Beam characterization for Nd:YAG spot welding lasers

The application of Kapton film and the Prometec Laserscope for measuring spot welding laser spotsize has been investigated. The Laserscope measurements enabled a direct comparison with Kapton film results to be made. To synchronize hollow needle rotation of the Laserscope with the laser pulsation required the construction of a timing circuit. Four thicknesses of Kapton film (25, 50, 75, and 125 µm) were tested. For both the Kapton and Laserscope tests, multiple measurements about the focal plane were made at different pulse energies and durations The spotsize measurements with Kapton film indicated that a minimum thickness is necessary in order to obtain a cleanly burned through hole in the film and repeatability in the measurements. Kapton measurements with 125 µm film indicated that neither variations in pulse energy nor pulse duration affected the spotsize measurement. At small laser spotsize and low beam divergence the two measurement techniques yielded similar results. Conversely at larger spotsize and greater beam divergence the Kapton film measured spotsize was up to 30% larger than the Laserscope spotsize. Verification of the Kapton measurements with another method is warranted.