Real-time holographic interferometry is used to examine the thermal interaction between a propagating beam of CO2 laser radiation and an absorbing gas. For the first time, the effect of convection has been eliminated in such a system through the use of reduced gravity conditions as obtained aboard the NASA KC-135 microgravity aircraft. Under these conditions absorption of laser radiation yields interference fringes with a quasi-Gaussian profile reflecting the irradiance profile within the laser beam. A theoretical model of this convectionless interaction is proposed using the linearized hydrodynamic equations. A good fit to the finite fringe data was obtained under a variety of experimental conditions, although we find that thermal conduction may become important at high irradiance.

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