Imaging the dipole scattering of an optically levitated dielectric nanoparticle

Abstract

We experimentally observe the dipole scattering of a nanoparticle using a high numerical aperture (NA) imaging system. The optically levitated nanoparticle provides an environment free of a particle–substrate interaction. We illuminate the silica nanoparticle in vacuum with a 532 nm laser beam orthogonally to the propagation direction of the 1064 nm trapping laser beam strongly focused by the same high NA objective used to collect the scattering, which results in a dark background and high signal-noise ratio. The dipole orientations of the nanoparticle induced by the linear polarization of the incident laser are studied by measuring the scattering light distribution in the image and the Fourier space (k-space) as we rotate the illuminating light polarization. The polarization vortex (vector beam) is observed for the special case, when the dipole orientation of the nanoparticle is aligned along the optical axis of the microscope objective. Our work offers an important platform for studying the scattering anisotropy with Kerker conditions.

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

“…Simultaneously, the polarization in the image and Fourier space is linear, aligned along x-axis. Case 3 for the arbitrary polarization of the illuminating light is discussed in our previous work [35]. The dark area in the image and Fourier space will appear on the right and gradually move towards the center when the polarization of the illuminating light rotates from −π/2 to 0 (Figs.…”

“…Similarly, the k-vector of the scattered field is denoted by (θ, ϕ). The intensity distribution in the backaperture plane of the objective lens, which is the Fourier space (kspace) distribution of the scattered light, can be written as [35,49]…”

“…In this system, the micro-and nano-particles are free from particle-substrate compared to other systems which have particle-environment interactions [30][31][32][33][34]. Recently our group reported the imaging of the dipole scattering orientations of an optically levitated silica nanoparticle in the image and Fourier space (k-space) [35]. This system has several distinguished features.…”

Isolating noise and amplifying signal with quantum Cheshire cat

“…A significant concern in experiments is the minimizing noise in the relevant signal and designing measurement techniques that achieve the same. A measurement strategy with a greater signal to noise ratio is typically favored by experimentalists [28][29][30][31][32][33], apart from logistics and dependencies on other constraints imposed by the particular scenario. We consider a situation in which noise may be introduced during the process of weak value amplification if the Hamiltonian in Eq.…”

Optical trapping core formation and general trapping mechanism in single-beam optical tweezers

“…A milestone in optical micromanipulation is the stable optical trapping of nanoparticles by single-beam optical tweezers [18][19][20][21][22][23]. In general, the optical trapping of small Rayleigh particles [24][25][26] and large particles in the context of the geometrical optics limit [27] has been examined based on the decomposition of the optical force into two components, namely, conservative and nonconservative forces.…”