Multifrequency sum-frequency generation of Q-switched CO laser radiation in a BaHgGeSe4 crystal

We report an experimental study of sum-frequency generation of a broadband Q-switched CO laser (λ ≈ 5–6 μm) in a new nonlinear biaxial BaHgGeSe₄ crystal for four types of phase matching in the xz plane with varying polar and azimuthal angles of the crystal. The sum-frequency generation spectrum contains over 200 spectral lines in the wavelength range from 2.5 to 2.8 μm, with a power maximum near 2.6 μm. An evaluation of the efficiency of various interaction types shows that, in this crystal, sum-frequency generation with the oo–e phase matching type in the crystal orientation in question is most effective. Its efficiency exceeds that of similar processes with ee–o and eo–o phase matching by ∼4.1 and 3.8 times, respectively.