Visualization of molten pools and invisible laser beam profiles using an ultraviolet CCD camera

Abstract

A visualization technique using an ultraviolet CCD camera has been successfully applied to the non-contact monitoring of molten pools produced in material processing by high power CO_2 lasers. This technique is based on the principle that the temperature sensitivity of UV radiation emitted from molten pools is much higher than visible or infrared region. Additionally, the target area directly irradiated by a focused laser beam could be largely dominated by UV radiation because of its highly energetic condition. In this experiment, molten pools produced by a 100-W CO_2 laser were observed as 250-nm UV images by means of an UV-CCD imaging system. It has been attractively demonstrated that the developed technique could offer not only more realistic pictures of actual laser focused area without the secondary effects due to heat conduction around them, but also the intensity profiles of the incoming, invisible laser beam. The 3-D representation of laser beam intensity profile has been reconstructed through the contour maps of UV images captured at a laser irradiated target region, with showing a very small deviation of 5% from the ideal Gaussian distribution. The obtained results imply that this visualization method could be an alternative beam profiling technique to conventional acrylic burning method which has much larger deviations in beam profiling.