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Abstract
Lasers operating in the middle infrared region are crucial for free-space communication, sensing, spectroscopic, biomedical, and defense-related applications. Transition-metal-doped II-VI compounds, particularly Cr- and Fe-doped materials, are key materials for mid-IR lasers operating in the 2–5 μm range. However, producing high-quality transition metal-doped ZnSe crystals is challenging due to limitations in conventional doping methods. This study first investigates the fabrication of transparent ZnSe ceramics via spark plasma sintering (SPS). The "green body" was fabricated by grinding chemical vapor deposition (CVD) polycrystalline ZnSe into sub-micron powders. Sintering was performed at pressures up to 90 MPa and temperatures up to 1200 °C under a vacuum with argon gas purging. The resulting ceramics achieved up to 99.9% density relative to single crystals with transmission >50% at 14.5 µm wavelength. Successful fabrication of transparent ZnSe ceramics demonstrates the viability of SPS as a method for producing TM-doped ceramics as gain media for mid-IR laser applications.
Additionally, we present numerical modeling and experimental characterization of a room-temperature, sub-nanosecond, gain-switched (GS) Fe:ZnSe laser operating at mid-infrared (mid-IR) wavelengths of 4.4–4.8 μm, pumped by two custom-built lasers. Utilizing a flashlamp-pumped, electro-optically (EO) Q-switched Cr:Er:YSGG laser at 2.79 μm with a 52 ns pulse duration and employing a La₃Ga₅SiO₁₄ (LGS) crystal-based Q-switch, we achieved single-spike pulses with output energies up to 0.39 mJ from 6.67 mJ of pump energy and a maximum temporal compression of 46 times compared to the pump pulse. Furthermore, pumping with a 2.98 μm idler from a KTiOAsO₄ (KTA) optical parametric oscillator (OPO), driven by a 9 ns, 1064 nm Nd:YAG laser, yielded single pulses of 1.05 mJ from 16 mJ pump energy. Pulse durations as short as 1.1 ns and 0.7 ns were recorded under excitation from the Cr:Er:YSGG and KTA-OPO systems, respectively. The numerical modeling showed good agreement with experimental results. Further optimization based on updated gain-switched model suggests that an Fe:ZnSe microchip laser configuration could be realized with a pulse duration of approximately 250 ps and an efficiency of ~20%. These findings highlight the significant potential of Fe:ZnSe lasers for diverse mid-IR laser applications.