Optical levitation of 10-ng spheres with nano-g acceleration sensitivity

We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 ng. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 x 10(-6) g/root Hz for a 12-ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (-0.7 +/- 2.4 [stat] +/- 0.2 [syst]) x 10(-9) g is measured in 1.4 x 10(4) s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.