Measurement of Particle Density in a Dusty Plasma by a Single-Pass Laser Extinction Method

Summary form only given. Measurement of dust particle density was performed using the single-pass laser extinction method, in which particle density was obtained using the relation between particle density and the difference between two He-Ne laser beam intensities with and without passing a dusty plasma. The dusty plasma was prepared by externally-injecting known-sized (65 nm-3 mum) mono-disperse SiO₂ or melamine formaldehyde particles into an argon DC discharge. Before applying the method to the dusty plasma, the measurement limit of the extinction ratio of the experimental setup and the accuracy of the calculated scattering cross-section were experimentally investigated using a solution of the particles and distilled water. The measurement limit was about 1% with the current single-pass system, and the lowest measurable particle density in the argon dusty plasma was about 10⁴ cm^-3 for 1.5 mum radius particles. It is expected to be improved by removal of dusts floating in the air in the laser path and employing a multi-pass system that is under preparation