Measurement of the thermal contribution to the nonlinear refractive index of air at 1064 nm

The thermal contribution to the nonlinear refractive index of air at 1.064 mu m was measured with a high-finesse Fabry-Perot cavity and a 500-mW cw laser beam. At room temperature and pressure, the nonlinear refractive-index coefficient of air was found to be n(2)((th)) = (-1.9 +/- 0.2) x 10(-14) cm(2)/W for a beam waist radius of 0.23 mm and was found to be independent of the relative humidity. The thermal nonlinearities of N-2, O-2, and CO2 were also measured, and it was found that the dominant contribution to air is its O-2 content. (C) 2000 Optical Society of America. OCIS codes: 190.0190, 120.2230.