Control of laser desorption using tunable single pulses and pulse pairs

We desorb ground state Br and spin-orbit excited Br* atoms from KBr single crystals using single pulses and sequential pulse pairs of tunable nanosecond laser radiation. Irradiation of cleaved KBr crystals near the bulk absorption threshold produces hyperthermal Br emission without a significant thermal component, and with little spin-orbit excited Br-* emission. The Br kinetic energy distribution may be controlled either by choice of photon energy or by excitation of transient defect centers created within the crystal. In this latter scheme, a first laser pulse generates transient centers within the bulk crystal and in the vicinity of the surface, and a second delayed laser pulse then excites the transient centers leading to atomic desorption. The Br-* to Br yield ratio is significantly enhanced using two-pulse excitation as compared to resonant single-pulse desorption. Single and multiple pulse excitation of KBr produces Br and Br-* in controllable quantities, velocities, and spin state distributions. (C) 2002 American Institute of Physics.