ABSTRACT
Light scattering is usually regarded detrimental to optical connement in conventional lasers. In contrast, in random lasers, the connement is caused by disorder-induced scattering. In strongly scattering media, the lasing is dened by the high-quality modes of the passive system. Thus, by incorporating and optimizing a degree of order, one can dramatically reduce the threshold of a random laser to the values comparable to those of photonic crystal (PhC) lasers. Unlike the latter, where the optical cavity has to be carefully designed and impeccably fabricated, in disordered systems the modes originate from the structure imperfections unintentionally introduced during the fabrication process. Optical gain
CONTENTS
4.4.1 Introduction ...................................................................................................................... 395 4.4.2 Lasing in Random Media ............................................................................................... 396
4.4.2.1 Light Propagation in a Random Medium with Optical Gain ..................... 396 4.4.2.2 Random Lasing in Strongly Scattering Media .............................................. 396 4.4.2.3 Absorption-Induced Connement .................................................................. 397 4.4.2.4 From Random Medium to PhCs with Disorder ............................................ 398
4.4.3 Connement in Disordered PhCs ................................................................................. 398 4.4.3.1 Disorder in Passive and Active PhC Structures ............................................ 398 4.4.3.2 Optimal Degree of Disorder ............................................................................ 399
4.4.4 Lasing in a Disordered PhC Slab ...................................................................................402 4.4.4.1 PhC Slab Laser: Design Considerations .........................................................402 4.4.4.2 Structure Parameters and the PBG .................................................................403 4.4.4.3 Spontaneous Optimization of In-Plane and Out-of-Plane Connement...404
