Two-stage, triple-pass 5-mJ-level Fe:ZnSe chirped-pulse amplifier with a KTA-based OPA frontend and flashlamp-pumped erbium lasers.

The development of Fe:ZnSe-based mid-infrared laser amplification as an alternative to optical parametric chirped-pulse amplification has become increasingly important in high-intensity laser science, especially for high-harmonic generation toward higher photon energies. Here, we demonstrate a Fe:ZnSe chirped-pulse amplification architecture that combines a KTiOAsO4-based optical parametric amplifier (OPA) frontend providing 29-μJ, 4-μm seed pulses, flashlamp-pumped erbium lasers as high-pulse-energy 3-μm-class pump sources, and cladding-assisted suppression of transverse parasitic oscillation in the Fe:ZnSe crystals. The system delivers 4.1-μm pulses at 5 Hz with an amplified energy of 6.7 mJ, a compressed energy of 4.7 mJ, and a pulse duration of 240 fs, while maintaining good beam quality and preserving an energy contrast of approximately 5000 in the amplified output. These results show that high-contrast, millijoule-level femtosecond Fe:ZnSe amplification can be achieved even with free-running flashlamp-pumped erbium lasers by reducing the required gain and number of passes through high-energy seeding. The demonstrated architecture provides a practical route toward further energy scaling of Fe:ZnSe-based 4-μm femtosecond lasers, ultimately aiming at terawatt-class peak powers with larger-aperture homogeneous crystals.