To construct a stable and tunable optical trap in the focal region of a high numerical aperture lens

Based on the diffraction theory, the focusing properties of a radially polarized quadratic Bessel-Gaussian beam (QBG) with on-axis radial phase variance wavefront are investigated theoretically in the focal region of a high numerical aperture (NA) objective lens. The phase wavefront C and pupil beam parameter mu of QBG are the functions of the radial coordinate. The detailed numerical calculation of the focusing property of a QBG beam is presented. The numerical calculation shows that the beam parameter mu and phase parameter C have greater effect on the total electric field intensity distribution. It is observed that under the condition of different mu, evolution principle of focal pattern differs very remarkably on increasing C. Also, some different focal shapes may appear, including rhombic shape, quadrangular shape, two-spherical crust focus shape, two-peak shape, one dark hollow focus, two dark hollow focuses pattern, and triangle dark hollow focus, which find wide optical applications such as optical trapping and nanopatterning. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)