Pulse dependence of ejection efficiencies in the UV ablation of bi-component van der Waals solids

The ejection intensities of dopants incorporated within a C6H5CH3 matrix ar e examined as a function of successive laser pulses in UV ablation (lambda = 248 mn). The dopants include the strongly bound to the matrix C10H22 and the weakly bound (CH3)(2)O. For C10H22, the results are My consistent with the volume expansion character of ablation. In contrast, for (CH3)(2)O, a h igh contribution through diffusion from underlying (i.e., nonejected) layer s is demonstrated. This high diffusivity is consistent with melting of thes e layers during irradiation. Consequently, overheating of the upper/ejected layers well above the melting point is strongly suggested, in very good ag reement with the 'phase explosion' model for ablation. (C) 2001 Elsevier Sc ience B.V. All rights reserved.