Multiphoton resonances in the modulated fluorescence from an inhomogeneously broadened medium.
We consider the interaction of a fully amplitude-modulated, narrow-band laser with a strongly inhomogeneously broadened two-level medium and show that harmonics of the fluorescence of susceptibility, unlike the time-averaged fluorescence, retain the characteristic multiphoton resonance structure that is found in the absence of inhomogeneous broadening. This behavior correlates with the existence of double branches of the corresponding Bloch-Siegert resonance curves. For strong fields, the depth of modulation and the phase shift of the lowest fluorescence harmonic may deviate significantly from the results for weak, broadband excitation.
Ruyten
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