Resonant Light Absorption in a Penning-Ionization Collision

The opening of a new channel of excitative Penning ionization by a collision-complex absorption of laser light has been observed in the system Ar*(${}_{}{}^3{}_{}{}^{}P$) + Ca. Two relatively broad resonances at 5958 and 5990 Å were found, corresponding to the production of ${\mathrm{Ca}}^{+}$($5p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$) and ${\mathrm{Ca}}^{+}$($5p{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$), respectively. The data indicate that the laser-assisted Penning-ionization cross section to these states exceeds that of the field-free ionization to ${\mathrm{Ca}}^{+}$($4p{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$).