Field-intensity-dependence of the assistedHe/emph>(21S,23S) +He(11S) ionizing collision

We report complementary measurements of the ${\mathrm{He}}^{+}$ signal from the laser-assisted collision ${\mathrm{He}}^{\mathrm{*}}$($2^1$S,$2^3$S)+He(1 ${}_{}{}^1{}_{}{}^{})+$ħω → ${\mathrm{He}}^{+}$ ${(1\mathrm{}}^2$S)+He${(1\mathrm{}}^1$S)+e ${}_{}{}^{\mathrm{-}}{}_{}{}^{}$. A new higher-performance laser has been used in order to improve signal-counting statistics and to determine the variation in the signal as a function of laser intensity. As expected, a linear variation is obtained over a wide range of intensities. This is an important characteristic of laser-assisted processes, which reinforces the proofs already reported in a previous work [P. Pradel et al., Phys. Rev. Lett. 54, 2600 (1985)].