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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 18:03 |
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Conference: Bucharest University Faculty of Physics 2017 Meeting
Section: Polymer Physics
Title:
Special features of nematic dye-doped lasers
Authors:
Valentin BARNA
Affiliation:
University of Bucharest, Faculty of Physics, PO Box MG 11, Magurele-Bucharest, Romania
E-mail
barnavalentin@yahoo.com
Keywords:
patio-temporal emission pattern, coherent backscattering, nematic liquid crystals, nematic-isotropic phase transition, micro-droplets nucleation
Abstract:
Experimental investigations of random laser action in a partially ordered, dye doped nematic liquid crystals with long-range dielectric tensor fluctuations are reported. Above a given pump energy value, a randomly distributed series of bright tiny spots appear, giving rise to a strongly fluctuating spatio-temporal emission pattern (spectral peak ca. 0.5 nm FWHM). The unexpected surviving of interference effects in recurrent multiple scattering of the emitted photons provide the required optical feedback for lasing in nematics. Coherent backscattering of light waves in orientationally ordered nematic liquid crystals manifests a weak localization of light which strongly supports diffusive laser action in presence of gain medium. Unlike distributed feedback mirror-less lasers, this system can be considered as a cavity-less microlaser where the disorder unexpectedly plays the most important role, behaving as randomly distributed feedback laser. Important experimental evidence reveal a strong temperature dependence of the random lasing characteristics in the nematic phase and in close proximity of the nematic-isotropic (N-I) phase transition. The optical losses increase, owing to the thermal fluctuation enhanced scattering, and drive the input-output smoother behavior until the system stops to lase, because situated below threshold. The unexpected reoccurrence of random lasing at higher temperatures, in proximity of N-I transition is found to be related to a different scattering mechanism, the micro-droplets nucleation.
Acknowledgement:
The research activities were supported from the RO PN-II-RU-TE-2014-2412 grant.
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