Lasing in nanocomposite random media

Scattering of light by disordered structures is a common phenomenon in our daily Life. For many scientific applications, scattering is often treated as a detrimental effect. However, recent development in the field of nanophotonics shows that scattering in disordered nanostructures can enable new functionalities, including the unexpected property of random lasing. A random laser is different from a traditional laser in that the feedback amplification is not provided by a cavity formed by reflection components, but by disorder-induced scattering. Depending on the nature of disordered nanostructures, which can range from a few nanometers to several hundreds of nanometers in size, disorder-induced scattering can provide intensity feedback or amplitude feedback. Thus random lasers are classified into two categories: incoherent random lasers and coherent lasers. During the past two decades, many disordered nanostructures, including laser dye in colloidal systems, photonic crystals, polymeric matrices, rare earth doped nanopowders, quantum dots, semiconductors, and biological tissues have been proposed and demonstrated to form high-performance random lasers. Excitation mechanisms have included optical and electrical pumping. In the former, besides single photon excitation, multiphoton pumped upconversion random lasing has also been demonstrated. In this review, we describe the physics that explains the optical properties of disordered nanostructures and scattering used to develop the random lasers, particularly discussing the rote of modes in random lasers. We then present the current state-of-art of fabrication and processing of various disordered nanostructures for the development of random lasers, including techniques to manipulate characteristics such as tunability and directionality. In this context, random fiber lasers will be discussed, as they play an important role in applications of random lasers. It will also be pointed out that random lasers keep the spatial and the temporal coherence characteristic behavior of conventional lasers, as well as the Poissonian statistics well above the threshold. Recent achievements in upconversion lasing, Raman lasing and SPASER lasing in a random medium will also be covered. Then we discuss the impact of random lasers in cross-disciplinary areas such as astrophysics. A major emphasis of this review is to cover the various applications that have already emerged. The review concludes with the author's views on future perspectives, including some envisioned futuristic applications. (C) 2015 Elsevier Ltd. All rights reserved.