Saturation effects in molecular spectroscopy using degenerate four‐wave mixing

Abstract

AbstractLineshapes of degenerate four‐wave mixing signals induced by both monochromatic and non‐monochromatic lasers are compared with predictions of the non‐perturbative model of Bratfalean, Lloyd and Ewart (BLE model) for the interaction of pump and probe beams of arbitrary intensity. Spectral lineshapes of isolated lines in DFWM spectra of OH in a methane–oxygen flame were recorded using a novel single‐mode tunable laser as a function of laser power. Power broadening of the lineshapes was found, in this case of an essentially monochromatic laser, to be well described by the BLE model. DFWM lineshapes of more complex molecular spectra were recorded in C2 in an oxy–acetylene flame using a standard, non‐monochromatic, dye laser. Lineshapes of closely spaced molecular resonances were found to be appreciably affected by saturation or power broadening effects. These effects were reasonably well approximated by the non‐perturbative BLE model when adapted to take account of the finite laser bandwidth. In contrast, the experimental lineshapes of the C2 spectra for saturating fields could not be modeled using the standard perturbative model of Abrams and Lind Copyright © 2003 John Wiley & Sons, Ltd.