Investigation on laser-induced damage threshold of polycrystalline Fe:ZnSe with nanosecond-pulse-width pumping

• We report on a comparative investigation on the laser-induced damage threshold (LIDT) of polycrystalline Fe:ZnSe at its pump (2.82 μm) and emission (∼4.5 μm) wavelength with nanosecond pulse width for the first time. • The differences of the LIDT between the single-pass and lasing situations are examined, discussed and explained. • To test the LIDT of the Fe:ZnSe crystal at the interested wavelengths, we demonstrated two unique lasers: 2.82 μm KTA OPO and ∼4.5 μm room-temperature Fe:ZnSe laser. The slope efficiencies of the two testing lasers are the highest of their kinds, to the best of our knowledge. • The accurate LIDT is one of the key parameters for Fe:ZnSe crystals, which is important for designing high-energy, short-pulse-width Fe:ZnSe lasers. This paper presents a comparative investigation on laser-induced damage threshold (LIDT) of polycrystalline Fe:ZnSe pumped at 2.82 μm and ∼4.5 μm with pulse widths of several nanoseconds. The corresponding pump sources were a KTA optical parametric oscillator and a room-temperature Fe:ZnSe laser. The single-pass LIDTs at 2.82 μm (181 mJ, 8.0 ns) and ∼4.5 μm (53.4 mJ, 5.6 ns) were ∼1J/cm 2 (130 MW/cm 2 ) and ∼0.9 J/cm 2 (160 MW/cm 2 ), respectively. The LIDT decreased to an input peak power intensity of ∼0.48 J/cm 2 (60 MW/cm 2 ) at 2.82 μm if the Fe:ZnSe crystal was implemented in an oscillator during the lasing operation. The main reason that the Fe:ZnSe crystal was damaged at lower incident pump intensity was the higher intra-cavity intensity of the resonated ∼4.5 μm laser with shorter pulse width. The enhancement of the pump absorption and laser re-absorption increased the damage risk of the Fe:ZnSe crystal during the lasing operation. The LIDT of the Fe:ZnSe crystal is one of the key parameters for high-energy and high-intensity mid-infrared Fe:ZnSe lasers because it is the main limit for energy scaling.