We recently demonstrated that sub-band gap photoexcitation of KBr near 6.4 eV leads to desorption of hyper-thermal neutral bromine atoms without a significant thermal velocity component. In contrast, a considerable thermal velocity component is observed at higher excitation energies and is attributed to formation and subsequent diffusion of transient centers from within the bulk crystal to the surface. Excitation with a nanosecond laser at 3.5 eV also produces neutral bromine emission with a seemingly thermal velocity profile, but a near three-photon power dependence. Furthermore, the relative Br* yield is greatly enhanced. We propose an explanation for these results based on formation and secondary excitation of transient defect centers in KBr by individual nanosecond pulses. Photodecomposition of newly formed transient centers leads to emission of Br and Br* in a "near thermal" velocity distribution. These results are likely general for alkali halides and are consistent with a recently described theoretical model. (C) 2002 Elsevier Science B.V. All rights reserved.