Observation of Pulsed Laser – Induced Melting of Solid Surfaces by Optical Spin Orientation

Abstract

ABSTRACTThe optically induced spin polarization P of the photoelectrons emitted from tin and germanium during ps and ns laser pulses is measured as a function of the pulse energy. P is defined by the lattice symmetry of the sample. It vanishes for amorphous or molten surfaces. The melting of the metal and the semiconductor is found to occur on a time scale which is short compared to the duration of a 70 ps laser pulse. The emission of positive ions starts at the laser intensity for which the drop of the polarization is observed. If Ge is heated with ns laser pulses a temperature dependent shift of the work function causes a decrease of the spin polarization for laser energies far below the energy necessary for melting. With ps laser pulses the polarization only vanishes for pulse energies exceeding Eion- The difference between the ps and ns measurements on Ge points to an unexpected dynamical behavior of the work function shift in semiconductors.