Experimental Evidence for Selection Rules in Multiphoton Double Ionization of Helium

TL;DR

This paper provides experimental evidence that quantum mechanical selection rules, specifically parity considerations, govern the phase space modulations observed in correlated electron emission during strong field double ionization of helium.

Contribution

It experimentally confirms the theoretical prediction that selection rules based on photon number parity influence electron emission patterns in helium ionization.

Findings

Phase space modulations occur only for an odd number of absorbed photons.

Modulations are linked to the parity of the continuum wave function.

Experimental results match quantum mechanical predictions.

Abstract

We report on the observation of phase space modulations in the correlated electron emission after strong field double ionization of helium using laser pulses with a wavelength of 394~nm and an intensity of $3\cdot10^{14}$W/cm$^2$. Those modulations are identified as direct results of quantum mechanical selection rules predicted by many theoretical calculations. They only occur for an odd number of absorbed photons. By that we attribute this effect to the parity of the continuum wave function.