PNNL

Abstract

We have used the pump-probe technique to measure the photostimulated positive ion yield, as a function of time-delay between two sub-threshold femtosecond laser pulses. We find the ion yield, from UV femtosecond irratdiated MgO, depends critically on the laser pulse delay, delta-t, in two-pulse experiments. n single pulse experiments, excitation of MgO produces a variety of ions including Mg+, MgO+, and a significant yield of H+. In contrast, if the femtosecond laser pulse is split into two sub-threshold beams and then re-combined with a variable time delay, the ion yield may be drastically may be drastically altered depending on the delay between pulses. The Mg+ desorption yield displays three distinct liftimes and persists for laser delays of over 100 picosecond.