Advanced optical trapping by complex beam shaping

Abstract

Optical tweezers, a simple and robust implementation of optical micromanipulation technologies, have become a standard tool in biological, medical and physics research laboratories. Recently, with the utilization of holographic beam shaping techniques, more sophisticated trapping configurations have been realized to overcome current challenges in applications. Holographically generated higher‐order light modes, for example, can induce highly structured and ordered three‐dimensional optical potential landscapes with promising applications in optically guided assembly, transfer of orbital angular momentum, or acceleration of particles along defined trajectories. The non‐diffracting property of particular light modes enables the optical manipulation in multiple planes or the creation of axially extended particle structures. Alongside with these concepts which rely on direct interaction of the light field with particles, two promising adjacent approaches tackle fundamental limitations by utilizing non‐optical forces which are, however, induced by optical light fields. Optoelectronic tweezers take advantage of dielectrophoretic forces for adaptive and flexible, massively parallel trapping. Photophoretic trapping makes use of thermal forces and by this means is perfectly suited for trapping absorbing particles. Hence the possibility to tailor light fields holographically, combined with the complementary dielectrophoretic and photophoretic trapping provides a holistic approach to the majority of optical micromanipulation scenarios.

Conical refraction: fundamentals and applications

“…They have been extensively used on manipulating colloidal particles, molecules, nanoparticles and even single atoms. Last decade has seen an enormous progress in the field of trapping resulting in the implementation of advanced techniques involving for instance, multiple holographic traps, optical fibers, or singular scalar and vector beams [164,165]. Optimum conditions for particle trapping are dictated by the optical properties of the particles and the surrounding medium, as well as the physical nature of the light-mediated trapping forces.…”

“…That is why hollow (or doughnut) beams are used for efficient trapping in the latter case. In general, depending on the particular media and application, robust trapping and manipulation of micro-objects requires tailoring the light beam intensity pattern via phase and amplitude modulation or by varying the spatial coherence of light [165,[167][168][169].…”

Helicity-dependent three-dimensional optical trapping of chiral microparticles

“…Our proposal for helicity-driven selective 3D optical trapping of transparent chiral particles exploits a twobeam technique allowing to trap microparticles at much longer working distances than those accessible to optical tweezers [1][2][3][4][5][6][7][8][9][10] . This technique has been introduced to capture transparent solid glass microspheres by a pair of counterpropagating moderately focused Gaussian beams 19,20 .…”

“…Three-dimensional (3D) optical trapping of an object implies the use of either bell-shaped (that is, Gaussian) or doughnut-shaped (that is, LaguerreGaussian) light beams depending on (i) the relationship between the refractive indices of the object and its environment, (ii) the relationship between the object size and the beam waist, and (iii) the spatial structure of the light field itself, see the review papers [1][2][3][4] . Noteworthy, neither the spin angular momentum carried by circularly polarized beams nor the orbital angular momentum carried by Laguerre-Gaussian beams are usually considered as basic ingredients for optical trapping.…”

Optical Fiber Tweezers Fabricated by Guided Wave Photo-Polymerization

“…Since the invention of the laser, a vast demand on beam shaping has been verified in areas such as micro-fabrication [1], optical sensing, optical trapping [2,3] of biologic samples or even medicine. Common beam shaping setups include several optical bulk components, which are mostly large and complex [4,5].…”