Abstract

Difference-frequency mixing of high-power near-IR laser diodes is an attractive technique for generation of broadly tunable coherent mid-infrared radiation. Such sources can be compact and operate at room temperature, giving them broad potential application to spectroscopy and chemical sensing. Mid-infrared generation by difference-frequency mixing (DFM) of laser-diode wavelengths has been demonstrated by noncritical birefringent phase matching in AgGaS₂ and AgGaSe₂¹ and by quasi phase matching (QPM) in LiNbO₃ waveguides.^2,3 LiNbO₃ is a robust, inexpensive, and highly reliable nonlinear material for DFM, and QPM permits the material to be tailored to mix arbitrary laser-diode wavelengths by choice of the ferroelectric domain reversal period. Recent advances in electric-field poling of LiNbO₃ material allows QPM to be implemented in bulk interactions, and it has been used for mid-IR optical parametric oscillation.^4,5 In this work we demonstrate the generation of tunable 3.6–4.0-μm radiation by QPM-DFM in electric-field-poled bulk LiNbO₃ by using two high-power, single-spatial-mode tunable laser-diode sources at wavelengths near 780 nm and 980 nm. Mid-infrared conversion efficiencies up to 0.008% /W, which are comparable to values measured in AgGaS₂, are demonstrated.

© 1995 Optical Society of America