Laser-stimulated atomic migration

Abstract

The effects of stimulated Raman scattering (SRS) and of infrared (IR) absorption on the scattering at defects leading to atomic migration in solids is evaluated in detail for certain systems. \DeltaE/kT \approx \sum u_{ic}^{2}/\langleu_{i}u_{i}\rangle , where \DeltaE is the activation energy, u ic is the many-body critical displacement in a migration event, and \langleu_{i}u_{i}\rangle is the equal-time correlation function including anharmonic terms. Using the equal-time correlation for the defect lattice in the harmonic approximation, we get \DeltaE/kT_{eff} \propto 1/\sum h[2(n_{s} + n_{e}) + 1] where T eff includes both n e and n s the externally and thermally excited phonon numbers, respectively. The phonon rate density required for an observable effect of SRS or IR absorption on diffusion in solids is n_{e}^{(c)}c_{s}/V \approx 10^{26} - 10^{27} phonons/s.cm2, where n_{e}^{(c)} is a critical number of high wave-vector laser-stimulated phonons, c s , is the sound velocity, and V, the volume per atom. In KCI at 110 K, theory shows that n_{e} = 0.2 can produce a factor of 10 effect on the reorientation of Na:F A centers. Anharmonic effects on \langleu_{i}u_{i}\rangle were calculated and numerical estimates indicate that they would be experimentally observable for large n e . It is found that some of the effects reported here probably contribute, in part, to the permanent damage tracks caused by high-power laser beams in solids and provide an internal source for the initiation of microcracks. In addition, the direction of the stimulated phonon wave vector is shown to produce a directional effect in the control of atomic migration.