Influence of the beam divergence on the exerted force on a sphere by a laser beam and required conditions for stable optical levitation

From a geometric optics approach, we present an evaluation of the axial and transverse components of the radiation pressure force exerted on a sphere by a divergent or convergent laser beam. The calculation performed for a hollow dielectric sphere is easily applied to solid dielectric spheres and to metallic ones. The energy distribution in the laser beam, chosen according to applications, corresponds to either TEM ₀₀ or TEM ^∗₀₁ laser transverse modes. Tables of values representing the force evolution with the beam divergence lead to stability conditions required for optical levitation and also give the magnitude of the forces exerted by the beam on the sphere.