Description
When confined in a horizontally near-flat potential well in the plasma sheath region, microparticles are very sensitive to perturbations in their horizontal force balance. In this contribution we present experiments where glass microparticles confined in the sheath region of a radio frequency driven parallel plate argon plasma, react to laser light hitting surfaces near the potential well. The bottom electrode in this configuration has a shallow groove to create a potential well to confine the microparticles. When the sides of this groove are illuminated, the confined microparticles move away from the illuminated area. This displacement caused by the interaction of the light and the electrode is unexpected as the energy of the laser photons are well below the work function of the illuminated electrode surface.
To find an explanation for these observations, multiple parameters have been varied. In the presented experiments variations in laser wavelength, surface material, illumination direction, and surface geometry were considered. The confined microparticle displacement is dependent on the wavelength of the light, and stronger displacement is seen for higher intensities. Furthermore, the location and direction of illumination also influence the amount of displacement together with the surface geometry. The results of these experiments are presented, along with hypotheses for possible explanations of the observed effect and plans for future research to understand this phenomenon.