A self-calibrating optomechanical force sensor with femtonewton   resolution
  We report the development of an ultrasensitive optomechanical sensor designed to improve the accuracy and precision of force measurements with atomic force microscopy. The sensors reach quality factors of 4.3x10^6 and force resolution on the femtonewton scale at room temperature. Self-calibration of the sensor is accomplished using radiation pressure to create a reference force. Self-calibration enables in situ calibration of the sensor in extreme environments, such as cryogenic ultra-high vacuum. The senor technology presents a viable route to force measurements at the atomic scale with uncertainties below the percent level. 
John Melcher, Julian Stirling, Felipe Guzman Cervantes, Jon R. Pratt,   Gordon A. Shaw
cond-mat.mes-hall