Localization of laser light in active random media

H. Cao, J. Y. Xu, G. S.-H. Chang, S. T. Ho, E. W. Seelig, X. Liu, R. P. H. Chang

Department of Physics and Astronomy, Materials Research Center, Northwestern University, Evanston, IL 60208

We have observed rand om laser action in highly disordered semiconductor powder and polycrystalline films. Since the scattering mean free path is less than the emission wavelength, recurrent light scattering arises and provides coherent feedback for lasing. Above the lasing threshold, discrete lasing modes appear in the spectrum in addition to a drastic increase of emission intensity. Our measurement of spatial distribution of laser light intensity indicates that photons are localized in spatial regions of the size on the order of optical wavelength. The laser emission from the random media can be observed in all directions.

In addition to macroscopic-scale random media, we have observed lasing action in micrometer-sized random media. This discovery leads to the fabrication of microlaser with disordered medium. Anderson localization of light provides a new physical mechanism of optical confinement for microlaser.