Resonant multiphoton ionization by finite-bandwidth chaotic fields

Resonant multiphoton ionization by finite bandwidth multimode radiation is investigated without the restriction of either a "long" or a "short" correlation time of the field. By approximating the multimode radiation by a stochastic model of a chaotic field, the stochastic atomic-density-matrix equation is reduced to a tractable infinite set of differential equations. For a given bandwidth this set can be suitably truncated and numerically integrated. For large-bandwidth fields it turns out that these truncated equations constitute a systematic improvement of the method usually employed of decorrelating the atom-field variables. For zero-bandwidth fields the well-known result is recovered in that the statistical averaging of the ionization probability reduces to an average with respect to the Glauber $P$-distribution function of the chaotic field. Detailed results of numerical calculations for two-photon ionization are presented which reveal a number of new interesting features.