Stochastic processes associated with photophoresis

Types of photophoresis oriented to a field are induced by a body-fixed photophoretic force in combination with a restoring torque, related to gravitational, magnetic or electric field. The motion of a particle generally consists of the superposition of a systematic helical with a random, light-dependent component. This paper is concentrated on the stochastic part. Estimates of Brownian motion contributions to irregular as well as field photophoresis (in particular for gravito-photophoresis) are presented.