Cold Brownian motion in aqueous media via anti-Stokes photoluminescence

Advances in cryogenic sciences have enabled several observations of new low-temperature physical phenomena including superconductivity, superfluidity, and Bose-Einstein condensates. Heat transfer is also critical in numerous applications including thermal management within integrated microelectronics and the regulation of plant-growth and development. Here we demonstrate that single-beam laser-trapping can be used to induce and quantify the local refrigeration of aqueous media through analysis of the cold Brownian dynamics of individual Yb3+-doped yttrium lithium fluoride (YLF) crystals in an inhomogeneous temperature field via forward light scattering and back-focal-plane interferometry. A tunable, NIR continuous-wave laser is used to optically trap individual YLF crystals with an irradiance on the order of 1 MW/cm2. Heat is transported out of the crystal lattice (across the solid / liquid interface) by anti-Stokes photoluminescence following upconversion of Yb3+ excited states mediated by optical-phonon absorption. The cold Brownian motion (CBM) analysis of individual YLF crystals indicates local cooling by >21 C below ambient conditions suggesting a range of potential future applications.