Optical Trapping Of Two Kinds Particles Of Different Refraction Indices

Optical tweezers is one kind of optical trapping technology. It makesuse of a high numerical aperture to focus the incident laser beam toachieve a spot several microns in radius. One can move and trapmicroscopic particles using the gradient force provided by the focusedbeam. American scientist A. Ashkin and his colleagues successfullytrapped and manipulated dielectric particles in the size range from severalmicrons to tens of nanometers in1986, using a high convergent laserbeam. After that, optical tweezers has experienced great developmentsand wide applications. Recently, this technology is becoming a more andmore important tool in research fields such as physics, chemistry,biomedical science, micromachining, and spectroscopy.In this thesis, the main contents consist of the following aspects: Thefirst chapter, beginning with the origin of optical trapping, introduces therecent developments of the theoretical research and experiment of theoptical trapping technology and presents the main theoretical models ofcalculating the trapping forces. The second chapter presents the vector diffraction theory for high NA lenses. It is presented in the third chapterthat using a double circular radial polarized light beam can improve thestability of the traps for two kind of particles of different refractionindices. The fourth chapter presents the simultaneous traps for a largeamount of particles mentioned in the third chapter using two opposingradial polarized light beams and angular polarized light beams. The fifthchapter gives the summaries and outlooks.The innovations of this thesis rest in: Firstly, the electromagneticfield of the double circular vortex polarized light is deduced by usingvector diffraction theory of high NA lenses. Secondly, characteristics ofthe focused field of double circular vortex polarized light are studied, andtraps for two kinds of particles of different refraction indices are achievedby changing the truncation parameter and vortex angle to generatedifferent bright spots and dark spots. The three dimensional trappingstability of these traps are better compared to previous ones. Thirdly, theoptical mechanism of the three dimensional bright and dark spotsgenerated by two opposing focused beam is studied and used to achievetrapping for a large amount of different particles.