Dipole-dipole Interaction Of Two Optically Levitated Nanoparticles In Vacuum

Since its invention,optical tweezers technology has developed rapidly.It can manipulate micro or nano scale objects in a non-contact way,and is often widely used in life science,colloidal physics,microfluidics and other fields as a super-sensitive force detector.In recent years,vacuum optical tweezers have become a hot spot in the study of photomechanics.The advantage of vacuum optical tweezers is that it can isolate the external environment well.The interaction between trapped particles and the environment only comes from the random collision with the remaining air molecules in the vacuum.Secondly,the motion state of the light-captured particles can be detected in real time with high precision by using position measurement techniques such as pre-scattered light interferometry.Its appearance greatly improves the detection sensitivity of the system,and shows great application potential in the field of precise measurement of physical quantities such as force,heat and mass.The research of optical tweezers mainly focuses on five aspects,namely,particle delivery,position detection,the cooling of the movement of the center of mass,the study of manipulating various kinds of objects and multi-beam optical trap.This dissertation focuses on the study of multi-beam optical trap and based on the system of optically levitated nanoparticles,we investigate the effect of the trapping beam with different polarizations on the scattering-induced dipole-dipole interaction of two nanoparticles in vacuum.we experimentally realize a stable trap of nanoparticles using the strongly focused laser beam in vacuum.We use the detection system to detect the motion signals of the nanoparticles.The mass and size of the nanoparticles are derived.Splitting a laser beam into two beams through a polarizing beam splitting prism,we individually trap two nanoparticles using two strongly focused lasers in vacuum and study the scattering-induced dipole-dipole interaction of the particles.The frequencies of the center-of-mass(Co M)motion and torsional vibration versus the trapping powers near the degeneracy points are measured under different polarizations for the trapping beams.The interaction of the torsional vibrations is not observed in this experiment,which indicates that the dipole scattering almost can’t influence this motion mode.On the contrary,a strong coupling between the Co M motions occurs when the polarizations of the trapping beams are perpendicular to the line between the two particles.The measured coupling strength is 1.6k Hz.To sum up,we study the scattering-induced dipole-dipole interaction of the two optically levitated nanoparticles,and discuss the influences of the polarization and power of the trapping beam,as well as the distance between the nanoparticles on the coupling strength.It is helpful for the further study on the collective motion of scattering-induced dipole-dipole interaction of nanoparticles and collaborative cooling and manipulation of multi-particle systems.