Embed Size (px)
Citation preview
Quenching nematicon fluctuations via photo-stabilization
N. Karimi, A. Alberucci, M. Virkki, A. Priimägi, M. Kauranen and G. Assanto
Faculty of Natural Science, Tampere University of Technology, P.O. Box 692, FI-33101Tampere, Finlandemail: [email protected]
Nematic liquid crystals (NLC) have attracted tremendous interest as nonlocal media forlight-induced waveguides through their significant nonlinear response based on reorien-tation. Self-guided beams in NLC (Nematicons[1]) are subject to noninstantaneous dy-namics and instabilities resulting in trajectory fluctuations in time, particularly at highexcitations. In an effort to reduce such fluctuations, various routes have been explored,including the use of longitudinal electric fields [2] and of lower temperatures. Here wedemonstrate a decrease in nematicon transverse fluctuations through photo-induced stabi-lization. Nematicons were generated by launching a 3 mW continuous-wave laser beam(λ=1064 nm) into a 3 mm long and 100 µm thick planar cell filled with 5CB doped with10 mol-% monoacrylate (Fig.1.a). Simultaneously, we illuminated the NLC with a UVlamp (λ=365 nm, power density 5 mW/cm2), and monitored the soliton trajectories ver-sus the exposure time. Fig.1.b clearly indicates a substantial decrease in the angular spanof nematicon fluctuations with increasing UV exposure. Each panel shows a fan of soli-ton paths in the propagation plane yz, as obtained by acquiring several images of beamevolution in a time window of about 4.5 s fora fixed beam power. The envelope of the soli-tary paths resulted in a cone of aperture decreas-ing versus progressive UV illumination, its sizenearly halving after 120 min (Fig.1.b, right) ascompared to the case without exposure (Fig.1.b,left). This new NLC system exhibits lowertransverse instabilities without penalty on thenonlinear response. Such improved response,consistent with previous reports in polymer sta-bilized liquid crystals [3], can be attributed tohigher viscosity through the partial formationof a polymer network, even though neither di-acrylates nor photo-initiators were introduced.These results are promising towards the all-optical realization of robust and temporally sta-tionary guided-wave structures for optical sig-nal processing.
Fig. 1. (a) Intensity evolution of a 3mW extraordinary-polarized beam inthe NLC. (b) Nematicon trajectories inthe yz plane, (left) before UV illumina-tion, (middle) after 90 min and (right)after 120 min, respectively.
[1] M. Peccianti and G. Assanto, Phys. Rep. 516, 147 – 208 (2012).[2] J. F. Henninot, J. F. Blach and M. Warenghem, J. Opt. A: Pure Appl. Opt. 10, 085104
(2008).[3] J. F. Blach, et al. J. Opt. Soc. Am. B 5, 1122–1129 (2007).
