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Physical Review A

Near-threshold photoionization and photodetachment by an exponentially decaying pulse

Andrzej Raczyński, Jarosław Zaremba

Published Nov 1, 1988• 9 citations
Publisher

Abstract

The photoelectron spectra in photodetachment of a negative ion and in atomic photoionization by an exponentially decaying laser pulse are analyzed. The possibility of a multipeak structure for these spectra in a highly nonperturbative regime is predicted. Various properties of the spectra are also discussed.
DOI
10.1103/physreva.38.5115

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Photodetachment of an electron from a negative ion in the near-threshold region. II. Pulses of radiation with smooth time envelopes

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Near-threshold photoionization by pulses with modulated frequency

Andrzej Raczyński, Jarosław Zaremba

Model photoionization by a pulse with a modulated frequency is discussed. An approximation generalizing that of Weisskopf-Wigner is proposed, with a pole moving in the rhythm of the modulation. A model taking into account the ionization threshold is adopted, and relatively simple formulas for the nondecay probability and the photoelectron spectrum are obtained. A nonexponential character of the decay curves is demonstrated together with a raising and narrowing of the peaks in the photoelectron spectra.

Physical Review A•Mar 1, 1998•1 citation
Near-threshold single-photon photodetachment processes are considered for simple model systems representing negative ions exposed to monochromatic radiation. The model systems considered feature an initial discrete state, the photoelectron continuum, and in some cases an excited or autodetaching discrete state. Population trapping through the formation of a bound dressed state and the photoelectron spectra are examined. Two photoelectron spectra are defined : a primary spectrum which results from decay while the laser interaction is on and a secondary spectrum which results from the destabilization of the bound dressed state if the interaction is turned off again. Careful attention is given to the passage of the poles of the Green's operator through the low-energy boundary of a continuum, and it is concluded that such poles move nonmonotonically through the boundary of an s-wave continuum, but monotonically through the boundary of a p-wave or higher-l-wave continuum. Two example systems, one featuring a single discrete state and an s-wave continuum and one featuring two discrete states and a p-wave continuum, are considered in detail.
Near threshold photodetachment of electrons from negative ions is investigated theoretically. Various profiles of the laser pulse time envelope f(t) are considered. The Stark shift ( delta E 0 ) max of the ground level E 0 is assumed to be large mod ( delta E 0 ) max mod tau >>1, where tau is the pulse duration. The saturation regime found earlier is shown to be realisable rigorously only in the case of the exponential envelope f 0 (t)=exp(- mod t mod / tau ). For any other f(t) deviations from the saturation are shown to be larger the more significantly f(t) deviates from f 0 (t). In the case of the Gaussian curve f(t) the photodetachment probability w depends only slowly (logarithmically) on the peak field strength E 0 . The function w(E 0 ) is shown to depend not only of f(t) but also on the detuning from the threshold Delta . For some model functions f(t) the dependence w(E 0 ) is found analytically for all Delta , mod Delta mod <or approximately= mod ( delta E 0 ) max mod . For large positive Delta the photodetachment probability is found for any envelope f(t).
For pt.I see ibid., vol.16, p.3641 (1983). The photodetachment of an electron from a negative ion is investigated in the near-threshold region. Pulses of electromagnetic radiation with a smooth envelope are considered. The strong Stark shift of the ground level is shown to influence essentially the regimes of the field-induced decay. The probability of photodetachment is found analytically for the envelope described by the curve f(t)=exp(- mod t mod / tau ). The cases with various relations between the Stark shift, pulse duration tau and detuning from the threshold are analysed. The probability w is found both for a positive and a negative polarisability alpha ( omega ) of the ground state. A partial stabilisation (when alpha ( omega )>0) and destabilisation (when alpha ( omega )<0) of the negative ion due to the strong laser field are discussed.
Model photoionization by a pulse with a modulated frequency is discussed. An approximation generalizing that of Weisskopf-Wigner is proposed, with a pole moving in the rhythm of the modulation. A model taking into account the ionization threshold is adopted, and relatively simple formulas for the nondecay probability and the photoelectron spectrum are obtained. A nonexponential character of the decay curves is demonstrated together with a raising and narrowing of the peaks in the photoelectron spectra.