UV LASER ABLATION OF MOLECULAR CRYOGENIC FILMS

In the irradiation of condensed phases at high laser irradiances, the ejection/removal of a high quantity of material is observed, and this is usually denoted by the term laser pulsed ablation (or explosive desorption). This phenomenon has found extensive and very important applications, but its mechanistic understanding is very poor. The present work addresses two questions: Can a physically significant criterion be established for defining the phenomenon? How physical and chemical processes in this regime differ from those at low light irradiances where conventional photophysics/chemistry holds? To address these questions, model systems composed of simple organic compounds frozen at low tempeartures are studied. Time-of-flight mass spectrometry is employed to probe ejection efficiencies as a function of laser parameters and optical/imaging techniques are employed for probing morphological/structural changes induced in the film. Through the comparative examination of nonabsorbing dopants of different binding energies to the matrix (C6H5CH3), it is demonstrated that in the UV irradiation