Multiphoton Ionization and Third Harmonic Generation in Alkali Atoms

R. N. Compton, Michael A. Duncan

Published Nov 27, 2024• 0 citations

Abstract

Abstract Experiments involving resonantly enhanced multiphoton ionization (REMPI) of alkali atoms contained in a heat pipe are discussed with reference to the quantum defect theory modification of the hydrogen atom energy levels. Quantum defects for the ns and nd levels are extracted from the data. This experiment is an excellent introduction to atomic spectroscopy and the selection rules involved. Ionization potentials are extracted from the Rydberg spectra. In the second part of this chapter a Raman shifter is employed to produce IR photons for multiphoton excitation of the low-lying p states of cesium. Three-photon excitation also produces third harmonic generation. The use of heat pipes for the production of alkali metal atom vapor is discussed as well as the use of a simple pick-up wire for ion detection.

DOI: 10.1093/oso/9780198900825.003.0016

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Multiphoton Ionization and Third Harmonic Generation in Alkali Atoms

R. N. Compton, Michael A. Duncan

Published Nov 27, 2024• 0 citations

Publisher

Abstract

DOI: 10.1093/oso/9780198900825.003.0016

Related papers

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Physical Review AJun 1, 198821 citations

{10}^{8}

{\mathrm{cm}}^{2}

) is determined by the intensity-dependent level width (

6f

configuration) as well as the interference of the fine-structure states, and that the rates for hydrogen, in a much more intense beam (of order

{10}^{12}

{\mathrm{cm}}^{2}

) are determined by both the intensity-dependent widths and shifts a

\stackrel{\mathrm{`}}{\mathrm{s}}

well as the wave-function renormalization constants. The agreement of these two examples of calculations with the experiments done recently is satisfactory. For third-harmonic production the role of two-photon resonance is emphasized, and the dependence of the generated third-harmonic intensity on the intensity and frequency of the fundamental is discussed. Near resonance, the ratio of third-harmonic intensity to fundamental intensity saturates.

In this paper we analyze two-photon-resonant three-photon ionization of atomic oxygen via the 2

{\mathit{p}}^{3}

{(}^{4}

S\ifmmode^\circ\else\textdegree\fi{})

{\mathit{np}}^{3}

{\mathit{P}}_{0}

,1,2, and the 2

{\mathit{p}}^{3}

{(}^{4}

S\ifmmode^\circ\else\textdegree\fi{})nf

^{3}

{\mathit{F}}_{2}

,3,4 states. The various atomic parameters required for calculating the resonant enhanced multiphoton ionization (REMPI) probabilities are obtained using quantum-defect theory. The infinite sums over nonresonant states are truncated at a finite number of terms. Our calculated two-photon excitation cross sections agree well with the results of other recent calculations and of experimental measurements. The photoionization cross section is calculated for various electron kinetic energies. The REMPI dynamics is analyzed by solving the density-matrix equations. This framework consistently takes into account the effects of saturation and ac Stark shifts. REMPI probability is seen to be quite sensitive to the initial detuning, the intensity, and the particular resonant state accessed. The photoionization cross sections also imply that due to the rapid falloff of the cross section, two-color REMPI schemes with a lower-frequency ionizing photon would increase the effective REMPI probability.