We demonstrate that Direct Laser Writing (DLW) can be used to print low loss planar polymer waveguides on glass, thus promising a novel soft matter platform for polymer all-optic micro-photonics. We printed straight waveguides with various cross sections and lengths up to 900μm on a 500nm thin layer of low refractive index CYTOP on glass. We also printed two rectangular micro-prisms at each end of the waveguide, which provides coupling of light in and out of the waveguides. The printed structures were imaged and characterized by SEM and we measured the attenuation of light, propagating along the waveguides. While the high refractive index photosensitive resin IP-n162 shows moderate attenuation of ∼14dB/cm at 580nm, the IP-S photosensitive resin shows lower attenuation of ∼5-9dB/cm in a rather broad window around 580nm.
The interactions between different types of colloidal particles are measured and analyzed. We use these interactions to
build different self-assembled microstructures, such as dimers, chains, wires, crystals and superstructures. In the
experiments we have used different size, different symmetry of colloids (elastic dipoles and quadrupoles) and different
way of colloidal binding (via localized defects and via entangled defects). We use optical tweezers for directed selfassembly
of colloidal particles. Special attention is devoted to the hierarchical superstructures of large and small
particles. We show that smaller, submicron colloidal particles are trapped into the topological defect rings or loops,
twisting around larger colloidal particles, which are sources of strong nematic deformations. Various possible
applications are discussed, especially in photonics and metamaterials.
We describe and analyze experiments, where optical manipulation of small colloidal particles in the nematic liquid
crystal (NLC) was used to create artificial colloidal structures, such as 1D chains and 2D colloidal crystals, and
superstructures of different types of colloids. In all cases, the colloidal particles are strongly bound to each other, with a
typical pair interaction energy of several 1000 kBT per 1μm size particle. There are two distinct mechanisms of colloidal
binding in a spatially homogeneous NLC: (i) binding via spatially localized topological (point) defects, and (ii) binding
via entangled topological defects, where the defect line winds around and wraps several colloidal particles.
We describe and analyze laser trapping of small colloidal particles in a nematic liquid crystal, where the index of refraction of colloidal particles is smaller compared to the indices of the liquid crystal. Two mechanisms are identified that are responsible for this anomalous trapping: (i) below the optical Freedericksz transition, the trapping is due to the anisotropic dielectric interaction of the polarized light with the inhomogeneous director field around the colloidal particle, (ii) above the optical Freedericksz transition, the optical trapping is accompanied by the elasticity-mediated interaction between the optically distorted region of a liquid crystal and the particle. In majority of the experiments, the trapping above the Freedericksz transition is highly anisotropic. Qualitative agreement is found with a numerical analysis, considering nematic director elastic distortion, dielectric director-light field coupling and optical repulsion due to low refraction index colloid in a high index surroundings.
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