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Optical power tolerance on micromirrors is a critical aspect of many high-power optical systems. Absorptive heating can negatively impact the performance of an optical system by altering the micromirror's curvature during operation. This can lead to shifts in the beam waist locations or imaging planes within a system. This paper describes a scheme to measure the impact of mirror heating by optical power and determine the power tolerances of micromirrors with gold and aluminum coatings using a 532-nm laser. Results are compared with an analytical model of thermally induced stress and optical absorptive heating. Experimental data shows that gold-coated mirrors are able to handle 40 mW of optical power with a beam waist displacement of less than 20% of the output Rayleigh length, while aluminum-coated mirrors can tolerate 125 mW. Measured data along with modeling suggest that, with proper metal coating, optical powers greater than 1 W should not adversely affect the system performance.