Direct measurement of reflectance from aluminum alloys during CO(2) laser welding

A simple method for measuring the reflected amount of a CO(2) laser beam from the surface of a welded aluminum alloy is described. This device can be used for cases in which an integrating sphere is impractical to use. A pyroelectric detector measures the amount of reflected laser radiation at prespecified locations that define a semisphere on top of the weld spot. The spatial distribution of a reflected laser beam is obtained. It is found that ~80% of the total incident power is reflected by the alloy until a welding keyhole is developed. However, once the keyhole is formed, the reflected amount is as low as 4-8%.