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Journal of Physics B Atomic and Molecular Physics

Two-photon ionisation of atomic hydrogen simultaneously with one-photon ionisation

Erna Karule

Published Feb 14, 1978• 73 citations
Publisher

Abstract

Two-photon ionisation of atomic hydrogen in the ground state with linearly and circularly polarised light is considered. In the region above the one-photon ionisation threshold expressions for the two-photon ionisation transition matrix elements are obtained using the non-relativistic dipole approximation. The two-photon ionisation rate is calculated above and below the one-photon ionisation threshold. Above threshold the total cross section for two-photon ionisation has no resonances and diminishes more rapidly than the photoionisation cross section as the wavelength decreases.

DOI
10.1088/0022-3700/11/3/015

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For pt.I see ibid., vol.19, p.79 (1986). The authors study the two-photon ionisation of unpolarised target atoms of caesium in their ground state or in one of the two first excited states 6P 1/2 or 6P 3/2 in the non-resonant region. Circularly, linearly and unpolarised light are considered. For each case they give a systematic analysis of generalised transition probabilities, angular distributions and polarisation phenomena. In particular, it is shown that polarised electrons can be obtained even with linearly or unpolarised light.

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Multiphoton Ionization of Atomic Hydrogen in the Ground State

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The general theory of multiphoton ionization of hydrogen atoms by simultaneous absorption of several photons is discussed. In the nonrelativistic dipole approximation, the calculations lead to a recursion relationship concerning angular functions and involve radial matrix elements containing many summations over intermediate states. A general method for exactly evaluating several sums is described in detail and applied to the photo-ionization of atomic hydrogen in the ground state. Numerical results are presented as dispersion curves of the transition rate $\frac{{\ensuremath{\sigma}}_{n}}{{I}^{N\ensuremath{-}1}}$ for a range of wavelengths from 1000 up to 7200 \AA{}.

Physical Review•Aug 5, 1968•133 citations
Two-photon ionisation of atomic hydrogen in the ground state with linearly and circularly polarised light is considered. In the region above the one-photon ionisation threshold expressions for the two-photon ionisation transition matrix elements are obtained using the non-relativistic dipole approximation. The two-photon ionisation rate is calculated above and below the one-photon ionisation threshold. Above threshold the total cross section for two-photon ionisation has no resonances and diminishes more rapidly than the photoionisation cross section as the wavelength decreases.
Two-photon ionisation of atomic hydrogen is considered in the non-relativistic dipole approximation at the photoelectric threshold and above it. In this region are obtained convergent analytical expressions for the radial transitions matrix elements, necessary for the calculation of ionisation rates. Partial and total cross sections per unit intensity are calculated for two-photon ionisation of atomic hydrogen in excited states with 2<or=n<or=9 by linearly and circularly polarised light at the photoelectric threshold and above it. At the photoelectric threshold calculations are also carried out for the two-photon ionisation of atomic hydrogen in the ground state.
A density-matrix formulation is given of two-photon ionisation of alkali atoms, for two incoming light pulses of arbitrary direction, polarisation, pulse duration and time difference. The frequency of one of the pulses coincides with a resonant transition. The emphasis is on separating out angular momentum factors from the basic physics contained in the radial matrix elements of the atomic electric dipole. The bandwidth of the exciting light is assumed large compared to natural and induced linewidths. The polarisation of the photoelectron is calculated with or without saturation of the excitation for various values of the nuclear spin.
For pt.I see ibid., vol.19, p.79 (1986). The authors study the two-photon ionisation of unpolarised target atoms of caesium in their ground state or in one of the two first excited states 6P 1/2 or 6P 3/2 in the non-resonant region. Circularly, linearly and unpolarised light are considered. For each case they give a systematic analysis of generalised transition probabilities, angular distributions and polarisation phenomena. In particular, it is shown that polarised electrons can be obtained even with linearly or unpolarised light.
The general theory of multiphoton ionization of hydrogen atoms by simultaneous absorption of several photons is discussed. In the nonrelativistic dipole approximation, the calculations lead to a recursion relationship concerning angular functions and involve radial matrix elements containing many summations over intermediate states. A general method for exactly evaluating several sums is described in detail and applied to the photo-ionization of atomic hydrogen in the ground state. Numerical results are presented as dispersion curves of the transition rate $\frac{{\ensuremath{\sigma}}_{n}}{{I}^{N\ensuremath{-}1}}$ for a range of wavelengths from 1000 up to 7200 \AA{}.