Optical pulling is the attraction of objects back to the light source by the use of optically induced “negative forces”. The light-induced 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. Here, we demonstrate that micron-sized absorbing particles can be optically pulled and manipulated towards the light source over
a long distance in air with a collimated Gaussian laser beam based on a negative photophoretic force. A variety of airborne absorbing particles can be pulled by this optical pipeline to the region where they are optically trapped with
another focused laser beam and their chemical compositions are characterized with Raman spectroscopy. We found that
micron-sized particles are pulled over a meter-scale distance in air with a pulling speed of 1-10 cm/s in the optical pulling pipeline and its speed can be controlled by changing the laser intensity. When an aerosol particle is optically
trapped with a focused Gaussian beam, we measured its rotation motion around the laser propagation direction and
measured its Raman spectroscopy for chemical identification by molecular fingerprints. The centripetal acceleration of
the trapped particle as high as ~20 times the gravitational acceleration was observed. Optical pulling over large distances
with lasers in combination with Raman spectroscopy opens up potential applications for the collection and identification
of atmospheric particles.
Gui-hua Chen, Lin He, Mu-ying Wu, Guang Yang, and Y. Q. Li, "Optical trapping, pulling, and Raman spectroscopy of airborne absorbing particles based on negative photophoretic force," Proc. SPIE 10347, Optical Trapping and Optical Micromanipulation XIV, 103472A (Presented at SPIE Nanoscience + Engineering: August 10, 2017; Published: 25 August 2017); https://doi.org/10.1117/12.2276972.
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