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Mid-infrared laser generation at 4.7–5.1 μm of the Cr,Fe:Zn1-xMgxSe (x ≈ 0.4) single crystal under various excitation wavelengths

The cryogenically cooled Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.4) single crystal with the thickness of ~3.6 mm was investigated under two different excitation wavelengths of the Q-switched Er:YAG laser (λ ≈ 2.94 μm, Eout ≈ 50 mJ) and by the gain-switched Fe:ZnSe laser (λ ≈ 4.05 μm, Eout ≈ 9 mJ). Because of relatively low Fe2+ ions concentration, the absorption coefficients at 78 K and 300 K ranged between 3 cm-1 and 2 cm-1 for both excitation wavelengths used. Absorption and fluorescence spectra, fluorescence lifetime as well as laser output characteristics were measured at low temperatures (78–180 K). The Cr,Fe:Zn1-xMgxSe (x ≈ 0.4) laser system was able to generate laser radiation at ~5 μm at liquid nitrogen (LN2) temperature of 78 K under both ~2.94 μm and ~4.05 μm laser excitation. The laser oscillation wavelength was shifted up to ~5 μm compared with a typical Fe:ZnSe output (~4.0–4.1 μm at LN2 temperature) due to the high amount of magnesium in the host material. Moreover, the oscillation wavelength was shifted even farther by increasing temperature of the active medium. The laser output energy was ~1.34 mJ and ~0.14 mJ for the ~2.94 μm and ~4.05 μm laser excitation, respectively. The beam profile structure was approximately fundamental for both excitation wavelengths used. The results present a novel mid-infrared 4.7–5.1 μm coherent laser source based on cubic AIIBVI matrix using direct excitation at wavelengths of ~2.94 μm or ~4.05 μm.