Femtosecond pulse-width dependent trapping and directional ejection dynamics of dielectric nanoparticles
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AbstractWe demonstrate that laser pulse duration, which determines its impulsive peak power, is an effective parameter to control the number of optically trapped dielectric nanoparticles, their ejections along the directions perpendicular to polarization vector, and their migration distances from the trapping site. This ability to controllably confine and eject the nanoparticle is explained by pulse width-dependent optical forces exerted on nanoparticles in the trapping site and ratio between the repulsive and attractive forces. We also show that the directional ejections occur only when the number of nanoparticles confined in the trapping site exceeds a definite threshold. We interpret our data by considering the formation of transient assembly of the optically confined nanoparticles, partial ejection of the assembly, and subsequent filling of the trapping site. The understanding of optical trapping and directional ejections by ultrashort laser pulses paves the way to optically controlled manipulation and sorting of nanoparticles. © 2013 American Chemical Society.
SponsorsThe financial supports from the Ministry of Education of Taiwan (MOE-ATU Project; National Chiao Tung University), the National Science Council of Taiwan (Grant No. NSC 100-2113-M-009-001), and Foundation of the Advancement for Outstanding Scholarship of Taiwan to H.M. are gratefully acknowledged.
PublisherAmerican Chemical Society (ACS)