Development And Related Research Of Holographic Optical Tweezers System

Optical tweezers technology is the product of the interaction of light with matter.It can manipulate micro/nanoscale objects in a non-contact manner and allows force detection on the scale of picoNewton level,and the detection accuracy can even reach femtoNewton level,so it is commonly used as ultra-sensitive force detectors and widely applied in life sciences,colloid physics,microfluidics and other fields.The research of optical tweezers mainly focuses on four aspects,namely,position detection,trap stiffness calibration,beam shaping and the study of manipulating vari-ous kinds of objects.This dissertation focuses on these four points and aims to build a versatile optical tweezers system.It is expected that this system could realize the cap-ture,manipulation and application research of objects of interest in a more flexible and controllable manner.Focusing on the above research goals,two means of constructing optical tweezers system have been gradually achieved:through conjugate design of external optical path,the trapping beam controlled by a reflecting mirror was successfully introduced into the rear aperture of the objective mounted on a commercial microscope(Nikon Eclipse Ti-U)to manually achieve two dimensional manipulation of polystyrene spheres;an open single-beam optical trapping system and microscopic imaging device were de-signed and constructed on our own,and its physical parameters were calibrated.Using this trapping system,we captured mouse myoblasts and achieved their passive control.Based on those early studies,main research works of this dissertation are as follows:(1)A varying frequency sinusoidal stimulus method was proposed to explore dynamics of particles in optical traps,and the frequency selection problem therein was clarified,and the relationship between particle amplitude and phase delay was theoretically ex-pounded to follow a cosine form;it was confirmed through experiments that merely using low-bandwidth detectors sufficed to obtain particle amplitude and phase delay if Nyquist-Shannon sampling is met,so it can therefore reconstruct force field within particle's radius;on the other hand,the effect of polarization on particle escape was discussed,and it was found that the critical amplitude or frequency had sinusoidal rela-tionship with the polarization direction of trapping beam.(2)Optimizing the imaging quality via focused illumination and designing 4f configuration to introduce a spatial light modulator into trapping path,we successfully built a multi-functional holographic optical tweezers(HOTs)system.Programs based on Collins formula and ABCD ma-trix were wrote to promote researches on computer-generated holograms(CGH)and special light propagation properties.Taking the piezoelectric displacement platform as the reference and using grating phase generated by computer determined the effective focal length of the system,which was in perfect agreement with the result calculated by geometric optics,indicating that the HOTs system meet the design expectation.We detailed various kinds of classical CGH algorithms,and utilized the superposition of prism and lens algorithm to create 3 × 3 point array,and finally simultaneously cap-tured 9 polystyrene spheres of 4 ?m diameter.(3)A phase encoding strategy based on complementary random binary mask was proposed and used to produce multiple point traps of distinct energy ratio at specified sites in trapping plane.Based on the con-structed HOTs system,four sets of regulating experiments were conducted to demon-strate that the proposed strategy has capabilities to separately regulate trapping power ratios between optical traps under multi-objects manipulation tasks by both calibrating trap stiffness and directly measuring trapping power,thus verifying the effectiveness and repeatability of the proposed energy regulating method.In addition,three optical traps with specifically designed energy ratio were decorated with vortex beams of dif-ferent topological charges to control rotational direction and speed of trapped particles,thus confirming the multi-functionality of the strategy.