Laser Heating of 2-D Dusty Plasmas Using a Random Arc Pattern

A laser heating method for 2-D dusty plasmas is improved so that particle motion better resembles thermal motion in a liquid. Laser beams are rastered in a pattern of arcs with three randomly varying parameters: curvature, initial angle, and the speed of the laser footprint as it follows an arc. An experimental test is performed using particle tracking to generate power spectra of velocities. Peaks in these spectra indicate coherence in the particle motion, which is a discrepancy when compared with the stochastic nature of molecular motion in a liquid. We find that spectral peaks are diminished tenfold by rastering with random arcs as compared with a previously used pattern in which beams moved in straight lines at constant speeds.