Conference Hall 322, Science Building
Colloquium:
Time: 10:00 am, Tuesday, June 19, 2012
Title: Measurements of microwave and optical propagation of diffusive and localized waves
Speaker: Professor Azriel Z. Genack
Queens College of the City University of New York
Abstract:
I will discuss the challenges in measuring the statistics of steady state and pulsed microwave and optical propagation in random media as well as the surprising confluence of factors that make it possible to make detailed and accurate measurements. These measurements give the statistics over a random ensemble of statistically equivalent samples as well as the statistics within a single sample. Statistics in single samples are crucial for imaging, focusing and enhanced transmission in random media with potential applications in biomedical imaging and telecommunications. The essence of our findings is captured in a string of relationships between localization parameters that encapsulate diverse aspects of wave propagation. These include the average value, fluctuations and correlation of intensity, total transmission and conductance, the participation number of transmission eigenvalues and the ratio of the width and spacing of modes of the random medium. Finally I will discuss efforts to find the energy distribution within random samples and to relate this to characteristics of transmitted radiation.
This work was performed with Jing Wang, Zhou Shi, Jongchul Park, Xiaojun Cheng and Matthieu Davy and was supported by the National Science Foundation.
Seminar + blackboard discussions:
Time: 9:30 am, Wednesday, June 20, 2012
Title: Transport of Localized Waves in Open Media
Speaker: Professor Zhao-Qing Zhang (张昭庆)
Department of Physics and William Mong Institute of Nano Science and Technology
The Hong Kong University of Science and Technology
Abstract:
Since the concept of wave localization in random media was first proposed by P.W. Anderson more than 50 years ago, Anderson localization has become an important phenomenon in condensed matter physics. The phenomenon is ubiquitous in wave propagation in random environments including electrons in dirty metals, classical waves in random media and matter waves in random potentials. In the first part of this talk, a brief introduction of the Anderson localization will be given. In particular, some important concept and theory will be mentioned and discussed such as the weak localization (WL) effect, which is the most important wave interference effect that causes the localization of waves, and the self-consistent localization theory (SCLT). In 2000, SCLT was generalized to random systems in open media and the concept of position-dependent diffusion coefficient was introduced.
In the second part of my talk, some results of our recent studies on the static and dynamic transport of localized waves in both one-dimensional and quasi-one-dimensional open media will be presented. In particular, it will be shown that the SCLT with position-dependent diffusion coefficient fails to describe the dynamical microwave transmission measurements at long times. This strongly indicates the importance of resonant transmissions in the transport of waves in localized samples. A dynamic single parameter scaling model that incorporates only isolated resonant transmissions and ignores necklace states will be discussed. In the static limit, an analytic result obtained by using supersymmetric field theory will be presented. It is shown that the theory is capable of capturing all rare resonant transmissions and gives rise to a novel scaling behavior for the local diffusion coefficient.
