Optical Levitation and Refrigeration of Yb:CaF2 Microparticles for Precision Sensing

Particles confined by optical tweezers have been shown as sensors for gravity waves, dark matter interactions, and accelerations. Parasitic background absorption of the laser light in these experiments results in elevated internal temperatures of the particle, which impose limits on particle size and can contribute to black body radiation pressure shot noise. Such limits restrict the sensitivity of these sensors. Additionally, optically levitated nanoparticles show theoretical promise as testbeds for mesoscopic matter-wave interferometry, but elevated internal particle temperature may limit coherence times. Optical refrigeration and the minimization of parasitic background absorption may provide a solution to the problem of elevated particle temperatures. Previous research in levitated optical refrigeration has utilized nanoparticle fragments with both intrinsic and shape induced birefringence, which can create unwanted motional modes and complicate sensing. In pursuit of a solution to these challenges we report a novel levitated particle optical refrigeration experiment, successfully cooling the internal temperature of non-birefringent, spherical, Yb:CaF2 microcrystals utilizing dual beam optical tweezers.