  The superposition of a Gaussian mode and a Laguerre-Gauss mode with
$\ell=0,p\neq0$ generates the so-called bottle beam: a dark focus surrounded by
a bright region. In this paper, we theoretically explore the use of bottle
beams as an optical trap for dielectric spheres with a refractive index smaller
than that of their surrounding medium. The forces acting on a small particle
are derived within the dipole approximation and used to simulate the Brownian
motion of the particle in the trap. The intermediate regime of particle size is
studied numerically and it is found that stable trapping of larger dielectric
particles is also possible. Based on the results of the intermediate regime
analysis, an experiment aimed at trapping living organisms in the dark focus of
a bottle beam is proposed.
