Laser pulse duration effects in Xe2+ ions induced by multiphoton absorption at 0.53 μm

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Abstract
Xe2+ ions can easily be formed by multiphoton absorption in Xe atoms at 0.53 μm. At low laser intensities, a laser-Xe atom interaction takes place which generates Xe2+ ions through a 15-photon absorption from Xe atoms. At higher intensities, a laser-Xe+ ion interaction takes place, generating Xe2+ ions through a 10-photon absorption from the Xe+ ion in its ground state. The former process is very sensitive to the laser pulse duration in the 5-200 ps range used here. As an example, the number of Xe2+ ions is increased by a factor of 30 when the pulse duration is decreased from 30 to 5 ps. The laser intensity at which this occurs is approximately 1012 W . cm- 2. A kinetic model is developed which is based on the rate equations describing the evolution of populations of Xe atoms, Xe + and Xe2+ ions. The result is that the ratio of the number of Xe2+ to Xe+ ions varies with the pulse duration τ as τ-3/2