ABLATION OF POLYIMIDE (KAPTON(TM)) FILMS BY PULSED (NS) ULTRAVIOLET AND INFRARED (9.17-MU-M) LASERS - A COMPARATIVE-STUDY

Ablation of the surface of a polyimide (Kapton(TM)) film by single pulses of 248 nm or 308 nm radiation (approximately 20 ns) or 9.17 mum laser radiation (approximately 170 ns) was studied by photographing the emergence of the blast wave and the plume by a pulse (<1 ns; 596 nm) of visible laser light. The dynamics of the blast wave was similar in the ultraviolet and in the infrared but the composition of the plume was obviously different. A mass of opaque solid material was ejected for as long as 2.6 mus following the IR pulse in contrast to the minute amount of solids that are seen in the ablation by UV laser pulses of ns duration. UV laser pulses of 50-400 mus duration interact with polyimide surfaces in a manner that is similar to IR laser pulses of ns duration or longer. Chemical analysis of the ablation products that are obtained under various conditions of ablation when compared to the known modes of thermal degradation of polyimide show that the reaction is a thermal process when IR laser pulses or UV laser pulses of long (>10 mus) duration are employed. Ablation by ns UV laser pulses differs fundamentally in the chemistry of the products from all of the cases mentioned above.