Abstract

Lasing action in random amplifying media^1,2 has been observed in powdered phosphors³ and in colloidal suspension in dye solution.⁴ The radiation following pulsed excitation is emitted in a short burst with a narrowed spectrum as compared with spontaneously emitted radiation above threshold.^4-6 Because stimulated emission may be induced at a pumping level significantly below that required for the observation of significant amplified spontaneous emission in a neat dye solution, such systems may find applications as novel displays, switches, and sensors. In this presentation we compute the emission properties from a colloidal suspension of titania particles in a Rhodamine 640 in methanol dye solution. Since feedback is negligible in these samples, wave interference is ignored in computing average transport within the medium. Consequently, the migration of pump and emitted photons is modeled as a random walk.^1,2,6,7 Rate equations can be used to describe the optical excitation emission and absorption of the medium. In the multiple-scattering limit, the Monte Carlo approach is equivalent to solving a set of coupled nonlinear differential equations describing the diffusion of pump and emitted photons, with a source of photons arising from spontaneous and stimulated emission, and the degree of excitation of various molecular levels.

© 1996 Optical Society of America