DFG-based mid-IR tunable source with 0.5 mJ energy and a 30 pm linewidth

We report on a laser system based on difference frequency generation (DFG) to produce tunable, narrow-linewidth (<30 pm), and comparatively high-energy mid-IR radiation in the 6.8 μm region. The system exploits a lithium thioindate (LiInS2) nonlinear crystal and nanosecond pulses generated by single-frequency Nd:YAG and Cr:forsterite lasers at 1064 and 1262 nm, respectively. Two experimental configurations are used: in the first one, single-pass, the mid-IR energy achieved is 205 μJ. Additional increments, up to 540 μJ, are obtained by performing double-pass through the nonlinear crystal. This laser has been developed for high-resolution photon-hungry spectroscopy in the mid-IR.