarely investigated or considered in the OPA design. Depending on the choice of crystal, such material properties can lead to a complicated interplay of thermal lensing, non-permanent photorefractive damage, and self- and cross-phase modulation of the interacting pulses. Here we review some of the important material properties of nonlinear optical crystals that can be employed in ultrafast, high-repetition-rate, Yb-laser-pumped MIR OPA's operating either below or above 4 |im and present examples of OPA's for each case [1,2].
References
[1] M. Mero, Z. Heiner, V. Petrov, H. Rottke, F. Branchi, G. M. Thomas, and M. J. J. Vrakking, "43 W, 1.55 ^m and 12.5 W, 3.1 ^m dual-beam, sub-10 cycle, 100 kHz optical parametric chirped pulse amplifier," Opt. Lett. 43, 5246 (2018).
[2] Z. Heiner, L. Wang, V. Petrov, and M. Mero, "Broadband vibrational sum-frequency generation spectrometer at 100 kHz in the 950-1750 cm-1 spectral range utilizing a LiGaS2 optical parametric amplifier," Opt. Express. 27, 15289 (2019).
