Search results for "Above threshold ionization"
showing 6 items of 6 documents
Ionization of atomic hydrogen with up to four excess photons by circularly and linearly polarized light
2012
The above threshold ionization (ATI) is investigated for H in ns states. The total generalized cross sections are calculated for up to 4 excess photons using perturbation theory and modified Coulomb Green's function Sturmian expansion.
Strong-field high-frequency approximation to the multiphoton ionization of hydrogen
1990
The strong-field multiphoton ionization of atoms is considered and a theoretical approach dealing nonperturbatively with the radiation field formulated. The general computational scheme is the conventional perturbation theory, but the intermediate states are dressed by the field. We present in detail a method to dress the continuum states and to study the dipole transitions within the continuum. In the high-frequency domain, the proposed procedure rapidly converges over a wide range of field intensity and offers an interesting framework for calculating ionization rates for arbitrary numbers of absorbed (above-threshold) photons and field polarization.
From Above Threshold Ionization to Statistical Electron Emission: The Laser Pulse-Duration Dependence ofC60Photoelectron Spectra
2000
The photoelectron spectra of C60 ionized using a 790 nm laser with pulse durations varying from 25 fs to 5 ps have been determined. For 25 fs pulses, in the absence of fragmentation, the ionization mechanism is direct multiphoton ionization with clear observation of above threshold ionization. As the pulse duration is increased, this becomes dominated by a statistical ionization due to equilibration among the electronic degrees of freedom. For pulse durations on the order of a ps coupling to the vibrational degrees of freedom occurs and the well-known phenomenon of delayed (ms) ionization is observed.
The general expression for the transition amplitude of two-photon ionization of atomic hydrogen
2003
Two-photon ionization of atomic hydrogen with an excess photon is revisited. The non-relativistic dipole approximation and Coulomb Green function (CGF) formalism are applied. Using the CGF Sturmian expansion straightforwardly, one gets the radial transition amplitude in the form of an infinite sum over Gauss hypergeometric functions which are polynomials. It is convergent if all intermediate states are in the discrete spectrum. In the case of two-photon ionization with an excess photon, when photoionization is also possible, intermediate states are in the continuum. We performed the explicit summation over intermediate states and got a simple general expression for the radial transition amp…
Above threshold ionization of atomic hydrogen inns states with up to four excess photons
2010
In a high-intensity laser field an atom can absorb more photons than the minimum necessary for ionization. It is known as above threshold ionization (ATI). Theoretically it is the most difficult case to handle as we have to consider transitions in continuum. To study ATI we use the perturbation theory and Green's function formalism. We have derived the modified two-term Coulomb Green's function (CGF) Sturmian expansion. In each term explicit summation over all intermediate states is carried out. The transition amplitude may be obtained in a closed form. The generalized cross sections are evaluated for the photoionization of atomic hydrogen in ns states with up to four excess photons. Calcul…
Strong chiral dichroism and enantiopurification in above-threshold ionization with locally chiral light
2021
We derive here a highly selective photoelectron-based chirality-sensing technique that utilizes “locally chiral” laser pulses. We show that this approach results in strong chiral discrimination, where the standard forwards/backwards asymmetry of photoelectron circular dichroism (PECD) is lifted. The resulting dichroism is larger and more robust than conventional PECD (especially in the high-energy part of the spectrum), is found in all hemispheres, and is not symmetric or antisymmetric with respect to any symmetry operator. Remarkably, chiral dichroism of up to 10% survives in the angularly integrated above-threshold ionization (ATI) spectra, and chiral dichroism of up to 5% survives in the…