The temperature of an optically trapped, rotating microparticle

The measurement of temperature at the mesoscopic scale is challenging but important in a wide variety of research fields, including the investigation of single molecule and cell mechanics and interactions as well as fundamental studies in heat transfer and Brownian dynamics on this scale. In this letter we present a route that determines temperature at the nano- to microscale with three independent measurements performed on a single trapped, rotating luminescent microparticle. We measure temperature changes using both the internal and external degrees of freedom, via (i) the upconverted luminescence, (ii) the rotation rate, and (iii) the Brownian dynamics of the particle. This novel tripartite approach allows us to cross-correlate the temperature for both the internal and external (center-of-mass) degree of freedom for the particle. In addition, our approach provides a measure of the temperature increase without the need of a precise knowledge of the particle dimensions, shape or any previous calibration of the sample or the experimental set-up. The developed technique opens up prospects for stringent tests of nanothermometry.