Interference of the scattered vector light fields from two optically levitated nanoparticles

Abstract

We experimentally study the interference of dipole scattered light from two optically levitated nanoparticles in vacuum, which present an environment free of particle-substrate interactions. We illuminate the two trapped nanoparticles with a linearly polarized probe beam orthogonal to the propagation of the trapping laser beams. The scattered light from the nanoparticles are collected by a high numerical aperture (NA) objective lens and imaged. The interference fringes from the scattered vector light for the different dipole orientations in image and Fourier space are observed. Especially, the interference fringes of two scattered light fields with polarization vortex show the π shift of the interference fringes between inside and outside the center region of the two nanoparticles in the image space. As far as we know, this is the first experimental observation of the interference of scattered vector light fields from two dipoles in free space. This work also provides a simple and direct method to determine the spatial scales between optically levitated nanoparticles by the interference fringes.

On the free rotation of a polarized spinning-top as a test of the correct radiation reaction torque

“…For the cubic DAST-nanocrystal of the dimension a = 100 nm with equal inertia moments I = 2.3 • 10 −26 g•cm 2 and the dipole moment d = 5.6 • 10 7 D we have the time scale τ 0 = 3.4 • 10 −27 c. Thus, if the initial angular velocity Ω 30 ∼ Ω 20 ∼ Ω 0 ∼ π • 10 10 Hz, as in the experiment [2], the characteristic braking time Θ ∼ 1/(τ 0 Ω 2 0 ) ∼ 4 days which is of order of a storage time in Penning trap [15]. Then such a nanocrystal might serve as a test for choosing between the reduced Euler equation, and the truncated one, that is between the balance equations (2.1) and (2.4a).…”

“…A better experimental test to distinguish between two aforementioned frameworks might be a cubic DAST-nanocrystal of size, say a = 100 nm, possessing, in theory [12], the giant dipole moment d = 5.6 • 10 7 D . We suppose that it can be spun up to the initial angular velocity Ω 0 = π • 10 10 Hz, as in the experiment [2]. Then such a nanocrystal could serve as a test for choosing between balance equations (2.1) and (2.4a).…”

“…Nowadays, nanoparticles in optical traps can be spun up to GHz [1,2]. On the other hand, the dipole moment of some artificially created nanoparticles, such as inorganic nanocrystals CdSe and CdS [3] or cellulose nanocrystals [4] reaches hundreds and thousands Debyes.…”

On-demand assembly of optically-levitated nanoparticle arrays in vacuum

“…The scattering light is collected by the same high NA objective to form an image on a charge-coupled device (CCD). This configuration provides a dark background and a high signal-noise ratio for imaging levitated nanoparticles [37,38]. The scattering 532 nm light intensity shown in the image provides preliminary information about the size of each trapped nanoparticle.…”