Random lasers are a novel disorder-based laser light source with many photonics applications. In the present work we study the optical properties of a new unordered medium consisted of an epoxy resin as matrix with dissolved different binary solutions of Rhodamine 6G and Rhodamine B. The choice of these dyes is related to their great application in laser physics. A detailed study of the spectral dependence of fluorescence is performed. The spontaneous emission is very intensive and follows the spectral dependence of dyes transmission and exceeds 750 nm. The threshold of the laser medium is 1.6 mJ for 10 ns pulse at second harmonics of Nd:YAG laser, and full width at half maximum (FWHM) is around 1.5 nm. Slope efficiency of the medium is 16%. The laser generation without resonator was studied also and lasing emission at 597 nm was observed. The fact can be explained by random lasing provided by the medium. This is in good relation and in accordance with the intensive scattering inherent to the medium which is registered. Not used additional scatter centers such as ZnO nanorods or Ag, Al, Al2O3, TiO2 agglomerates and others in our experiments.
Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like (multi-layered graphene, graphene oxide etc.), graphite flakes etc. as fine suspensions were obtained by pulsed laser ablation of highly purified microcrystalline graphite targets immersed in double distilled water. The fundamental wavelength (λ = 1064 nm) and the fourth harmonic (λFHG = 266 nm) of a Nd:YAG laser system (15 ns pulse duration, 10 Hz pulse repetition rate) were used in the fabrication process. The laser fluence value corresponding to the onset of the ablation process, the one initiating optical breakdown in water and an intermediate value were used for each of the wavelengths mentioned above. The morphology of the particles dispersed in water was studied by scanning electron microscopy (SEM). Their phase composition and structure were explored by Raman spectroscopy. It showed the presence of some traces of polymerized hydrocarbons (polystyrene, polybutadiene etc.) in addition to the main carbon phases: defected graphene, reduced graphene oxide and graphite.
In the current study triblock copolymers (Pluronics) consisting of central poly(propylene oxide) (PPO) block flanked by two poly(ethylene oxide) (PEO) chains are used as organic templates for generating mesoporosity in thin Nb2O5 films. In order to optimize the polymer framework within the Nb2O5 films, two copolymers with different chemical compositions and properties are used, namely Pluronic PE 6200 and PE 9400. The copolymers’ micelle formation is studied by Dynamic Light Scattering (DLS) measurements of the copolymer aqueous solutions at different temperatures and concentrations and by Transmission Electron Microscopy (TEM). Thin films of mesoporous Nb2O5 films are deposited by sol-gel and spin-coating methods and characterized by TEM, UV-VIS reflectance spectroscopy and non-linear fitting for optical properties determination. The porosity of the films is calculated using effective medium approach on the basis of dispersion curves of the calculated refractive indices. The development of porosity in the films is studied as a function of the duration of the annealing. Besides, the sensing properties of mesostructured films are tested with vapors of acetone as a probe molecule of VOC’s (Volatile Organic Compounds) by reflectance measurements prior to and after exposure to vapors. The films optical response is demonstrated and possible application as optical indicator for VOC’s is discussed.
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