Condensation aerosol counting of guided particle by a single-charged Bessel-Gaussian beam as an optical tube

Abstract

In this study, a new method of condensation particle counting, CPC, using optical guiding of micro particles was developed. Optical forces (e.g., radiation pressure and photophoretic force) can guide particles in directions that are of the order of their diameter. Optical forces on micro particles by radiation of a donut shaped beams such as first order Laguerre- Gaussian, LG01, and single-charged Bessel-Gaussian, BG01, beams are investigated. The movement of aerosols that irradiated by these beams are simulated. In experiments, the microscopic aerosols are trapped along a BG01 beam axis and guided to the measuring space where a second beam is focused. Due to decrease in particle diffusivity, most of them can pass in focused light. As a result, the lights scattered by micro particles have sufficient intensity for detecting. This is even more important as the particles get smaller. Experimentally, by guiding aerosols less than 3.5 µm in a BG01 beam as an optical tube, about 18% increase in condensation counting of them was obtained.