Measurement of localized heating in the focus of an optical trap

Localized heating in the focus of an optical trap operating in water can re sult in a temperature rise of several kelvins. We present spatially resolve d measurements of the refractive-index distribution induced by the localize d heating produced in an optical trap and infer the temperature distributio n. We have determined a peak temperature rise in water of 4 K in the focus of a 985-nm-wavelength 55-mW laser beam. The localized heating is directly proportional to power and the absorption coefficient. The temperature distr ibution is in excellent agreement with a model based on the heat equation. (C) 2000 Optical Society of America OCIS codes: 170.4520, 120.3180.