Abstract

Continuous-wave (cw), narrow-bandwidth lasers that are tunable in the mid-IR wavelength range are important for analytical applications. The primary laser sources for this wavelength region include color-center as well as lead-salt diode lasers. Wide tunability can be achieved by difference-frequency mixing. Good results are obtained with LiNbO₃ by using collinear 90° phase matching and temperature tuning. We achieved tuning between 2.4 µm and 3.6 µm and cw output powers of several microwatts by mixing cw dye- (Rh 6G) and 488 nm Ar⁺-laser radiation in LiNbO₃. The required range of temperature was 230–400°C. The wavelength region beyond 4 µm can be accessed with new solid-state lasers and optical nonlinear materials. The design options of novel tunable cw IR laser systems based on difference-frequency mixing at near-room temperature in AgGaS₂ or AgGaSe₂ will be discussed. For AgGaS₂, the mixing of Ti:sapphire- and dye-laser radiation permits tunability of 3.85–9.1 µm with a higher figure of merit than for LiNbO₃. Furthermore, the wavelength can be extended to 12 µm by using AgGaSe₂, which exhibits the highest figure of merit in this region. This can be accomplished, for example, by mixing cw single-frequency 1.32 µm Nd:YAG and NaCl:OH color-center laser radiation. The temperature-stability and damage-threshold issues were examined carefully for both new nonlinear optical materials.

© 1990 Optical Society of America