Laser ablation of polymers by ultra-short laser pulses (USLP): surface and bulk models

In the present communication we consider theoretically the effect of a single UV USLP and two successive UV USLPs on absorbing dielectrics near ablation threshold within the framework of a surface evaporation model and bulk photothermal models, which apply to polymer-like materials. In the case of pair-pulse ablation we investigate the dependence of the ablated depth on the delay time between USLPs (delay curve). We show that this curve is formed in two possible regimes. It is shown that these regimes influence the shape of the delay curve. We argue that these regimes are the same for the bulk model as well. It means that it is difficult to distinguish between the models investigating only this curve. We consider possible pump-probe experiment where USLP with the fluence somewhat higher than the ablation threshold is employed as a pump, whereas probe radiation allows to determine the delay time between pump pulse and the start of ablation. We show that combining the experimental data on determination of delay curve in pair- pulse experiment and the above pump-probe single ablation allows determination of an appropriate model. The results of theoretical modeling are compared with the existing data on time-resolved UV USLP laser ablation experiments.