Pushing nanoparticles with light — A femtonewton resolved measurement of optical scattering forces

Abstract

Optomechanical manipulation of plasmonic nanoparticles is an area of current interest, both fundamental and applied. However, no experimental method is available to determine the forward-directed scattering force that dominates for incident light of a wavelength close to the plasmon resonance. Here, we demonstrate how the scattering force acting on a single gold nanoparticle in solution can be measured. An optically trapped 80 nm particle was repetitively pushed from the side with laser light resonant to the particle plasmon frequency. A lock-in analysis of the particle movement provides a measured value for the scattering force. We obtain a resolution of less than 3 femtonewtons which is an order of magnitude smaller than any measurement of switchable forces performed on nanoparticles in solution with single beam optical tweezers to date. We compared the results of the force measurement with Mie simulations of the optical scattering force on a gold nanoparticle and found good agreement between experiment and theory within a few fN.

Optomechanical Processing of Silver Colloids: New Generation of Nanoparticle–Polymer Composites with Bactericidal Effect

“…Excited optical force at 248 nm is about 25 pN, which is seven times lower than its maximum at 380 nm. However, with respect to NP size, it is still quite enough to induce collective motion of nanoparticles towards the polymer surface [ 52 , 53 ]. Moreover, the fact that we conducted our experiments at 248 nm, where the absorption cross section is considerably lower than the maximal one, enables us to tailor the surface morphology of polymers by light absorption.…”

Experimental evidence of symmetry breaking of transition-path times

“…In line-shaped traps, the phase-gradient force near the line centre is approximately uniform along the extended direction of the trap. Optical scattering forces lie in the femtoNewton range 55 and are thus of ideal magnitude to bias the Brownian motion of colloidal particles over a few micrometres as sketched in Fig. 2a.…”

Photonic tractor beams: a review

“…Optical tweezers and other related manipulation technologies have become indispensable in various disciplines, including biology, [4][5][6][7] chemistry, 8 quantum science and technology, [9][10][11] and nanotechnology. [12][13][14] One remarkable trend amid this progress is that optical manipulation has been extended, from the initial single freedom of trapping using the conservative optical force, to multiple freedoms using both conservative and nonconservative forces, 15 including pushing, 16 pulling, 17 lateral shifting, rotating, [18][19][20][21] and spinning. 22 Among all the newly developed manipulation freedoms, optical pulling is one of the most interesting and has attracted much attention, [23][24][25][26] due to the potential applications and intriguing physics behind it.…”