Liquid crystalline chromophores for photonic band-edge laser devices

• Published in: Optical materials Vol. 35; no. 5; pp. 837 - 842
• Main Authors: Morris, Stephen M., Qasim, Malik M., Gardiner, Damian J., Hands, Philip J.W., Castles, Flynn, Tu, Gouli, Huck, Wilhelm T.S., Friend, Richard H., Coles, Harry J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01.03.2013; Elsevier
• Subjects: Chromophores; Dyes; Emission; Exact sciences and technology; Excitation spectra; Fundamental areas of phenomenology (including applications); Laser materials; Lasers; Liquid crystals; Molecular structure; Optical materials; Optics; Phases; Physics; Lasers; Liquid crystals; Dyes; Band structure; Organic lasers; Organic dye; Molecular structure; Laser materials; Chromophores; Optical materials; Nematic crystals
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2012.10.046

► Liquid crystalline chromophores have been synthesized for photonic band-edge laser devices. ► These are bimesogenic compounds consisting of the repeating unit from the semiconducting polymer, CNPPV. ► Single mode laser emission was observed in chiral nematic samples doped with the chromophores up to a concentration of 10wt.%. ► The excitation threshold is found to increase with the concentration of the chromophore. We present results on laser action from liquid crystal compounds whereby one sub-unit of the molecular structure consists of the cyano-substituted chromophore, {phenylene-bis (2-cyanopropene)}, similar to the basic unit of the semiconducting polymer structure poly(cyanoterephthalylidene). These compounds were found to exhibit nematic liquid crystal phases. In addition, by virtue of the liquid crystalline properties, the compounds were found to be highly miscible in wide temperature range commercial nematogen mixtures. When optically excited at λ=355nm, laser emission was observed in the blue/green region of the visible spectrum (480–530nm) and at larger concentrations by weight than is achievable using conventional laser dyes. Upon increasing the concentration of dye from 2 to 5wt.% the threshold was found to increase from Eth=0.42±0.02μJ/pulse (≈20mJ/cm2) to Eth=0.66±0.03μJ/pulse (≈34mJ/cm2). Laser emission was also observed at concentrations of 10wt.% but was less stable than that observed for lower concentrations of the chromophore.