Fundamental ablation of argon - flouride excimer laser on polymethyl methacrylate by interferomety technique

Abstract

A fundamental study is carried out to fabricate or in other words to ablate an optical material by using a single pulse of ultraviolet light. In this case, argon fluoride excimer laser has been used as the ultraviolet light source while polymethyl methacrylate (PMMA) sample is used as the optical material. The laser ablation was conducted in between 1 to 20 pulses as a fundamental ablation. The ablation effects on the PMMA sample were analysed by using interferometry method. Straight line and equidistance fringes pattern is an indicator for smooth and flat surface. The effect of ablation was quantified by measuring shifted distance, intensity changes, and spacing reduction of fringes. The initial fringes shifted were notified as ablation threshold. This occurred after 9 pulses of exposures with corresponding threshold fluence of 3.18 mJ/mm2. The fringes pattern becomes peculiar and difficult to trace at higher exposures. This contributed the increasing in shifted distance and fluctuating in the fringes intensity. High degree of surface roughness is indicated by the large fraction number of half wavelength and speckle existence. The resolidified of removal particles are possibly responsible to cause the refractive index of the tested region become fluctuated in the range of 1.43 to 1.49. By increasing number of laser pulses from 10 pulses to 20 pulses after ablation threshold, the ablation depth on the tested region was estimated and found that the depth varied in between 40 nm to 800 nm. The corresponding laser fluence had given were in between 3.6 mJ/mm2 to 7.3 mJ/mm2. Hence the fundamental study succeeds to ablate the PMMA material by using ultraviolet light of excimer laser