Gc. Dcouto et Sv. Babu, HEAT-TRANSFER AND MATERIAL REMOVAL IN PULSED EXCIMER-LASER-INDUCED ABLATION - PULSEWIDTH DEPENDENCE, Journal of applied physics, 76(5), 1994, pp. 3052-3058
The pulsewidth-dependent ablation of polyimide, poly(methylmethacrylat
e), poly (etheretherketone), poly(ethylene terepthalate), and poly(eth
ersulphone) exposed to 248 and 308 nm, nanosecond UV laser pulses was
modeled assuming one-dimensional heat transfer and a published model [
G. H. Pettit and R. Sauerbrey, Appl. Phys. A 56, 51 (1993)] for photon
absorption. The polymers were assumed to degrade/ablate after reachin
g a threshold temperature determined either from published temperature
calculations of the ablating surface or the ceiling temperature. Sinc
e heat transfer calculations suggest that this temperature is reached
before the end of the laser pulse, it was assumed that the degraded/ab
lated material continues to attenuate the incoming laser energy for th
e remaining duration of the laser pulse. Since the fluence-dependent a
bsorption coefficient of this degraded material is unknown, it was obt
ained by fitting the experimental pulsewidth dependent ablation rate d
ata of Schmidt, Ihlemann, and Wolff-Rottke (unpublished). The resultin
g values are consistent with mass spectrometric analysis of the ablati
on products and with the absence or occurrence of incubation. The thre
shold fluences and ablation rates predicted by this model are in good
agreement with reported literature values; however, the use of a well-
defined threshold temperature in the model leads to a different limiti
ng etch rate dependence on the fluence at the threshold.