Liu, LuluKheifets, SimonGinis, VincentCapasso, Federico2019-09-172016Liu, Lulu, Simon Kheifets, Vincent Ginis, and Federico Capasso. 2016. “Subfemtonewton Force Spectroscopy at the Thermal Limit in Liquids.” Physical Review Letters 116 (22). https://doi.org/10.1103/physrevlett.116.228001.0031-90071079-71141092-0145http://nrs.harvard.edu/urn-3:HUL.InstRepos:41371367We demonstrate thermally limited force spectroscopy using a probe formed by a dielectric microsphere optically trapped in water near a dielectric surface. We achieve force resolution below 1 fN in 100 s, corresponding to a 2 angstrom rms displacement of the probe. Our measurement combines a calibrated evanescent wave particle tracking technique and a lock-in detection method. We demonstrate the accuracy of our method by measurement of the height-dependent force exerted on the probe by an evanescent wave, the results of which are in agreement with Mie theory calculations.en-USJournal Article2019-09-1710.1103/PhysRevLett.116.228001