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 are examined as a function of successive laser pulses in UV ablation (λ=248 nm). The dopants include the strongly bound to the matrix C10H22 and the weakly bound (CH3)2O. For C10H22, the results are fully consistent with the volume expansion character of ablation. In contrast, for (CH3)2O, a high contribution through diffusion from underlying (i.e., nonejected) layers is demonstrated. This high diffusivity is consistent with melting of these layers during irradiation. Consequently, overheating of the upper/ejected layers well above the melting point is strongly suggested, in very good agreement with the `phase explosionʹ model for ablation.