CHEMICAL-TRANSFORMATIONS OF THE POLYIMIDE KAPTON BROUGHT ABOUT BY ULTRAVIOLET-LASER RADIATION

By the use of ultraviolet laser pulses of microsecond and millisecond duration it is shown that the chemistry of the transformations of Kapt on by UV laser radiation is strongly dependent on the intensity (power /unit area) of the laser beam. With these long pulses, the polymer was not ablated. The decomposition resulted in 51% of the polymer weight being converted to gaseous products consisting mostly of CO (67%), HCN (15%), C2H2 (12%), and some (<5%) CO2. The major solid product that r emained was ''glassy'' carbon which was identified from its Raman spec trum. This material can be viewed as the product of the secondary addi tion reactions of the residue that is left after the loss of the gaseo us products listed above. With 20 ms pulses, the evolution of the gase ous products increased linearly with intensity and the product composi tion was constant within the experimental uncertainty over a 12-fold r ange of intensity up to 50 kW/cm(2) (=1 kJ/cm(2)). These results show that pulses of duration much greater than ns do not lead to ablation e ven at fluences that are 10(4) greater than the threshold for ablation using nanosecond pulses. It is therefore more appropriate to view the ablation of this polymer by UV laser pulses of nanosecond duration as being due to the scaling of an intensity threshold rather than a flue nce threshold as has become the practice. (C) 1995 American institute of Physics.