Population fluctuations in a two-level atom excited by a field with amplitude and phase noise

Gautam Vemuri, Michael H. Anderson, R. D. Jones +2 more

A.B. Kuznetsov, Smirnov A Yu

Helmut Ritsch, P. Zoller, J. Cooper

Variances and power spectra of the resonance fluorescence intensity induced by laser noise in two-level systems are studied theoretically. The effects of amplitude and phase noise fluctuations of a single-mode laser are investigated. Correlations of amplitude and phase fluctuations, as is relevant for excitation with diode lasers, are shown to lead to pronounced asymmetries in variance spectra.

M. H. Anderson, R. D. Jones, J. Cooper +4 more

We have measured the variance in fluorescence intensity and the spectrum of those fluctuations for two-level atoms in a phase-diffusing laser field. We compare our results with recent theoretical predictions that have been extended to include the effects of Doppler broadening and spatial variation of the laser intensity. Our study includes the effects of laser power, bandwidth, and shape (Lorentzian and non-Lorentzian) of the laser spectrum. At lower laser intensities, our measured variances versus detuning are in quantitative agreement with the theoretical predictions. At intensities above saturation, the variance is sensitive to inhomogeneities in the distribution of laser intensity in the interaction region, and only qualitative agreement is achieved. Asymmetries in the variance versus detuning resulting from correlated amplitude and phase noise have been observed. Spectra of the phase-noise-induced fluorescence-intensity fluctuations are shown to contain contributions from transients excited by the phase noise and are more sensitive to artifacts in the noise modulation process than the intensity spectrum of the laser field itself.

Th. Haslwanter, Helmut Ritsch, J. Cooper +1 more

Significant fluctuations, above the shot-noise limit, have been observed in the intensity of fluorescent light scattered from atoms excited by an intense noisy laser, where a central role is played by the nonlinearity of the atom-field interaction. By considering the variance of the atomic populations, we show that ``noise spectroscopy'' is sensitive to the field statistics of the laser. We specifically consider the cases of resonance fluorescence (analogous in the weak-field limit to analysis by a Fabry-P\'erot interferometer), two-photon excitation, and double optical resonance for variable laser intensity and bandwidth. We show that large differences in the ``noise'' spectra can occur between lasers characterized by a phase-diffusion or a phase-jump model, although these models would give the same values for the mean atomic populations. We believe that observation of population fluctuations can become a useful method for characterizing laser noise.

Michael W. Noel, W. M. Griffith, Thomas F. Gallagher