Random lasers are principally new sources of stimulated emission where positive feedback realized by multiple light scattering. The laser is active the scattering medium itself without any cavity as well as the other optical elements. Hereupon the lasers distinctions are small gain volume and arbitrary shape.
In this work we investigated lasing parameters of random lasers made of dye polymer solution with embedded scattering particles. The continuous lasing wavelength tuning method was realized in this laser. The method is based on the dye lasing wavelength dependence on the luminescence reabsorption within active medium [1]. Since the reabsorption is dependent on the active region depth it can be continuously changed by wedge-like sample displacing relatively to the focused pump beam.
We realized the continuous lasing wavelength tune within 8nm spectral range in the R6G random laser with silica scattering particles. The active medium was wedge-like shaped of ~0.5cm length with thickness difference Δ d=0.05-0.5mm.
The tune range depends on wedge thickness difference Δ d and light penetration depth into the sample, which could be changed by scattering efficiency varying. The outside tune range is limited by luminescence and absorption spectra overlapping. The accuracy of lasing wavelength tune increases with pump beam cross section σ decreasing. Both lasing threshold and lasing intensity depend on σ and thickness of active medium excited. It is conditioned by two following reasons: effective gain coefficient dependence on the excited region size, and effect of reflection from the sample surfaces on the feedback formation.
[1] E.Tikhonov; Vasil P.Yashchuk, O.Prygodjuk, V.Bezrodny, Yu.Filatov, Functional Materials, v.11,p.142-145,(2003).

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1. Random Laser with Increased Efficiency
2. Vesicular Polymeric Films as High-Efficiency Active Media for the Random Lasers
3. Additional Absorption in the Strongly Scattering Absorbing Media
4. Strongly scattering active media as small-size frequency tunable sources of stimulated emission
5. Multiple scattering use for varying the luminescence spectra of the luminophors
6. Spectral Properties of the Dye Activated Polymers with Added Fine Scattered Particles
7. The Dye Activated Polymers with Added Fine Scattered Particles as New Lasing Media