Development of microwave-optical double-resonance spectroscopy using a Fourier-transform microwave spectrometer and a pulsed laser

A new type of microwave-detected microwave-optical double-resonance (MODR) spectroscopy has been developed using a Fourier-transform microwave spectrometer and a tunable pulsed dye laser. In this method, a free-induction decay (FID) signal was detected instead of the microwave (MW) absorption. To demonstrate the performance, we measured the MODR spectra of the CCS and C4H radicals in supersonic jets generated by a pulsed-discharge nozzle. Since the pulsed sources are employed for both the optical and microwave radiations, it is possible to control the relative timing of irradiations of the MW and optical pulses. We were able to obtain two different types of spectra; one is the ordinary population labeling spectrum, and the other is a spectrum obtained by breaking the coherence of molecules. In the latter case, more than 50% of depletion of the FID signal was observed, which is unable to be attained when noncoherent phenomena are used to detect the double-resonance signal. (C) 2002 American Institute of Physics.