Manipulation of colloidal gold nanoparticles in the evanescent field of a channel waveguide

Abstract

Colloidal gold spheres of radius 10 nm are reported to move forward in water, under the influence of radiation pressure forces, due to the evanescent field at the surface of an optical channel waveguide. The velocity is linearly dependent upon the optical power in the waveguide, acquiring a maximum velocity of 4 μm/s for modal power of 500 mW in the TM polarization at a wavelength of λ=1.047 μm.

Velocity distribution of Gold nanoparticles trapped on an optical waveguide

“…Here we use the lower value as it is the most often cited value. The agreement between theory and experiment (speeds up to 384µm/s predicted, with speeds of 500µm/s observed) is much improved on previous calculations [4].…”

“…In order to compare this to theory we equate the Rayleigh optical forces to the Stokes' drag forces to predict the velocity [4]. The peak intensity in the evanescent field of the waveguide was estimated to be 9GW m −2 per Watt of propagating modal power, using beam propagation analysis (RSoft), for which the refractive index distribution was taken from slab waveguides formed under the same conditions, and knowledge of the waveguide diffusion width.…”

“…Kawata and Tani first demonstrated the propulsion of 0.5µm gold and 1µm platinum particles on waveguides [3]. More recently, Ng showed that 40nm gold particles could also be propelled and demonstrated the effects of polarization, waveguide width and modal power on the speed of particles [3,4]. The trapping and propulsion of latex particles of diameter 1µm or above, where the effects of Brownian motion are much smaller, have also been studied on a waveguide [1-3, 6, 7] and above a prism [10,11].…”

“…The optical propulsion of gold or dielectric particles on an optical waveguide has been reported by several groups [1][2][3][4][5][6][7], with proposed applications in sorting of biological species [1,7,8] and in chemical sensing by surface enhanced Raman spectroscopy [9]. Kawata and Tani first demonstrated the propulsion of 0.5µm gold and 1µm platinum particles on waveguides [3].…”

Extraordinary momentum and spin in evanescent waves

“…Figure 3a,c shows the schematic of the corresponding experiment using the total internal reflection at a glass prism. For this numerical experiment, we use parameters corresponding to real experiments manipulating particles with evanescent fields (for example see refs [57][58][59][60][61][62]. Namely, we consider radiation with the wavelength l ¼ 650 nm, a gold particle (e p ¼ À 12.2 þ 3i, m p ¼ 1) in water (e ¼ 1.77, m ¼ 1), and near-critical total internal reflection (the angle of incidence is y ¼ 51°¼ y c þ 1.5°) from the interface between heavy flint glass (e 1 ¼ 3.06, m 1 ¼ 1) and water.…”