4-WAVE MIXING IN CO VIA THE C1-SIGMA-+ (NU'=0) STATE

Coherent vacuum ultraviolet (VUV) radiation was generated by four-wave difference frequency mixing (ωVUV=2ω1-ω2) of pulsed dye laser radiation in carbon monoxide (CO). The frequency ω1 was tuned to the C1Σ+(υ′=0)←X1Σ+(υ″=0) two-photon transition, while the dye laser frequency ω2 was scaned around 17650 cm-1 which corresponds to the A1Π(υ=7)«C1Σ+(υ′=0) transition energy. The VUV intensity was found to be strongly wavelength dependent. The analysis of the spectrum revealed (i) that the VUV intensity was enhanced by the rotational levels of the A1Π(υ=7) state and (ii) that the off-resonance excitation in the C1Σ+(υ′=0)←X1Σ+(υ″=0) two-photon transition greatly contributed to the present four-wave mixing process. The effects of pumping laser detuning, saturation and foreign gases are briefly discussed. © 1990 Springer-Verlag.