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Physical Review A

Interference effects in the two-photon ionization of metastable helium

Ravi Sharma, K. C. Mathur

Published Nov 1, 1979• 5 citations
Publisher

Abstract

Multipole interference effects are predicted in the generalized cross sections, and in the ratio $\frac{{\stackrel{^}{\ensuremath{\sigma}}}_{C}}{{\stackrel{^}{\ensuremath{\sigma}}}_{L}}$ of the cross sections for circularly and linearly polarized laser light for the case of the two-photon ionization of the $n=2$ singlet metastable helium atoms in the wavelength range 5036-5050 \AA{}.

DOI
10.1103/physreva.20.2241

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Multipole interference effects are predicted in the generalized cross sections, and in the ratio \frac{{\stackrel{^}{\ensuremath{\sigma}}}_{C}}{{\stackrel{^}{\ensuremath{\sigma}}}_{L}} of the cross sections for circularly and linearly polarized laser light for the case of the two-photon ionization of the n=2n=2n=2 singlet metastable helium atoms in the wavelength range 5036-5050 \AA{}.
The two-photon ionization of the He atom in the 21S2^{1}S21S state is studied in the electric dipole plus quadrupole approximation. A quadrupole resonance peak in the generalized cross section is obtained at 5043.5 \AA{}A. It is shown that for incident photons having wavelengths between 5042 and 5045 \AA{}A, the quadrupole term gives a significant contribution to the total generalized cross section.
The polarization dependency of relative cross-sections of the two-photon REMPI dipole transition (2$\sp1$S-3$\sp1$P) and quadrupole transition (2$\sp1$S-3$\sp1$D) is studied experimentally. Strict attention is paid to the measurement statistics, particularly to those associated with the ionizing laser beam. The cross section profiles are fitted to Voight functions that are generated from the measurement of experimental parameters. Ratios of the circular to linear polarization ion yields are also reported. These ratios are compared to theoretical predictions.