Refining the Performance of mid-IR CPA Laser Systems Based on Fe-Doped Chalcogenides for Nonlinear Photonics

The chirped pulse amplification (CPA) systems based on transition-metal-ion-doped chalcogenide crystals are promising powerful ultrafast laser sources providing access to sub-TW laser pulses in the mid-IR region, which are highly relevant for essential scientific and technological tasks, including high-field physics and attosecond science. The only way to obtain high-peak power few-cycle pulses is through efficient laser amplification, maintaining the gain bandwidth ultrabroad. In this paper, we report on the approaches for mid-IR broadband laser pulse energy scaling and the broadening of the gain bandwidth of iron-doped chalcogenide crystals. The multi-pass chirped pulse amplification in the Fe:ZnSe crystal with 100 mJ level nanosecond optical pumping provided more than 10 mJ of output energy at 4.6 mu m. The broadband amplification in the Fe:ZnS crystal in the vicinity of 3.7 mu m supports a gain band of more than 300 nm (FWHM). Spectral synthesis combining Fe:ZnSe and Fe:CdSe gain media allows the increase in the gain band (similar to 500 nm (FWHM)) compared to using a single active element, thus opening the route to direct few-cycle laser pulse generation in the prospective mid-IR spectral range. The features of the nonlinear response of carbon nanotubes in the mid-IR range are investigated, including photoinduced absorption under 4.6 mu m excitation. The study intends to expand the capabilities and improve the output characteristics of high-power mid-IR laser systems.