Laser induced intrinsic defects: Subpicosecond study of trapping kinetics

• Published in: Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms Beam interactions with materials and atoms, 1998-05, Vol.141 (1), p.66-72
• Main Authors: Guizard, Stéphane, Itoh, Chihiro, Martin, Philippe, Meynadier, Pierre, D'Oliveira, Pascal, Perdrix, Michel, Petite, Guillaume
• Format: Article
• Language: English
• Subjects: Kbr; Laser irradiation; NaCl; Point defects
• ISSN: 0168-583X; 1872-9584
• DOI: 10.1016/S0168-583X(98)00189-X

We use a time resolved interferometric method to study the kinetics of carriers trapping and defects formation following electronic excitation by high intensity ultrashort laser pulses in alkali halides. A systematic study of initial excitation density dependence of trapping kinetics, as well as the comparison of pure and doped samples, allows to investigate in detail the mechanism of energy relaxation and carriers localization accompanying the lattice rearrangement. The experimental results concern samples of pure and NO − 2 doped KBr, and of pure NaCl. We observe faster trapping in KBrNO − 2 than in pure KBr. In NaCl, the trapping rate increases with excitation density. These results show that in both materials the hole trapping is the primary process towards radiation induced defects. Furthermore, in KBr our results give strong evidence for the existence of an intermediate state with a short lifetime in the relaxation pathway between the initial electron–hole pairs and the final F–H pairs. A simple model describing the modification of the refractive index and rate equations governing free and trapped electron and holes populations are used to quantitatively interpret the experimental results.