Conventional methods of manipulating particles with light, such as optical tweezers and optical tractor beams, rely on beam-shaping to realize complex electromagnetic field profiles and are thus sensitive to scattering. Here, we show that, by introducing tailored optical asymmetry in the particle, we can realize a novel guiding method that is controllable by the frequency of light, without regard to the direction or the shape of the light beam. With detailed stochastic simulations, we demonstrate guiding of a two-faced nanoparticle where the optically induced thermophoretic drift serves as the propulsion mechanism. Exploiting the difference in resonant absorption spectra of the two materials, we create a bidirectional local thermal gradient that is externally switchable. This is advantageous because the frequency of a light beam, unlike its shape or coherence, is preserved even in strongly scattering environments. Since this approach is insensitive to scattering and applicable to many particles at once, as well as particles that cannot be optically resolved, it may enable useful applications in biology, microfluidics, in vivo tasks, and colloidal science.
Bibliographical noteFunding Information:
This work was partially supported by the Army Research Office through the ISN under Contract No. W911NF-13-D-0001, and by the MRSEC Program of the NSF Under Award No. DMR- 1419807. The research of I.K. was also partially supported by the Seventh Framework Programme of the European Research Council (FP7-Marie Curie IOF) under grant agreement no. 328853-MC-BSiCS. H.B. acknowledges support from the QuantiXLie Center of Excellence.
- Janus particle
- optical guiding
- optical scattering
- spectral selectivity