Thermal blooming of continuous wave laser radiation

Abstract

An experimental investigation of the thermal blooming of a focused CW CO2 laser beam, under cross-wind and slewing conditions, is described. Measurements of thermal blooming were made for Fresnel numbers of approximately 7 and approximately 13 and distortion numbers up to approximately 24. These results are compared with the predictions of a computer code, and are shown to be in excellent agreement. Using this code the far-field intensity profiles for infinite Gaussian and annular laser beam spatial profiles have been calculated over a wide range of Fresnel and distortion number values. Using the scaling law IRel=1/(1+a psi hb), where IRel is the decrease in peak intensity of the far-field spatial profile due to blooming and psi h a phase integral, these calculations yield values for a and b of 0.0125 and 1.660, and 0.0178 and 1.301 for Gaussian and annular beams respectively.