Propagation characteristics of radially shifted Gaussian beams and their radiation forces on Rayleigh particles

A new kind of strictly Gaussian-shaped dark hollow beam (DHB), called radially shifted Gaussian beam (RSGB), is proposed in this paper. Compared with previous approximately Gaussian-shaped DHB [i.e., Hollow Gaussian beam (HGB) and hollow sinh-Gaussian beam (HsGB)], it is much more convenient to design any special sized DHB by using RSGB. The propagation characteristics of RSGB, especially its autofocusing property, are investigated in detail and compared with that of HGB and HsGB under the same condition. It is found that the hollow region of RSGB can remain for a longer distance; and its autofocusing property is much stronger. An analytical expression for the focal position is also obtained for Gaussian-shaped DHB for the first time. Radiation forces of these beams exerted on two kinds of Rayleigh particle are analyzed. Numerical results show that RSGB also has advantages over previous Gaussian-shaped DHB in two-dimensional optical micromanipulation. For the low-index particle, RSGB can trap it for a longer distance; for the high-index particle, RSGB can produce a larger trapping force at the focal point.