WIDG Seminar: Wenqiang Li, Yale, “Thermal effects and stability of optically levitated micron-sized spheres in vacuum”

The optical trapping and manipulation of micron-sized dielectric spheres can enable a variety of measurements including sub-attonnewton force sensing and precision torque sensing. These sensors can be used to search for new forces that deviate from Newton’s or Coulomb’s laws, which arise in certain models of new physics that attempt to account for the nature of gravity, dark matter, or dark energy. To thermally isolate the sphere from the room-temperature environment, spheres are optical levitated in high vacuum. However, in high vacuum heating of the sphere’s motion by the laser prevents trapping by a standard optical tweezers unless an active feedback system is employed to maintain the trap stability.
In this talk, the reason for loss of the sphere in high vacuum when feedback is not used is analyzed. We study the thermal effects acting on the sphere at high vacuum, including the photophoresis force and temperature induced center-of-mass motion. In addition, heating due to the laser pointing noise is analyzed.