A new kind of optical microresonators from droplets of nematic liquid crystal were made. The light is trapped inside these spheres and »circulates« close to the surface. Instead of using isotropic solid state spheres, we used nematic drops, since their refraction index can be changed with the external electric field. Observations were in excellent agreement with our numerical simulations. By applying electric field we have achieved tuning range almost hundred times larger than in solid microresonators. This enables their application for tunable lasers, active filters and optical switches. In a cholesteric liquid crystal droplet with a concentric layered structure that enables internal Bragg reflection a stimulated laser light emission was realized. The droplet that behaves as a point source of laser light is in a fact a first 3D microlaser. (HUMAR, Matjaž, MUŠEVIČ, Igor, 3D microlasers from selfassembled cholesteric liquidcrystal microdroplets. Optics Express 2010, vol. 18, 2699527003 [COBISS.SIID 24377895]). The discovery is protected by a patent application [COBISS.SIID 25561639].
COBISS.SI-ID: 22940455
In this work, knotting of defect lines in liquid crystal colloids, confined to thin twisted nematic cells, is presented. Defect are manipulated with optical tweezers to form arbitrary knots or links that entangle the colloidal particles into twodimensional crystals. Knots of arbitrary complexity can be systematically designed, with all knots with up to 6 crossings presented in the paper, including the Hopf link, Borromean rings and Solomon link. Complexity of presented structures is beyond the complexity of knots ever seen before in soft matter and reinforces importance o topology in material science. Our achievements in fact established a new research field “topological soft matter” that attracted a lot of attention. The publication of the paper in the journal “Science” was accompanied by a commentary of R. Kamien from UPenn who is the key expert for topology of liquid crystals. The discovery also stimulated the realization of one month mini program on “Knotted fields” at KITP UC Santa Barbara, where we as the authors of the paper, playe a notable role (http://online.kitp.ucsb.edu/online/knotsm12/). The publication in Science was also met with a formal commendation by President of Slovenia dr. Danilo Türk, who on the occasion also visited the involved research groups lead by prof. Slobodan Žumer and prof. Igor Muševič
COBISS.SI-ID: 2336868
First 3D nematic dipolar colloidal crystal was presented, which is a new milestone in the field of assembling nematic colloids. It was predicted by Landau - de Gennes analysis of stability colloidal crystal structures, assembled with the help of laser tweezers and studied by 3D confocal polarization fluorescent microscopy. Dipolar colloidal crystal has tetragonal symmetry and exhibit giant electrostriction. An external electric field induces a reversible and controllable electrorotation of the crystal as a whole, when using LC with negative dielectric anisotropy. The study opens the field of assembling 3D colloidal crystals in the nematic media. These structures offer new possibilities for photonic applications.
COBISS.SI-ID: 26543143
This review article written on invitation summarizes knowledge about topology of disclinations in nematic liquid crystals. Previously known theory is followed by a large portion of the article that is based on the author's work of the last few years partially in collaboration with other members of the program (PRL 2011, PRE2012, Proc. R. Soc. A 2013, PRE 2013, PRL 2013, Soft Matter 2013). The theory is a well-rounded whole that treats geometric and topological description of defect loops, specifically focused on nematic colloids.
COBISS.SI-ID: 2636388
The research was performed in tight collaboration of our group for modeling and simulations with the group of Professor I. Smalyukh from Boulder where colloids were actually made and experimentally studied. The paper reports on mutual knitting of knots in the shape of micro-particles and knots in the molecular field of nematic liquid crystals. The particle-knots are produced by laser two-photon photopolymerization. Numerical modelling is used to explore the structure of the nematic fields, which reveals an interesting mutually tangled topology of particle- and field-knots. The demonstrated approach may find uses in self-assembled topological superstructures and as topological scaffolds. The paper was distinguished by the front cover of Nature Materials and with an accompanying News&Views paper.
COBISS.SI-ID: 2630244