Predissociation dynamics studied by degenerate four wave mixing spectroscopy

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When then laser frequency was tuned through the C-X two-photon transition of NO molecules, near-IR and UV radiation were emitted along the laser propagation direction within a narrow solid angle. It was shown that the UV wave was generated by the parametric four wave mixing (PFWM) process. Excitation spectra for the C-X band exhibited an excellent S/N ratio, implying that PFWM might be utilized as a novel spectroscopic method which can interrogate the two-photon resonant levels.Amplified spontaneous emission (ASE) from single rotational levels of several Rydberg states of NO has been investigated. The UV laser is fixed to a specific rotational component of the A state. When the second laser was introduced collinearly and the frequency was resonant to the transitions fromthe A state to the higher Rydberg members, the highly directional ASE in the near IR region was found to be generated along the excitation laser beams. Dispersed ASE spectra revealed the cascading radiative decay from the initially populated level down to the A state. It was demonstrated that ASE competes with weak predissociation.