Internal electric field distribution within a micro-cylinder-shaped particle suspended in an absorbing gaseous medium

The present study is concerned with photophoresis of a microsized long cylinder-shaped particle suspended in an absorbing gas medium. To facilitate the analysis, an infinite cylinder subjected to an intensive light beam is considered as the physical model. The electromagnetic energy can be absorbed by the particle and turned into thermal energy heating surface unevenly, which results in a net momentum transfer between gas molecules and the particle to drive particle in photophoretic motion. Effects of the governing parameters on the absorbed energy distribution in the cylindrical particle are investigated. The results demonstrate that increasing either the radius or absorptivity of the cylinder enhances the energy absorbed on the illuminated side and tends to generate positive photophoresis; while an increase in the refractivity of the particle tends to enhance the internal electric field intensity and shift the absorption peak on the shaded side toward the particle center. Increase in medium absorptivity reduces the energy reaching at the particle, which significantly degrades the level of energy absorption and therefore weakens the photophoretic mobility of the particle. It is also found that, at the same conditions, the source function peaks in long cylinder-shaped particles are generally lower than those in spheres due to the weaker light refraction of the cylindrical shape.