Discrete resonance CARS emission from NO2: Its temporal and spectral properties

Coherent anti-Stokes emission has been observed for resonance excitation of NO₂ within an optical pumping geometry similar to that employed for CARS spectroscopy. Spectra have been measured for excitation of NO₂ in three wavelength regions of its absorption: 585, 564, and 542 nm. These spectra have been used to investigate the four wave process which produces this emission and to determine the ro-vibronic contributions to the absorption of NO₂ at these wavelengths. Results from pressure quenching and time dependence studies indicate that a coherent level is produced which has a relatively long lifetime. The anti-Stokes emission has the same temporal properties as the Stokes pulse. This indicates that only the first pump photon is in resonance with an electronic transition. A comparison of these results with those expected for resonance Raman and discrete resonance Raman in particular indicates that the resonance CARS process can be interpreted by theoretical and phenomenological considerations developed to describe resonance Raman.