Frequency modulation excitation spectroscopy

Excitation spectroscopy is performed using frequency modulated laser radiation with widely spaced sidebands to pump a resonant absorber. The excited upper state population, and hence the intensity of the incoherent fluorescence emitted, is found to be time domain modulated at the sideband spacing frequency. By monitoring the amplitude and phase of the fluorescence modulation as functions of laser carrier frequency and sideband spacing frequency, the absorption lineshape, dispersion lineshape, and upper state lifetime can be determined. © 1982.