Displacement Calibration of Optical Tweezers With Gravitational Acceleration

In recent years, levitated particles of optical traps in vacuum have shown the enormous potential for precision sensor development and new physics exploration. However, the accuracy of the sensor is still hampered by the uncertainty of the calibration factor relating the detected signal to the absolute displacement of the trapped particle. In this paper, we suggest and experimentally demonstrate a novel calibration method for optical tweezers based on free-falling particles in vacuum, where the gravitational acceleration is introduced as an absolute reference. Our work provides a calibration protocol with a great certainty and traceability, which is significant in improving the accuracy of precision sensing based on levitated optomechanical systems.