Time-resolved UV absorption of polyimide |
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Authors: | J K Frisoli Y Hefetz T F Deutsch |
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Institution: | (1) Department of Dermatology, Harvard Medical School, Wellman Laboratories of Photomedicine, Massachusetts General Hospital, 02114 Boston, MA, USA |
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Abstract: | The 355-nm transient absorption of polyimide thin films has been measured following excitation withsubablative, 24-ps long, 355-nm laser pulses. The 355-nm absorption increases by 25% following 355-nm, 20 mJ/cm2 excitation and recovers with a fast time constant 34 ps, and a slow time constant which is much longer than 6 ns. The data are fitted by a three-level rate equation model incorporating the temperature dependence of the ground state absorption coefficient. The fast component is attributed to the decay ofS
1 and the slow component results from increased ground state absorption caused by a laser-induced temperature rise. The nonlinear intensity dependence is attributed to excited state (S
1) absorption. These results indicate the importance of considering the dynamic absorption in modelling ablation. |
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Keywords: | 78 47 +p |
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