Papers by Author: Vasil P. Yashchuk

Abstract: Numeric simulation of light passing through the scattering medium by the Monte-Carlo method was carried out. The influence of multiple scattering on the light beam attenuation in an absorbing media was investigated. The additional absorption appearance was shown to be initiated by multiple scattering. The experimental evidence for this absorption is abrupt increasing of beam attenuation at high particle concentrations. The behaviour of the additional absorption was investigated. The results of numeric calculation are in good agreement with experimental results.

Abstract: Continuously tunable random laser basing on rhodamine 6G was achieved. Wavelength tuning was implemented by wedge-shaped sample shift relatively to the pump beam. The physical base of the tuning method is gain band shift caused by reabsorption. We ascertained that two medium thickness ranges of significantly different tune efficiency exist. The lasing characteristics of the laser were investigated depending on active medium and pump beam parameters. The feedback formation mechanisms in the random lasers of different thickness were analyzed.

Abstract: The behaviour of the luminescence spectra of the organic dye R6G in a multiple scattering polymer matrix was studied with reference to the parameters of the scattering media. It was found that some of the luminescent parameters depend on the concentration of scattering particles, the refractive index of the scattering particles and the sample thickness. As it was shown, that the reason for these dependences is the reabsorption of luminescence light enhanced by multiple light scattering. In addition, an increase in the absorption caused by multiple scattering was observed.

Abstract: We investigated the lasing spectra of multiple scattering active media based on solid polymer solutions of rhodamin 6G with embedded scattering silica particles of mean diameter 500nm. Lasing in these samples appears without any cavity and arises even in rather small active volume 0.05*0.5*0.5mm3. In a thick sample positive feedback for lasing is provided mainly by multiple scattering of light. In a thin sample the feedback is provided both by multiple scattering of light on the particles and light reflection from the sample surface. It is found that the lasing spectra peak wavelength can be varied within 13nm by varying sample thickness in a range 0.1 -1.65mm. A method of continuos laser tuning by wedge-like sample shift with respect to the pump beam is proposed. The presented results are aimed at the development of a new type of microlaser.