ABSTRACT
This work is focused on the structural and morphological investigations of polyaniline and poly(o-anisidine) polymers generated in a direct current glow discharge plasma, in the vapors of the monomers, without a buffer gas, using an oblique angle-positioned substrate configuration. By atomic force microscopy and scanning electron microscopy we identified the formation of worm-like interlinked structures on the surface of the polyaniline layers, the layers being compact in the bulk. The poly(o-anisidine) layers are flat with no kind of structures on their surfaces. By Fourier transform infrared spectroscopy we identified the main IR bands characteristic of polyaniline and poly(o-anisidine), confirming that the polyaniline chemical structure is in the emeraldine form. The IR band from 1070 cm-1 was attributed to the emeraldine salt form of polyaniline as an indication of its doping with Hâº. The appearance of the IR band at 1155 cm-1 also indicates the conducting protonated of polyaniline. The X-ray diffraction revealed the formation of crystalline domains embedded in an amorphous matrix within the polyaniline layers. The interchain separation length of 3.59 Å is also an indicator of the conductive character of the polymers. The X-ray diffraction pattern of poly(o-anisidine) highlights the semi-crystalline nature of the layers. The electrical conductivities of polyaniline and poly(o-anisidine) layers and their dependence with temperature are also investigated.
ABSTRACT
The study of electromagnetic waves propagation in periodically structured dielectrics and the linear and nonlinear optical phenomena in disordered systems doped with gain media represent one of the most challenging and exciting scientific areas of the past decade. Lasing and Random Lasers (RL) are fascinating examples of topics that synergize multiple scattering of light and optical amplification and lately have been the subject of intense theoretical and experimental studies. In this manuscript we demonstrate laser action in a new category of materials, namely dye doped ionic liquids. Ionic liquids prove to be perfect candidates for building, as shown, a series of exotic boundaryless or confined compact laser systems. Lasing is presented in standard wedge cells, freely suspended ionic liquid films and droplets. The optical emission properties are investigated in terms of spectral analysis, below and above lasing energy threshold behavior, emission efficiency, far field spatial laser modes intensity profiling, temporal emission behavior etc. As demonstrated, these materials can be employed as optimal near future replacements of conventional flammable solvents in already available dye laser instruments.
ABSTRACT
An important effect of dynamical localization of light waves in liquid crystal electro-hydrodynamic instabilities is reported by investigating coherent backscattering effects. Recurrent multiple scattering in dynamic and chaotic complex fluids lead to a cone of enhanced backscattered light. The cone width and the related mean free path dependence on the dynamic scattering regimes emphasize the diverse light localization scales related to the internal structures present in the sample. The systems investigated up to now were mainly nano-powdered solutions or biological tissues, without any external control on the disorder. Here, an anisotropic complex fluid is "driven" throughout chaotic regimes by an external electric field, giving rise to dynamics that evolve through several spatio-temporal patterns.
Subject(s)
Liquid Crystals/chemistry , Nephelometry and Turbidimetry/methods , Refractometry/methods , Anisotropy , Computer Simulation , Light , Models, Chemical , Nonlinear Dynamics , Scattering, RadiationABSTRACT
The spatial and temperature dependence of the surface-induced orientational order parameter S(z,T) was determined in the isotropic phase. An optical fiber was immersed in a thin liquid crystal layer and the retardation was measured as a function of the fiber's height above the surface, from which the model-independent S(z,T) was deduced with resolution
ABSTRACT
A statistical analysis of random lasing events observed in dye-doped nematic-liquid-crystal films is reported. The occurrence of random laser action in such complex fluids is due to residual resonances in the multiple scattering of spontaneously emitted photons. The Shannon entropy and a local-Poisson test are used here in order to quantitatively characterize the chaotic behavior of laser spikes and gain further understanding of the mechanisms underlying the lasing effect in strongly scattering organized fluids arising by an unexpected interplay of localization and amplification.
ABSTRACT
Random lasing in fully disordered systems having organic and inorganic nature has been the subject of extensive studies since the beginning of the past decade. The interest mainly emerges from the unexpected role played by disorder in the laser action. The disorder was considered detrimental for the optical feedback in cavity laser, until it was demonstrated that multiple-scattering materials including a gain medium act as random laser. Here, a completely new approach is reported, where freely suspended complex fluid films doped with fluorescent molecules under optical excitation generate narrowband lasing peaks. The constellation of localized modes is selected by properly choosing the gain profile. The idea to have laser action in absence of mirrors and boundaries realizes an unparalleled tunable and moldable laser source.
ABSTRACT
An anisotropic nanopatterning method, based on a technique of atomic force microscopy (AFM) scribing of a thin polyimide film, is used to generate an alignment layer whose topography depends on the writing direction. Detailed experimental measurements are presented for the topographical anisotropy that arises when the polyimide alignment layer is scribed parallel and antiparallel to the AFM cantilever orientation. By means of a novel nanotomographic approach, the optical retardation δ of an alignable birefringent liquid that covers the scribed substrate is measured with unprecedented resolution of only a few tens of nanometers. In this technique a thin optical fiber is raster-scanned at several fixed heights inside the birefringent liquid, and the transmitted polarized light is collected downstream. The optical retardation δ from the fiber's tip to the polyimide interface was measured as a function of position x,y,z, with the results reflecting the spatially varying depth of the medium due to the polymer film surface topography. Theoretical calculations for δ are in excellent agreement with both the topographical and the high resolution nanoimaging experimental results obtained.
ABSTRACT
We report a detailed physical characterization of a novel array of organic distributed feedback microcavity lasers possessing a high ratio between the quality factor Q of the resonant cavity and its volume V. The optical microcavity was obtained by confining self-organized mesophases doped with fluorescent guest molecules into holographically patterned polymeric microchannels. The liquid crystal microchannels act as mirror-less cavity lasers, where the emitted laser light propagates along the liquid crystal helical axis behaving as Bragg resonator. This miniaturization process allows us to obtain a micro-laser array possessing an ultralow lasing threshold (25nJ/pulse) while having directional control on the lasing emission, a fine wavelength tunability and the control over the emission intensity.
ABSTRACT
Distributed feedback microstructures play a fundamental role in confining and manipulating light to obtain lasing in media with gain. Here, we present an innovative array of organic, color-tunable microlasers which are intrinsically phase locked. Dye-doped helixed liquid crystals were embedded within periodic, polymeric microchannels sculptured by light through a single-step process. The helical superstructure was oriented along the microchannels; the lasing was observed along the same direction at the red edge of the stop band. Several physical and technological advantages arise from this engineered heterostructure: a high quality factor of the cavity, ultralow lasing threshold, and thermal and electric control of the lasing wavelength and emission intensity. This level of integration of guest-host systems, embedded in artificially patterned small sized structures, might lead to new photonic chip architectures.
