Abstract

In degenerate four-wave mixing, three input beams of identical frequency interact with a nonlinear medium to generate a fourth coherent signal beam. The efficiency is resonant with an atomic or molecular transition. The coherent nature of the signal beam offers many advantages for minor species detection. Prior experiments using ultraviolet wavelengths to detect OH or NH radicals in flames and NO as a low pressure gas readily demonstrated good background discrimination and high signal collection efficiency. The current experiments illustrate the potential of infrared DFWM for minor species detection. Extension of degenerate four-wave mixing to the infrared region of the spectrum offers exciting potential for species diagnostics. Many molecules are not easily detected using laser-induced fluorescence or multiphoton ionization because they do not have readily accessible and well characterized electronic absorptions. Almost all molecules have ro-vibrational transitions that are accessible using infrared light. However, detection of molecules using infrared diagnostic methods has often proved difficult.

© 1991 Optical Society of America