Lasing in disordered media

Abstract

We review our recent work on lasing in active random media. Light scattering, which had been regarded detrimental to lasing action for a long time, actually provided coherent feedback for lasing. We also trapped laser light in micrometer-sized random media. The trapping was caused by disorder-induced scattering and interference. This nontraditional way of light confinement has important application to microlasers. The threshold of ranodm laser can be reduced by incorporating some degree of order into an active random medium. Our calculation result shows that by optimizing the degree of order one can dramatically reduce the threshold of random laser to the values comparable to those of photonic bandgap defect lasers.

Random Laser Action in Dye-Doped Polymer Media with Inhomogeneously Distributed Particles and Gain

“…Random lasers (RLs) are light sources that can generate nearly coherent light with the use of scattering media with gain [1][2][3][4][5][6]. As the optical feedback for lasing is provided by the multiple scattering of light instead of well-defined cavities, the random spatial distribution of the refractive index in the media directly affects the random lasing action.…”

Spatial distribution of optically induced atomic excitation in a dense and cold atomic ensemble

“…Cold and ultra-cold atomic ensembles are currently of significant interest for a wide range of practical applications in metrology, development of frequency standards, the possibility of cold-atom based random lasing [1][2][3][4][5], and quantum information science [6][7][8][9][10][11][12][13][14]. The efficacy of such practical applications depends substantially on the optical thickness of these ensembles.…”

Zinc oxide ultraviolet light-emitting devices : design and fabrication.

“…The path length over which a photon travels before generating another photon is defined as the generation length (l gen ) and it is approximated to the gain length (l g = path length over which the light intensity is amplified by a factor of e) [236]. Once this gain length equals to the average path length (l pat = average distance that a photon travels before leaving the medium), the number of photons increase rapidly [236]. Mathematically, it is shown that the solution to the diffusion equation, including optical gain, increases exponentially [237].…”

“…Mathematically, it is shown that the solution to the diffusion equation, including optical gain, increases exponentially [237]. At this threshold condition, a critical volume (V th ) is hypothesized by the relation [236], to a rapid increase of photons at these wavelengths [238].…”

“…Moreover, a threshold is observed in the light-light curve, accompanied with distinct sharp peaks appearing in the emission spectrum. The number of sharp peaks increases as the pump power increases because more closed-loop cavities are having the gain greater than the loss [236]. Another characteristic for this type of laser is that these lasing peaks in the emission spectra can also be detected and changed with different observation angles.…”