Abstract: Optical trapping is a powerful technique for the controlled manipulation of particles with sizes in the micron, sub-micron and nanometre range1. Conventional optical tweezers using a single, strongly-focused laser beam to confine particles within the focal volume of ~1um3. Optical binding describes the self-organisation of microparticles and nanostructures in an optical field that occurs over long distances and extended areas arising from the multiple scattering of light. Here we present experimental schemes for the control of optically bounds structures in evanescent optical fields. The first relies on total internal reflection at an interface, where the evanescent field penetrates a short distance (comparable to, or less than the optical wavelength) above the interface. We show that this geometry, shown in Figure 1(a), gives rise to one- and two-dimensional optically ordered structures of microparticles and also of nanostructures immersed in the field, shown in Figure 1(b) – (d), and quantify the binding forces and structure geometries via video microscopy2,3.
|Figure 1: Optical binding of carbon nanostructures. (a) Set-up of the optical binding experiment; (b) Optically bound chain of carbono nanotube bundles; (c) When the laser beam is turned off the chain disintegrates; (d) Laser beam on, chain re-forms|
1. O. M. Maragò, P. H. Jones, P. G. Gucciardi, G. Volpe & A. C. Ferrari. 'Optical trapping and manipulation of nanostructures', Nature Nanotechnology 8 807-819 (2013)
2. M. Sergides, S. E. Skelton, E. Karczewska, K. Thorneycroft, O. M. Maragó & P. H. Jones. 'Optically bound particle structures in evanescent wave traps', Proc. SPIE 8458, Optical Trapping and Optical Micromanipulation IX, 84583C, doi: 10.1117/12.929612 (2012)
3. S. H. Simpson, P. H. Jones, O. M. Maragò, S. Hanna & M. J. Miles. 'Opticalbinding of nanowires in counter-propagating beams’, Proc SPIE 8810 Optical Trapping and Optical Micromanipulation X, 881026, doi: 10.1117/12.2024466 (2013)
4. S. E. Skelton, M. Sergides, R. Patel, E. Karczewska, O. M. Maragó & P. H. Jones. 'Evanescent wave optical trapping and transport of micro- and nanoparticleson tapered optical fibers', Journal of Quantitative Spectroscopy and Radiative Transfer 113 2512-2520 (2012)