DEGENERATE 4-WAVE-MIXING FROM LASER-POPULATED EXCITED-STATES

Degenerate four-wave mixing (DFWM) from laser-populated excited states , i.e., two-step DFWM (2S-DFWM), has been performed to investigate the possibility of increasing signal quality (i.e., strength or signal-to -noise ratio) when species with low transition probabilities or far-UV transitions are to be detected or when large beam areas are used. Gol d atoms, aspirated into an air-acetylene flame, were chosen as a suita ble species for this investigation. The 2S-DFWM signal strength was fo und to be comparable to the ordinary (one-step) DFWM signals for moder ately high UV-light intensities but substantially better for low UV-li ght intensities. This finding implies that DFWM detection of species w ith lower transition probabilities in the first step as compared with gold (< 10(-8) s(-1)) can benefit from the 2S-DFWM technique when mode rate or low UV-light intensities are available. Additional possible ad vantages of using 2S-DFWM are also discussed.