Optical trapping of nanoparticles by full solid-angle focusing

Abstract

Optical dipole-traps are used in various scientific fields, including classical optics, quantum optics and biophysics. Here, we propose and implement a dipole-trap for nanoparticles that is based on focusing from the full solid angle with a deep parabolic mirror. The key aspect is the generation of a linear-dipole mode which is predicted to provide a tight trapping potential. We demonstrate the trapping of rod-shaped nanoparticles and validate the trapping frequencies to be on the order of the expected ones. The described realization of an optical trap is applicable for various other kinds of solid-state targets. The obtained results demonstrate the feasibility of optical dipole-traps which simultaneously provide high trap stiffness and allow for efficient interaction of light and matter in free space.

Single Photons Emitted by Nanocrystals Optically Trapped in a Deep Parabolic Mirror

“…Such a mirror has been used to study a laser cooled atomic ion held in a radio-frequency trap in vacuum [1]. More recently, the optical trapping of CdSe/CdS dot-inrod particles in a deep PM in air has been demonstrated [2], and lately also the fabrication of a microscopic diamond PM around a nitrogen vacancy centre [3].…”

“…This should occur in a natural way in an optical trap that is built by focusing a radially polarized beam as in Ref. [2]: The electric field in the focus of the PM is purely longitudinal, i.e. parallel to the PM axis.…”

“…The DRs are trapped at ambient conditions in air at the focus of a deep parabolic mirror in an optical dipole-trap (see Ref. [2] and supplementary for details). The electric field at wavelength λ trap = 1064 nm in the focal region is polarized along the optical axis of the PM, which is here defined as the z-direction.…”

“…The fluorescence is detected with a pair of avalanche photo-diodes (APDs). At this stage, fluorescence photons stem from two-photon excitation at λ trap [2]. To determine the intensity auto-correlation function g (2) (t = 0), the power of the trapping laser is reduced such that the count rate of photons on the APDs is hidden in the background noise.…”

“…At this stage, fluorescence photons stem from two-photon excitation at λ trap [2]. To determine the intensity auto-correlation function g (2) (t = 0), the power of the trapping laser is reduced such that the count rate of photons on the APDs is hidden in the background noise. Then, more efficient pulsed excitation at λ exc = 405 nm is switched on and the value of g (2) (t = 0) is measured.…”