Index of refraction turbulence effects on thermal blooming in laboratory experiments

A laboratory experiment has been carried out to determine the effect of index of refraction turbulence on thermal blooming for cw CO2 laser radiation. The turbulence is generated by the forced mixing of two gases of different indices of refraction; helium and nitrogen. The thermal blooming is obtained by adding small amounts of propylene to the mixture. The construction of the test cell and methods of measuring the turbulence are discussed in detail. The experimental results are compared with the root-sum-squared (RSS) theory, i.e., that the blooming and turbulence effects may be considered separately and that the total beam area is given by A = Ao + AB + AT, where AB and AT are the increase in the time-averaged area of the beam due to blooming and turbulence. Agreement is excellent for the particular case considered.