Trapping microparticles in a structured dark focus

Abstract

We experimentally demonstrate stable trapping and controlled manipulation of silica microspheres in a structured optical beam consisting of a dark focus surrounded by light in all directions -the so-called Dark Focus Tweezer. Results from power spectrum and potential analysis demonstrate the non-harmonicity of the trapping potential landspace, which is reconstructed from experimental data in agreement to Lorentz-Mie numerical simulations. Applications of the dark tweezer in levitated optomechanics and biophysics are discussed.

Levitated Optomechanics: From Gaussian Tweezers to Structured Modes

“…As we also discussed earlier, electromagnetic waves can be shaped into various transverse spatial profiles using the superposition of higher-order modes (Laguerre-Gauss or Hermite-Gauss, for example). With these structured light modes, we can engineer the field gradients, and consequently design novel types of optical traps [37,58]. For instance, we could engineer a stiffer trap, a non-linear trap, and perhaps most interestingly, a multi-particle trap.…”

“…Subsequently, we describe an experimental setup where general structured light optical traps can be implemented. We use this setup to implement a special beam, known in the literature as the optical bottle beam (OBB) [37,38,60].…”

“…Recently, the study of nonlinear optical tweezers has gained prominence [37,39]. By employing beams with complex intensity profiles, like double-well landscapes [35,36], the optical potential experienced by the particle becomes inherently nonlinear, differing from the typical harmonic potential commonly found in optical levitation experiments.…”

“…A second experiment is introduced that addresses the inherent limitations of conventional optical trapping techniques in manipulating particles within complex potential landscapes [35,36]. This segment explores the utilization of structured light in vacuum optical tweezers, employing a Spatial Light Modulator to create an optical bottle beam [37,38], forming a double potential well along the beam's propagation direction. This enables the simultaneous trapping of two particles on the beam's propagation direction, opening avenues for advanced experiments and applications involving controlled inter-particle interactions [39].…”