Localized random lasing modes and a new path for observing light localization

Costas Soukoulis
Research Center of Crete,
FORTH, Heraklion, Crete, Greece
and Dept. of Physics, and Ames Lab.,
Iowa State University, Ames, Iowa, USA

By using a Finite Difference Time Domain (FDTD) model [1,2] we study the dynamical behavior of random laser systems. We demonstrate [3] that a knowledge
of the density-of-states and the eigenstates of a random system without gain, in conjunction with the frequency profile of the gain, can accurately predict
the mode that will lase first. Its critical pumping rate can be also obtained. It is found [3] that the shape of the wavefunction of the random system remains
unchanged as gain is introduced. The role of the gain is to increase uniformly the amplitude of the wavefunction, without changing its shape. These results
were obtained by the time-independent transfer matrix method and finite-difference-time-domain (FDTD) methods in a 1D model. They can be also analytically
understood by generalizing the semi-classical Lamb theory of lasing in random systems. These findings provide a new path for observing the localization of light.
Our FDTD method, also predicts that relaxation oscillation occurs in some lasing modes. This is in agreement with recent experiment of Cao et al [4] on random lasers.

[1] Xunya Jiang and C. M. Soukoulis, Phys. Rev. Lett. 85, 70 (2000).
[2] X. Jiang and C. M. Soukoulis, in Photonic Crystals and Light Localization in the 21st Century edited by C. M. Soukoulis (Kluwer, Dordrecht, 2001), p. 417.
[3] X. Jiang and C. M. Soukoulis, Phys. Rev. E 65, 025601(R) (2002).
[4] C. M. Soukoulis, X. Junya, J. Y. Xu and H. Cao, Phys. Rev. B 65, 041103(R) (2002).