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Band-edge Liquid Crystal Lasers: Harnessing Photonic Band Gap for Laser Performance

Explore the intricate details of band-edge liquid crystal lasers, unveiling the mechanisms behind their enhanced gain and reduced lasing threshold. Discover how chiral nematic liquid crystals self-organize to create a photonic band gap structure, leading to efficient lasing processes. Dive into the energy level diagrams and optical pumping techniques crucial for optimizing laser performance. Delve deeper into the innovative applications and potential of this cutting-edge laser technology.

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Band-edge Liquid Crystal Lasers: Harnessing Photonic Band Gap for Laser Performance

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  1. Band-edge liquid crystal lasers S.M. Morris, P.J.W. Hands, T.D. Wilkinson, H.J. Coles Centre of Molecular Materials for Photonics and Electronics (CMMPE)Department of Engineering, University of Cambridge Ingredients for a band-edge liquid crystal laser Gain medium Four-level laser dye or light emitter Distributed Feedback Structure Chiral nematic liquid crystal (Right) Absorbance (black) and fluorescence emission (red) spectra for a dye-doped liquid crystal (DCM in E49*). Pumping wavelength chosen to match absorbance peak. Chiral dopant concentration chosen so band-edge matches with fluorescence peak. • Chiral nematic liquid crystals spontaneously self-organize to form periodic dielectric structure – creates photonic band gap (PBG). Macroscopic structure is helical. • Enhanced density of photon states at band-edge of the PBG. (Left) Energy level diagram showing the four-level lasing process in a dye. Cross-over to triplet states and/or excitation to 2nd excited singlet states lead to degradation of performance. • Lasing threshold reduced at band-edge due to increased gain. Optical Pumping (Right) The photonic band gap in a chiral nematic liquid crystal (E49*) (black line), and associated lasing at the long band-edge in a dye-doped chiral nematic cell (DCM in E49*) (red line). (Above & below) Nd:YAG pump focussed into an LC laser cell, generating red laser emission. Further reading:A.D. Ford, S.M. Morris, H.J. Coles, Materials Today, 9 (7-8), pp.36-42, (2006). S.M. Morris, A.D. Ford, C. Gillespie, M.N. Pivnenko, O. Hadeler, H.J. Coles, Journal of the SID, 14 (6): pp.565-573, (2006). V.I. Kopp, Z.-Q. Zhang, A.Z. Genack, Progress in Quantum Electronics, 27, pp.369-416, (2003). www-g.eng.cam.ac.uk/cosmos COSMOS is a Basic Technology Research Grant funded by the EPSRC, EP/D04894X

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