Research On Capturing Gold Nanoparticles By Femtosecond Optical Tweezers

When light is incident on an object,an exchange of energy and momentum occurs between the object and the light.The object is subjected to a force,which produces the mechanical effect.This effect is the basis of the optical tweezers principle.Optical tweezers control particles in a non-contact manner,so as to achieve noninvasion manipulation and real-time tracking.Therefore,optical tweezers are widely used in physics,nanomaterials,biology and other areas.In this paper,the nonlinear optical effects of gold nanoparticles captured by femtosecond optical tweezers are studied.By constructing the illumination light paths,front and side image of the trapped metal nanoparticles were obtained.By comparing the trapping phenomenon in continuous light and femtosecond pulsed light,it is concluded that,unlike continuous light,trap splitting occurs in pulsed laser mode.Secondly,by using different numerical aperture objectives to capture gold nanoparticles,the relationship between the splitting distance of gold nanoparticles,the numerical aperture of the objective lens,and the optical power in the femtosecond pulsed laser mode is obtained.When the laser is circularly polarized,we compare the change of the splitting distance of gold and silver nanoparticles.In terms of theory,based on the vector diffraction theory,the focus fields in different laser working modes are calculated and the focus field of linearly polarized light is obtained.The focus field and nonlinear polarization potential energy field under linearly polarized light were simulated using MATLAB software.