Phase-matched second-harmonic generation is obtained in various LiInS<sub>2</sub> crystals by use of the tunable picosecond output of the free-electron laser for infrared experiments (FELIX) as the pump source in the mid-IR range from 2.75 to 6.0 µm. Deviations from the phase-matching curve calculated from Boyd's refractive-index data are observed. Furthermore, the optical damage threshold of the crystals has been measured to be 1.1. J/cm<sup>2</sup>(>6 GW/cm<sup>2</sup>) at the 5-µm wavelength. LiInS<sub>2</sub> holds great promise for parametric interaction in the 1–13-µm range.
© 2001 Optical Society of America
(140.2600) Lasers and laser optics : Free-electron lasers (FELs)
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.4400) Nonlinear optics : Nonlinear optics, materials
(320.7110) Ultrafast optics : Ultrafast nonlinear optics
G. M. H. Knippels, A. F. G. van der Meer, A. M. MacLeod, A. Yelisseyev, L. Isaenko, S. Lobanov, I. Thènot, and J.-J. Zondy, "Mid-infrared (2.75–6.0-µm) second-harmonic generation in LiInS2," Opt. Lett. 26, 617-619 (2001)