Multiple Scattering Active Media as Small-Size Frequency Tunable Sources of Stimulated Emission

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.

Nonresonant feedback formation in the random laser

“…In the plane samples the transverse sizes exceed sample thickness, thus only two sample surfaces, i.e. front (relatively to incident pump beam) and back (opposite to one), take part in the feedback formation [4]. The reflection feedback is formed due to reflection both by the boundary particles and at the polymerair surface.…”

“…There are two types of feedback in random laser: resonant and nonresonant [3]. According to the preliminary investigations [4] the boundary conditions significantly influence the nonresonant feedback formation. This paper is devoted to investigation of this problem.…”

Improvement of the random laser efficiency

“…This spectrum thinning and the threshold decreasing testify that the feedback efficiency is higher in thin samples. According to [2] random lasing is caused by two types of positive feedback. The first type is the feedback due to light scattering on the particles in the sample volume; the second one is formed owing to reflection from the sample surface.…”