Improving the longitudinal and radial forces of optical tweezers: A numerical study

Usually, optical tweezers are based on the focusing a Gaussian laser beam giving rise to a diffraction-limited spot. An alternative has been proposed by several authors which consists to enlighten the trap by a high-order radial Laguerre-Gauss LGp0 beam. However, doing that leaves unchanged the longitudinal stability but improves several times the radial force with increasing the radial mode index p. In this paper, it is demonstrated, for a given power, that introducing a primary spherical aberration (SA) on the path of the incident LGp0 beam allows increasing several times both the longitudinal and transverse trapping effects. The best results are obtained for negative SA.