Review Of Continuous Wave CO2 Laser Beam Measurement Techniques, And The Development Of A High Intensity Beam Scanner

TWI Industrial Member Report Summary 165/1981

By R C Crafer and P J Oakley

Background

Methods that are used to measure the three parameters that characterise the 10.6 µm wavelength beam of a continuous wave (cw) carbon dioxide laser are described. Beam power is measured by calorimetric techniques, using either the complete beam, or sampling a known fraction of the beam. Beam diameter and intensity distribution can be measured by heating or charring materials, and also by vaporising acrylic. However, the amount of information that can be deduced from such techniques is limited. The more sophisticated techniques that have been used to characterise high power CO₂ laser beams are outlined. Particular details are given of a Welding Institute developed high intensity beam scanner. using a photon drag detector. Its principle of operation and construction are described, and results given and interpreted for 2 and 5kW fast axial flow CO₂ lasers.