Tunable continuous-wave mid-infrared radiation by laser difference-frequency generation in LiInSe₂

We report on the first demonstration, to the best of our knowledge, of continuous-wave (cw) mid-infrared generation from laser difference-frequency mixing in a LiInSe₂ crystal (lithium indium selenide, or LiSe) in the X-Y plane. Two Ar⁺ laser-pumped Ti:sapphire lasers were employed as widely tunable pump sources. The phase-matching (PM) conditions in the cw difference-frequency generation (DFG) process have been investigated. Based on the measurements of relative values of the power conversion efficiencies for LiSe-and AgGaS₂-based DFG, the effective nonlinear coefficient d_eff of 12.1 pm/V for LilnSe₂ at ∼7 μm has been determined relative to the well known nonlinearity coefficient d₃₆ of AgGaS₂, which yields a power conversion efficiency of about 29.8 μW/(W².cm). The accessible infrared wavelength range is important for molecular spectroscopic studies and we will discuss the performance of this new laser source for trace gas sensing applications.