Study Of Photo-assisted Dielectric Microdroplet Manipulation Mechanism Based On Lithium Niobate

Photo-assisted dielectric microdroplet manipulation based on Li Nb O₃ is a novel non-contact manipulation technology which utilizes the virtual electric field induced by laser illumination.It overcomes the shortcomings of traditional manipulation methods,becoming a promising manipulation technique.But the study about the photo-assisted dielectric microdroplet manipulation is not sufficient by now.For example,the dielectric microdroplet manipulation based on y-cut lithium niobate is still not reported.The study of combination of photoelectricity and pyroelectricity is relatively few,and most studies of microdroplet manipulation are carried out at room temperature.In this thesis,the above issues are investigated.Firstly,the photo-assisted microdroplet manipulation behaviour based on y-cut Li Nb O₃ crystals is studied.Two sandwich structures are tried:y-cut Li Nb O₃ to quartz sandwich structure(Case1)and y-cut Li Nb O₃based anti-symmetrical sandwich structure(Case2).In the two cases,we study the dynamic processes of dielectric microdroplet deformation.The results show that,in Case1 microdroplet deformation is caused by the illumination,and then the microdroplet goes to the-c side of y-cut Li Nb O₃crystal.However,in Case2,upon the focused laser irradition the microdroplet starts to deform gradually,changes from the initial round shape to a dumbbell-like one,and finally splits into two subdroplets with similar sizes,without any external help of other effects.It is found that the splitting time increases with the increasing gap of sandwich structure and the initial size of microdroplet,but decreases with the increasing laser intensity.And at the fixed illumination intensity,the threshold of the electric field required of microdroplet splitting goes up with the increasing of the gap of sandwich structure and the initial size of microdroplet,as well.Secondly,the photo-assisted microdroplet manipulation mechanism based on y-cut Li Nb O₃ crystals is studied.With the help of the numerical simulation,the characteristics of the microdroplet deformation and splitting in the two cases are analysed.Two problems cause the failure of microdroplet splitting in Case1:one is the volume force provided by a single Li Nb O₃ substrate is not sufficient for the microdroplet splitting.More importantly,the unbalanced drag forces induced by the dipolar photovoltaic field easily makes a large part of microdroplet deviate from the splitting position and finally leads to the failure of the microdroplet splitting.And we also analysed the process of microdroplet splitting,which matches the experimental results very well.Finally,the photo-assisted microdroplet manipulation behavior and mechanism based on c-cut Li Nb O₃ crystals is studied,which includes the dielectric microdroplet array at normal temperature and the microdroplet manipulation by utilizing the photovoltaic and pyroelectric effects of Li Nb O₃ at about 40?.We find that with the help of defocusing and focusing of objective the dielectric microdroplet can be split into smaller droplets array and merged flexibly.And we also realize the parallel transportation of microdroplet array by laser scanning on the chip.In addition,we achieve the fixed-axis rotation and reciprocating motion of dielectric microdroplet at about 40?.