AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Optical Pulling of Single Aerosol Particles over a Meter-Long Distance Using a Single Laser Beam
Adam Hart, Joshua Mangum, YONG-QING LI, East Carolina University, Department of Physics
Abstract Number: 39 Working Group: Single Aerosol Particle Studies - Fundamentals
Abstract Capture and transportation of small objects in air using lasers are attractive for the collection and analysis of single aerosol particles and biological aerosols. Optical pulling is the attraction of objects back to the light source by the use of optically induced “negative forces”. It is commonly expected that when illuminated by a light beam, an object will be accelerated along the light propagation direction by radiation pressure. The idea of using laser beams to attract objects back to the light source is counterintuitive and has long been attractive to scientists. Here, we demonstrate the first experiment that micron-sized absorbing aerosol particles can be optically pulled and manipulated over a meter-scale distance with a collimated laser beam based on negative photophoretic force. The laser-induced negative photophoretic force is generated by the momentum transfer between the heating particles and surrounding gas molecules and can be several orders of magnitude larger than the radiation force and gravitation force. This force can force the aerosol particles moving against the laser propagation direction. We found that micron-sized particles are pulled towards the light source at a constant speed of 1-10 cm/s in the optical pulling pipeline while undergoing transverse rotation at 0.2-10 kHz. The moving speed of individual particles can be controlled by changing the laser intensity. A variety of micro-sized particles including carbon nano-clusters, smut biological cells, iron filings and copper oxide powders can be pulled by this optical pipeline to the region where they are optically trapped and their chemical compositions are characterized with Raman spectroscopy. Optical pulling over large distances with lasers in combination with Raman spectroscopy opens up potential applications for the collection and analysis of single aerosol particles in low-pressure environments.