Intensity profile measurement of focussed CO2 laser beam using PMMA

Abstract

A method by which intensity profile and diameter of focussed CO2 laser beam are determined from the evaporated shape in PMMA (polymethyl methacrylate) has been developed. This method utilizes the fact that PMMA is sublimated by intenselaser beam with negligible thermal conduction and reflection losses. Two essential thermal constants of PMMA for estimating the intensity of the laser beam are determined; energy for evaporation H=3000 J/cm3, and threshold energy for evaporation G=6 J/cm2. It is shown that thus estimated profile is in good agreement with the profile determined by the probe techniques, and that the axi-symmetrical intensity distribution is determined from the deconvolution by Harker method. The optimum scanning speed, and tolerable scanning speed range in this technique are given as a function of power and spot size of laser beam. It is also shown that arbitrary intensity distributions can be determined by using PMMA.A method by which intensity profile and diameter of focussed CO2 laser beam are determined from the evaporated shape in PMMA (polymethyl methacrylate) has been developed. This method utilizes the fact that PMMA is sublimated by intenselaser beam with negligible thermal conduction and reflection losses. Two essential thermal constants of PMMA for estimating the intensity of the laser beam are determined; energy for evaporation H=3000 J/cm3, and threshold energy for evaporation G=6 J/cm2. It is shown that thus estimated profile is in good agreement with the profile determined by the probe techniques, and that the axi-symmetrical intensity distribution is determined from the deconvolution by Harker method. The optimum scanning speed, and tolerable scanning speed range in this technique are given as a function of power and spot size of laser beam. It is also shown that arbitrary intensity distributions can be determined by using PMMA.