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Acta Optica Sinica

Effect of multiphoton process and spontaneous emission on laser induced autoionization

In F

Published Jan 1, 1987• 0 citations
OpenAlex

Abstract

The atoms at autoionization state can be excited to higher continuum state, as well as transit to bond states by spontaneous emission a photon in laser induced autoionization. The effect of these processes on the laser induced autoionization process has been investigated by means of using the reaction matrix. The effect of spontaneous emission process is small in general case, but its spectrum shows that the emission is contributed mainly from the spontaneous Raman scattering enhanced by the cutoioni-zation state, and the Dressed atom picture was shown clearly. The multiphoton process makes the photoelectron spectra and laser induced autoionization process very complicated. For example, the photoelectron spectra of one and two-photon process have multi-maxium structure.

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Acta Physica Sinica (Overseas Edition)•Aug 1, 1993•0 citations
The atoms at autoionization state can be excited to higher continuum state, as well as transit to bond states by spontaneous emission a photon in laser induced autoionization. The effect of these processes on the laser induced autoionization process has been investigated by means of using the reaction matrix. The effect of spontaneous emission process is small in general case, but its spectrum shows that the emission is contributed mainly from the spontaneous Raman scattering enhanced by the cutoioni-zation state, and the Dressed atom picture was shown clearly. The multiphoton process makes the photoelectron spectra and laser induced autoionization process very complicated. For example, the photoelectron spectra of one and two-photon process have multi-maxium structure.
Atoms in an autoionisation state can be excited to higher states in the continuum as well as performing spontaneous transitions to bound states by laser-induced autoionisation. Both effects are investigated by means of the reaction matrix. Results obtained by Armstrong et al (1978) using the same method are extended. The shape of the photoelectron spectrum is different from that of the photon spectrum emitted from the autoionisation state but is similar to that of the photon spectrum emitted from the same bound state which is excited to the ionisation states in the former case. It is predicted that the shape of the fluorescence yield with the pump laser detuning is Lorentzian. The multiphoton process contributes to the photoelectron spectrum in a complicated way.
Using the R -matrix Floquet theory we have carried out non-perturbative, ab initio one- and two-colour calculations of the multiphoton ionization of magnesium with the laser frequencies chosen such that the initial state of the atom is resonantly coupled with autoionizing resonances of the atom. Good agreement is obtained with previous calculations in the low-intensity regimes. The single-photon ionization from the excited state of magnesium has been studied in the vicinity of the autoionizing resonance at non-perturbative laser intensities. Laser-induced degenerate states (LIDS) are observed for modest laser intensities. By adding a second laser which resonantly couples the and autoionizing levels, we show that, due to the small width of the state, LIDS occur between this state and the state at intensities of the first laser below . We next investigate the case in which the first laser induces a resonant two-photon coupling between the ground state and the autoionizing state, while the second laser again resonantly couples the respective and autoionizing states. At weak intensities, our calculations compare favourably with recent experimental data and calculations. We show that when the intensity of the first laser is increased, the effect of an additional autoionizing state, the state, becomes significant. This state is coupled to the autoionizing level by one photon, inducing a triply resonant processes. We show that LIDS occur among the three autoionizing levels and we discuss their effect on the decay rate of the ground state. We consider dressed two- and three-level atoms which can be used to model the results of our calculations.
We present the experimental and theoretical investigation of the effects of the strong electromagnetic coupling of two autoionizing states (AIS's) on the photoionization properties of an atomic system. These effects are observed by probing the ladder system from the ground state of the atom through a weak two-photon transition to the region of the lower AIS. The experimental observation of the modification of the total ionization and partial photoelectron spectra at different wavelengths of the coupling and probe lasers are accurately reproduced by a theoretical analysis which uses a density-matrix approach. Both theory and experiment indicate a strong inhibition of the ionization of the system in the case when both lasers are resonant with the two atomic transitions, while displaying a rapidly varying asymmetry induced as the detuning between the two states and the fields increases. In the extreme case of a large detuning, two separate structures appear as distinct total ionization and photoelectron peaks. The above findings combined with the full theoretical treatment indicate that the phenomena observed are an experimental demonstration of ac Stark splitting between two AIS's. \textcopyright{} 1996 The American Physical Society.
We have studied the effect of above-threshold transitions on the (1+1)-photon resonance-enhanced ionization and autoionization processes. We have shown that the effect of the photoionization decay of the autoionizing (AI) state to the higher continuum becomes dominant when the photoionization width of the AI state is comparable to or larger than the autoionization width to within an order of magnitude, i.e., for the intermediate range of laser intensity. The continuum-continuum coupling and the higher-order transitions become effective only for much higher values of the above-threshold transition strengths, i.e., for much higher values of the laser intensity. \textcopyright{} 1996 The American Physical Society.