Research On Micro/nano Particle Manipulation And Thermal Conduction Physics Based On Optomechanics

Optomechanics studies the mechanical effects in the interaction of light and matter and their applications.One of the important research fronts is the cooling and manipulating of the center of mass motion of mechanical oscillators and micro-nano particles.With cavity cooling,the center of mass motion of the mechanical oscillators and nanoparticles has been successfully cooled to quantum ground state,paving a way to the exploring of macroscopic quantum mechanics,developing of high-precision measurement technology,and manufacturing of highly sensitive sensors.Currently,some new research directions in optomechanics are emerging.Such as(a)cooling microparticles that are larger and heavier than nanoparticles,for exploring quantum gravitational physics and the transition from quantum to classical physics,and developing higher-precision interferometric technology;(b)studying the optical acceleration of dielectric particles to provide new methods of depositing,manipulating and transporting nanoparticles for industrial and medical applications;(c)invesgating of the cross-application of optomechanics and statistical physics.After analysis of the development trends of optomechanics,this thesis has carried out research on laser cooling and acceleration of micro and nano particles and proposed a theoretical scheme for testing low-dimensional thermal conduction with optomechanical systems.The main results are:1.We propose polarization gradient cooling of charged and neutral microspheres(MSs).Applying two counterpropagating optical fields of different polarizations at reddetuned Mie resonance to alternatively excite two degenerate WGMs in a moving microsphere,the microsphere can feel different optical poteantial and optical damping force in these two degenerate WGMs.The variation of the polarization of the light filed excites the two WGMs in turn,making them to alternatively play dominant roles in cooling.Moreover,we investigate the effects of electric affinity of a charged microsphere on cooling.Our numerical simulation shows that cooling temperature less than 1m K could be achieved for big MSs.By optimizing parameters such as optical frequency,light intensity,and microsphere radius,the cooling limit temperature can be further reduced.Compared with the current optical feedback cooling method used for cooling microspheres,our method can be used to cool the microspheres in free space without a feedback cooling system,opensing up a new way for the cooling microspheres.2.We propose the optical lattice acceleration of nanoparticles.An accelerated optical lattice is used to trap a nanoparticle and accelerate it with the lattice.In the process of acceleration,the influence of air resistance needs to be take into account.We find that in the reference frame accelerating with the optical lattice,the trapping nanoparticle is in a tilted equivalent optical lattice potential duo to the inertial force and the air resistance.As time increases,the depth of the equivalent optical lattice potential well decreases.The trapping and stable acceleration of a nanoparticle not only requires that the initial kinetic energy of the nanoparticle to be less than the initial depth of the optical lattice potential,but also requires the acceleration time to be shorter than the disappearance time of the equivalent potential well.Moreover,the absorption of light by nanoparticles also have an important impact on the acceleration.The light intensity that can melt the nanoparticles after a long time absorbing is called melting critical intensity.In order to keep the microsphere from melting,the light intensity should less than the melting critical intensity or the acceleration time should less than the time required for the melting when the light intensity is larger than the melting critical light intensity.Numerical simulations show that using a laser with intensity higher than the melting critical intensity for acceleration,a nanoparticle can reach the velocity about kilometers per second within a microsecond-scale time length and a millimeter-scale space length,and the internal temperature hardly rise.Our proposal provides a new way for deposition,manipulation and transportation of nanoparticles in industry and medicine.3.We propose to apply two cavity optomechanical systems at unequal effective temperatures respectively to couple to two ends of a chain of harmonic oscillators for investigating heat transport problems in low-dimensional systems.In this model,the two cavity optomechanical systems at both ends can function as thermal reservoirs that can be engineered by driving laser.The heat flux approaches to a constant value as the chain length increases,showing breakdown of the Fourier's law in this system.We find that the magnitiude and direction of the heat flux can be controlled by the driving lasers.Futhermore,the heat flux can be switched on and off by controlling the on-site potential in the harmonic chain,which provides a new idea for the manufacture of thermal switches and thermal triodes.Finally,we developed the theory of measuring heat flux by using the correlation of the two mechanical oscillators in the cavity-optomechanical systems.Our research not only can help people getting a deeper understanding of the interaction between light and micro-nano particles,but also shows the new use of optomechanics in testing non-equilibrium statistical physical theory.Furthermore,laser cooling and trapping of microspheres could pave a way for studying quantum-classic crossover and macroscopic quantum mechanics with potential application in quantum technologies.