The birefringence and natural ability to form periodic structures make cholesteric liquidcrystalline (CLC — chiral nematics) materials particularly attractive as 1D photonicband gap systems. If a CLC is doped with dye fluorescent molecules, in such a way thatthe maximum peak of fluorescence matches one of the edges of the selective stop band,laser action is expected at that spectral position. By confining the helical super-structureof chiral liquid crystals in polymeric micro-cavity channels, a tunable microcavity laserarray was achieved. In multiple scattering systems, the propagation of the light wavesis quite different, as optical scattering may induce a phase transition in the photontransport behavior. Beyond a critical scattering level, the system makes a transitioninto a strongly localized state and light transmission is inhibited. This effect can be usedas a photon trapping mechanism to obtain laser action in the presence of a gain medium.Random lasing modes come from interference effects which survive in disordered systemsand open a particular chapter in the study of the interplay between localization andamplification. Here, experiments performed on systems having different order degreeand confinement are presented and possible technological implications are discussed.
Laser action in dye doped liquid crystals: from periodic structures to random media
DE LUCA, Antonio;CAPUTO, Roberto;VERSACE, Consolato Carlo;SCARAMUZZA, Nicola;BARTOLINO, Roberto;UMETON, Cesare Paolo;STRANGI, Giuseppe
2009-01-01
Abstract
The birefringence and natural ability to form periodic structures make cholesteric liquidcrystalline (CLC — chiral nematics) materials particularly attractive as 1D photonicband gap systems. If a CLC is doped with dye fluorescent molecules, in such a way thatthe maximum peak of fluorescence matches one of the edges of the selective stop band,laser action is expected at that spectral position. By confining the helical super-structureof chiral liquid crystals in polymeric micro-cavity channels, a tunable microcavity laserarray was achieved. In multiple scattering systems, the propagation of the light wavesis quite different, as optical scattering may induce a phase transition in the photontransport behavior. Beyond a critical scattering level, the system makes a transitioninto a strongly localized state and light transmission is inhibited. This effect can be usedas a photon trapping mechanism to obtain laser action in the presence of a gain medium.Random lasing modes come from interference effects which survive in disordered systemsand open a particular chapter in the study of the interplay between localization andamplification. Here, experiments performed on systems having different order degreeand confinement are presented and possible technological implications are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.