2-COLOR RESONANT 4-WAVE-MIXING SPECTROSCOPY OF AMMONIA

We demonstrate the use of two-color resonant four-wave mixing (TC-RFWM ) spectroscopy to detect gas-phase ammonia molecules. Appropriate choi ce of the two different excitation frequencies is shown to cause subst antial enhancement in the third-order susceptibility, (chi)(3)r and a consequent increase both in spectral sensitivity and in selectivity as compared with the corresponding one-color degenerate four-wave mixing (DFWM) technique.