Abstract
Stable optical trapping and manipulation of high-index particles in low-index host media is often impossible due to the dominance of scattering forces over gradient forces. Here we explore optical manipulation in liquid crystalline structured hosts and show that robust optical manipulation of high-index particles, such as GaN nanowires, is enabled by laser-induced distortions in long-range molecular alignment, via coupling of translational and rotational motions due to helicoidal molecular arrangement, or due to elastic repulsive interactions with confining substrates. Anisotropy of the viscoelastic liquid crystal medium and particle shape give rise to a number of robust unconventional trapping capabilities, which we use to characterize defect structures and study rheological properties of various thermotropic liquid crystals.
Highlights
Optical trapping is a non-contact manipulation technique broadly used in science fields ranging from condensed matter physics to biology and biomedicine, as well as for various technological applications [1,2,3]
Stable manipulation typically uses tightly focused laser beams that exert optical gradient forces and pull particles towards the maximum-intensity region of the focal plane and overcome scattering forces that tend to push the particle along the light-propagation direction [4]
We explore optical manipulation of high-index GaN nanowires infused in nematic and cholesteric liquid crystals (LCs) in the regime when optical gradient forces are much weaker than scattering forces
Summary
Optical trapping is a non-contact manipulation technique broadly used in science fields ranging from condensed matter physics to biology and biomedicine, as well as for various technological applications [1,2,3]. Stable manipulation typically uses tightly focused laser beams that exert optical gradient forces and pull particles towards the maximum-intensity region of the focal plane and overcome scattering forces that tend to push the particle along the light-propagation direction [4]. This imposes restrictions on the refractive indices of the particles with respect to the fluid host media, that the refractive index of particles has to be modestly higher than that of the medium. This robust structure-assisted trapping allows us to characterize three-dimensional (3D) defect morphology and local rheological properties of LCs
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