Tham khảo tài liệu 'micromechanical photonics - h. ukita part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Theoretical Analysis 91 Fig. . Geometry for calculating axial trapping efficiency of polystyrene mi-croshere. The laser focus is on the optical axis which is parallel to the center line of the microsphere b Fig. . Geometry for calculating the transverse trapping efficiency of polystyrene microshere. The laser focus is located along the transverse center line of the sphere a Trapping efficiency Focus point Fig. . Total trapping efficiency Qt exerted on a polystyrene microsphere suspended in water by trap with a uniformly filled input aperture of NA for axial a and for transversal b dioc-lfuis 92 3 Optical Tweezers Table . Maximum trapping efficiency for axial trap with various laser beam profiles beam profile downward directed upward directed Gaussian TEMoo uniform donut TEM01 the upward directed beam is more effective in trapping the microsphere than the downward-directed beam. Table shows microsphere materials for the analysis in this book. The trapping effidency d x iid iic on he inddnni an elo of a yiy Iieenis that trapping effidancy is reaated to the profUe of the aaeer baam. Tabk 3d shows the maximum trapping Hi i ccv viUiil -e l for input bamms wifli various mode intensity profiles Gaussian uniformly filled and donut. The maximum Q increases as the outer part intensity increases. Good trapping ÍS possible when the outer part of the aperture is filled by a high intensity to give a laser beam with a high convergence angle. Example . Calculate the axial trapping effidancy for a mierosphere wlem the focus of the uniformly input laser beam is alongthe optical axis in the center line of the sphere. Solution. First we find the incident angle 61 r 3 of a ray entering the input aperture of the objective lens at the arbitrary point r 3 as shown in Fig. . Since axial trapping efficiency is independent on 3 due to axial symmetry we consider r-dependence for the 61 r 3 . The angle 3 r between .
