Multiphoton Ionization of Rare Gases at Very High Laser Intensity (1015W/cm2) by a 30-psec Laser Pulse at 1.06 μm

Abstract

A bandwidth-limited 30-psec laser pulse at 1.06 μm is used to investigate multiphoton ionization of noble gases at very high laser intensity (${10}^{15}$ W/${\mathrm{cm}}^2$). For helium atoms interacting with a laser intensity of 1. 1×${10}^{15}$ W/${\mathrm{cm}}^2$, no departure from a pure 22-photon ionization process is observed, in contradiction with the few theoretical calculations which predict that a tunneling effect should appear in this laser-intensity range.