An expression for a circularly polarized Gaussian laser beam is obtained from the electromagnetic vector potential A, of which the scalar part becomes the complex-source-point spherical wave. Based on the theory of laser-beam scattering by a stationary homogeneous sphere, the analytical formulas are derived for the optical torque components exerted on the levitated sphere in the circularly polarized focused laser beam. The optical torque is numerically calculated, and interpretations of the results are presented. For a sphere with size parameters ρ = (2πα/λ) = 10π and complex refractive index N = 1.47 + i0.000001, levitated at the center of a 1-W Ar+ laser beam, the z component of angular velocity in air ωrot,z is found to be about 4.0 rad/sec.
© 1985 Optical Society of America
Soo Chang and Sang Soo Lee, "Optical torque exerted on a homogeneous sphere levitated in the circularly polarized fundamental-mode laser beam," J. Opt. Soc. Am. B 2, 1853-1860 (1985)