Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical Trapping in a Dark Focus
134
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The superposition of a Gaussian mode and a Laguerre-Gauss mode with $ell=0,p eq0$ generates the so-called bottle beam: a dark focus surrounded by a bright region. In this paper, we theoretically explore the use of bottle beams as an optical trap for dielectric spheres with a refractive index smaller than that of their surrounding medium. The forces acting on a small particle are derived within the dipole approximation and used to simulate the Brownian motion of the particle in the trap. The intermediate regime of particle size is studied numerically and it is found that stable trapping of larger dielectric particles is also possible. Based on the results of the intermediate regime analysis, an experiment aimed at trapping living organisms in the dark focus of a bottle beam is proposed.
rate research
Read More
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.
Standard optical tweezers rely on optical forces that arise when a focused laser beam interacts with a microscopic particle: scattering forces, which push the particle along the beam direction, and gradient forces, which attract it towards the high-intensity focal spot. Importantly, the incoming laser beam is not affected by the particle position because the particle is emph{outside} the laser cavity. Here, we demonstrate that emph{intracavity nonlinear feedback forces} emerge when the particle is placed emph{inside} the optical cavity, resulting in orders-of-magnitude higher confinement along the three axes per unit laser intensity on the sample. We present a toy model that intuitively explains how the microparticle position and the laser power become nonlinearly coupled: The loss of the laser cavity depends on the particle position due to scattering, so the laser intensity grows whenever the particle tries to escape. This scheme allows trapping at very low numerical apertures and reduces the laser intensity to which the particle is exposed by two orders of magnitude compared to a standard 3D optical tweezers. We experimentally realize this concept by optically trapping microscopic polystyrene and silica particles inside the ring cavity of a fiber laser. These results are highly relevant for many applications requiring manipulation of samples that are subject to photodamage, such as in biological systems and nanosciences.
We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of the optical torque. We find overall agreement with theory, with no fitting, provided that astigmatism, which is characterized separately, is included in the theoretical description. Our work opens the way for characterization of the trapping parameters, such as the microsphere complex refractive index and the astigmatism of the optical system, from measurements of the microsphere rotation angle.
Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer. In the case of 3D trapping with a single beam, this is termed optical tweezers. Optical tweezers are a powerful and non-invasive tool for manipulating small objects, which have become indispensable in many fields, including physics, biology, soft condensed matter, amongst others. In the early days, optical trapping were typically used with a single Gaussian beam. In recent years, we have witnessed the rapid progress in the use of structured light beams with customized phase, amplitude and polarization in optical trapping. Unusual beam properties, such as phase singularities on-axis, propagation invariant nature, have opened up novel capabilities to the study of micromanipulation in liquid, air and vacuum. In this review, we summarize the recent advances in the field of optical trapping using structured light beams.
We theoretically investigate the influence of a longitudinal laser polarization component from beam focussing on spin dynamics in Kapitza-Dirac scattering by solving the relativistic Dirac equation with time-dependent perturbation theory. The transverse spacial dependence of the longitudinal beam polarization component is accounted for, by approximating a Gaussian beam with plane-wave components. We find that corrections from a longitudinal laser beam polarization component approximately scale with the second power of the diffraction angle $epsilon$, from which we conclude that a related influence from beam focussing can be made negligibly small for sufficiently low beam foci.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
