Pulse strength and pulse duration effect on photoelectron polarisation in resonant two-photon ionisation

Abstract

Polarisation of photoelectrons produced from unpolarised alkali atoms is studied analytically for a wide range of the strengths and durations of the light pulse. In the particular case of long pulse durations, where the rate equation for the ionisation probability is approached, the photoelectron polarisation is shown to be a monotonically decreasing function of the pulse strength. In the case of weak pulses, usually dealt with by perturbation theory, the photoelectron polarisation is found to decrease continuously when the pulse duration is shortened. It is, however, found also that if neither the long pulse duration or the weak-field condition is fulfilled then an increase in pulse strength and a shortening of the pulse duration need not always affect the photoelectron polarisation destructively.