Degenerate four-wave mixing with a tunable excimer laser.

We use a simple, forward-geometry degenerate four-wave mixing setup to monitor weak absorptions of various gas-phase molecules with a tunable excimer laser. With this technique, state-selective detection of H(2), CO, H(2)O, and O(2) is demonstrated. The dependence of the forward-geometry degenerate four-wave mixing signals on various experimental parameters (e.g., pressure, laser power) is determined. Several mechanisms for the generation of the observed signals are discussed, including diffraction from density gratings or thermal gratings and two-photon degenerate four-wave mixing.