The morphology of structural changes in KTP crystal induced by single femtosecond laser pulse has been investigated by means of CCD camera, scanning electron microscopy (SEM) and atom force microscopy (AFM). The structurally changed region is depressed at energies close to the threshold for producing a structural change and melting ablation morphologies are observed as pulse energy is increased. Furthermore, periodic nanostructures are formed around the edge of the laser-induced spots. (c) 2006 Elsevier B.V. All rights reserved.