Lasing Phenomena in Mixed Random & Ordered Media

Northwestern University, Evanston IL

Investigators

Abstract

0244457 Cao Solid state lasers, due to their large capacity to transmit information, have revolutionized the way we communicate, greatly enhancing the quality of our lives. One of the major challenges in the development of these lasers has been the growth of perfect and precise thin film crystal layers. Thus, the time between invention of the solid state lasers and their commercialization has taken several decades. A basic, lingering science question has been whether or not lasing can take place in a completely disordered (or random) medium. And, if so, would the laser operate efficient enough for applications? Recently, the investigators have discovered that they can achieve coherent lasing in random media. They found that disorder-induced light scattering not only provides coherent feedback for lasing, but also leads to spatial confinement of laser light in micrometer-sized random media. They fabricated a new type of microlaser with disordered medium. However, the threshold for lasing is still too high for practical use. This high lasing threshold results from incomplete trapping of light in the random medium. For the proposed project the investigators plan to introduce order into a random medium to achieve better localization of light, thus lowering the lasing threshold. The research program will focus on both experimental and theoretical studies of lasing phenomena in two-dimensional and three-dimensional partially ordered random media. Such lasing media consist of uniform arrays of ZnO nanorods or nanospheres with variable degrees of disorder. The proposed activities will start with theoretical analysis and numerical simulation to predict structures that meet the optimal conditions for lasing. Using the best design criteria, nanofabrication of lasers will take place followed by structure characterization, and optical measurements of these random lasers. The researchers envision that the success of their proposed program will enrich the research and education environment of students, teachers, and their colleagues. In particular, they foresee the following areas in which their work will deliver the most impact: (1) Application to research-Since a low-threshold random laser is much cheaper to manufacture than a single-defect photonic crystal laser, it may be a low-cost alternative in many applications. (2) Integrating research with education-The investigators have extensive experience in the integration of education with research involving pre-college students, undergraduates, and graduate students. They will continue to have joint group meetings where recent research results are discussed among the students and the investigators. (3) Science content and curriculum development-Based on the success of the NSF-funded Materials World Modules, the investigators will be involved with the development of a dynamic, customized, web-based course for pre-college and first year undergraduate students in the area of "light wave phenomena in materials". Basic concepts of light reflection, refraction, and scattering from surfaces and nanostructured materials will be discussed. They will develop these concepts by giving a series of examples from industrial applications and our environment. In addition, students will learn the many applications of how light can be generated, manipulated and detected in materials. This course will be web-based, with different levels of difficulty. They will collaborate with their colleagues around the world to up-date and revise the content any time. In the end this will be a global course with many exciting contributions. (4) Outreach and global dissemination-The investigators will post their research results in the Global Research Gallery of the Northwestern International Virtual Institute (IVI) for public viewing. Lectures and seminars relating to the proposed research will be video taped and stored in the Lecture Hall of the IVI for others to view. (5) Summer Research Program for science teachers and underrepresented students-The investigators will continue to host in their laboratories science teachers and underrepresented students to perform summer research programs that are sponsored by the NSF-funded Materials Research Science and Engineering Center at Northwestern University.