A simple technique for direct, high power laser beam profile measurement using thermal imagers

摘要

Measuring the profile of a laser beam is of critical importance, especially for high power laser systems. Althoughdifferent techniques exist to measure the beam profile, owing to the use of optoelectronic detectors or cameras, theyprimarily work at lower powers and require tapping and attenuating the beam. In this process, there is potential for thediagnostic system affecting the beam quality. In this work, we propose a simple technique which can measure the beamprofile at full power using a thermal imager without the need for additional optical components. The method involvestaking a thermal image of the beam while it is incident on an absorptive surface such as a thermopile head which is usedto measure optical power. In addition, a second image is taken using a focused incidence on the surface at low powers.The second image which is reused provides the point spread function. We then make use of the linearity of the heatequation which allows the deconvolution of the point spread function from the original image to obtain the actual beamprofile. In this work, we utilized the technique to directly analyze the beam profile at full power of a 100 W class fiberlaser and analyzed deviations from single-modedness. In addition, we utilized offset splices to few-mode fibers to launchhigher order modes at the 100W level and demonstrate their direct characterization of multimode nature of the profile.This technique provides a simple alternative, using instruments present in most laser labs for direct, high power laserbeam profiling.