Liquid Crystal Lasers_ Recent Advances.pdf

Liquid Crystal Lasers: Recent Advances Juergen Schmidtke*a, Lu Lua, Heinz-S. Kitzerowa, Eugene M. Terentjevb aFaculty of Science, Univ. of Paderborn, Warburger Str. 100, 33098 Paderborn bCavendish Laboratory, Univ. of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK ABSTRACT During the past decade, photonic band edge lasers based on cholesteric liquid crystals (CLCs) have attracted considerable interest as self-assembled coherent, tunable lights sources. We report on recent progress towards practical applications: (i) Electrical fine tuning of laser emission by in-plane electric fields: the field-induced distortion of the cholesteric helix allows for a controllable, continuous and reversible shift of the band edge resonances. (ii) Improvement of lasing performance by application of an electric field along the helical axis of a system with negative dielectric anisotropy: the electric field stabilizes the soft photonic structure against heating-induced distortions. (iii) PDMS- enclosed LC lasers for lab-on-a-chip applications: We demonstrate the formation of a uniform planar cholesteric texture between polydimethylsiloxane (PDMS) substrates and narrow-band laser emission of a PDMS-enclosed LC laser. With PDMS being the standard material for the fabrication of microfluidic devices, this opens a simple and flexible route for the integration of coherent light sources in lab-on-a-chip designs. Keywords: DFB lasers; dye lasers; tunable lasers; liquid crystals; lab on a chip 1. INTRODUCTION Cholesteric liquid crystals (CLCs, a.k.a. chiral nematic liquid crystals) are soft, self-assembled photonic materials. They consist of rod-like molecules, which locally have a nematic order; addition of a chiral compound results in a continuous twist of the director field. Due the continuous rotation of the dielectric tensor along a certain axis, a CLC acts as a one dimensional, polarization-sensitive photonic crystal: It shows a photonic stop band for ci