High-efficiency And Dynamic Generation Of Vectorial Optical Beams And Its Application In Optical Micro-manipulation

With the deep research of the interaction between optical beams and matters,ones have paid more attention to the accurate and efficient modulation over the amplitude,phase and polarization states in optical field.Depending on the production location,the methods for generating the vector beams are divided into two kinds of schemes-intracavity modulation and extracavity modulation.The vector beams generated by the first methods are powerful with high energy conversion efficiency,but their modes are fixed and are not easily changed.By contrast,the vector beams generated by the second methods are flexible and can be dynamically modulated according to the needs,however the energy conversion efficiency is low.In this paper,we focused on the two issues.The first issue is how to improve the energy conversion efficiency in the extracavity scheme,and the second issue is how to achieve arbitrary modulation of fully vectorial optical fields.Firstly,based on spatial light modulators(SLM)and the split-screen method,two highy-efficient methods for generation of vector beams are proposed.In the first method,a lateral displacement splitting prism is used to split fundamental-mode beam into two parallel beams and to combine two beams which passed through the SLM.Under the premise of accurate and arbitrary optical modulation,the efficiency of generating vector beams is improved into more than 30%by optimizing the splitting and combining process.In the second method,the vector beams are generated by using a polarizing beam-splitter(PBS).A new type of phase-only ultra high definition(UHD)GAEA-2 SLM,with 3840x2160 pixels,is applied in this scheme and the size of each pixel is 3.84 microns.We developed a new Sagnac interferometer composed of a PBS and a UHD SLM.A incident beam is split into a horizontally polarized component beam and a vertically polarized component beam via the PBS and then the two beams imping on the left and right half regions of the SLM so that they are loaded different phases.Via the same PBS,the two beams are coaxially superposed to yield desired vector beams.Three different types of vector beams are generated in experiment,including classical vector beams with cylindrical symmetry,locally linearly polarized vector beams with multiple polarization singularities,and high-order Poincare sphere vector beams.The experimental results confirm that,the two proposed method have a higher conversion efficiency by an order of magnitude than conventional extracavity schemes.Secondly the applications of vector beams in focal field shaping are studied in our research.According to the idea of generating perfect vortex beams and the inverse methods of focal field shaping,the perfect phase gradient focal fields with different shapes are designed,such as circle,square and "8" shapes.They are applied into optical micro-manipulation experiment to catch and drive the small polystyrene spheres,with diameter 3.2 microns,moving along the specific trajectory.The stability of controlling small polystyrene spheres to these focal fields is improved bycorrecting the orbital singularities in the square and "8" shape focal field.Finally,by extending scalar focus shaping to vector field cases,we proposed themethod for vector focus shaping in the three dimensional volume.A inclined ring,a three-dimensional Archimedes spiral and a combination with different types of three-dimensional cures are generated in experiment by using our method.