Title: Experimental Evidence for Selection Rules in Multiphoton Double Ionization of Helium,
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.