Rajarshi Roy - US grants

The coherence properties of semiconductor lasers determine the limits of their application in optical communication channels, computation and storage. Before these limits can be enhanced, the sources of laser instability and noise need to be understood. Through novel statistical experiments and theoretical calculations, we propose to discover new principles for the development of stable lasers and noise reduction by geometric reconfiguration, manipulation of material properties, and the application of electronic feedback techniques. We will probe correlations between operating parameters and laser response over time scales from seconds to picoseconds. We will study (i) reflection induced instabilities, (ii) mode partition noise and mode-hopping, (iii) the linewidth (power dependent and independent) and dynamics of solitary and external cavity semiconductor lasers and (iv) low frequency 1/f noise. The generation of quantum states with sub-Poissonian statistics by semiconductor lasers will be examined. The role of deterministic chaos and quantum noise in reflection instabilities will be studied with very fast transient digitizers. We expect to develop design strategies for constructing stable lasers. Monte Carlo simulations will be used to test hypotheses on the origins of laser instabilities in conjunction with the experiments. The lasers thus developed could be used for information processing, pumping solid state lasers and for precision measurements.

This research program will study control of the chaotic dynamics of solid state laser systems that contain intracavity nonlinear elements. These laser systems are rapidly finding important applications in optical communications and information processing, materials processing, medicine and laser radar. Specific goals include novel pulsed operation and complex periodic waveform generation by semiconductor and diode-pumped solid state lasers. These goals will be achieved through the development of control techniques that are applicable to chaotic systems. Control algorithms that have very recently been developed by Ott, Grebogi and Yorke will be implemented on laser systems to obtain specific complex waveforms that cannot be generated by stable systems. This will require novel electronic and optical techniques for fast feedback and control of laser parameters. We will attempt to control multimode laser systems and develop the techniques for switching between complex periodic waveforms, such as the antiphase states demonstrated recently in a diode-pumped solid state laser. Such studies should have an impact not only on the development of new laser systems and optical communications, but on the control of systems of chemical reactions and biological systems as well. A fundamental understanding of the statistical nature of chaotic dynamics and the influence of quantum noise in chaotic lasers will be developed.

Professor Rajarshi Roy of the University of Maryland, with Co-PIs Kenneth Showalter of the University of West Virginia and Harry Swinney of the University of Texas ? Austin, will conduct an Advanced Studies Institute on ?Hands-on Research in Complex Systems? at the University of Buea, Buea Cameroon, for two weeks in July-August 2010.

Intellectual Merit: The ten faculty will be eminent scientists from the U.S. who have conducted frontier research using tabletop instrumentation and who have published their results in journals such as Nature, Science, and Physical Review Letters along with their partners from Cameroon and other African countries. They will be assisted by ten U.S. advanced graduate students and postdoctoral associates. The unique focus of the ASI will be on hands-on laboratory experiments using inexpensive instrumentation leading to frontier scientific advances in understanding complex systems. The laboratory sessions will be complemented by associated mathematical modeling using the software Scilab (which is similar to Matlab), which is available for download, free of charge. The primary goal of the ASI is to develop collaborations for scientific research with African nations. The ASI participants will be advanced graduate students and young scientists and engineers from developing countries in Africa (and a few participants from developing countries elsewhere). The U.S. faculty will benefit by making lasting contacts with scientists from developing countries. The ASI is sponsored partly by the International Centre for Theoretical Physics (ICTP) in Trieste, Italy; ICTP will provide travel funding for participants from developing nations and administrative support for advertising the school and selecting the participants. The ASI will be co-sponsored by the Ministry of Higher Education of Cameroon, and will be held at the University of Buea which will provide laboratories and lecture rooms for Hands-On Research sessions as well as lodging and meals for all participants from Africa and participating countries.

Broader Impact: Participants from the U.S. and developing countries will work closely together conducting experiments and developing mathematical models. The senior faculty and their assistants (whose participation will be made possible by the support of this grant) will lead the hands-on sessions that are the centerpiece of the ASI. These interactions will naturally lead to long term collaborations and exchanges of personnel. The junior faculty (U.S. graduate students and postdoctoral associates) will benefit not only from the interactions with peers who will become leaders in science and technology in developing nations, but also the school will provide the junior faculty with a unique opportunity to hone their own teaching and leadership skills in a unique multi-cultural environment. The senior faculty will present lectures and tutorials on the experiments and numerical modeling. Table-top experiments are particularly well suited for scientific research in developing countries where resources are limited. The interactive sessions will provide a learning experience for faculty as well as the participants, as we all work together to observe phenomena, explore concepts, and raise questions that warrant further study. Our experience as directors of a Hands-On Research on Complex Systems meeting, held in India in January 2008, was that many participants have reported that their participation was a life-changing experience. Building on our experience in India and responding to the suggestions and criticisms of the participants there, we expect that the Hands-On Research on Complex Systems ASI in Cameroon to have lasting impact on the scientific careers of the faculty as well as the school participants.

This award provides partial funding for an advanced study institute (ASI) on complex systems in physics to be held in Shanghai, China, in June 2012. A team of 12 senior researchers and 24 assistants from the U.S. will join colleagues at Shanghai Jiao Tong University (SJTU) to offer a two-week hands-on course demonstrating table-top experiments in complex non-linear physical systems. About 70 participants, primarily junior faculty members, will be selected from underdeveloped regions of Central and Southeast Asia. The objective is to demonstrate that interesting and productive experiments can be conducted with relatively inexpensive and available materials. This ASI is a successor to similar programs that have been held in Africa, India, and Brazil. The local expenses will be supported by SJTU, and participant expenses as well as administrative costs are sponsored by the International Center for Theoretical Physics (ICTP) in Trieste, Italy.
This workshop will engage leading researchers and well qualified post-doctoral fellows and graduate students with participants from underdeveloped regions in Asia to conduct the table-top experiments as well as to introduce useful computer software to the participants. As has already been demonstrated by the previous Hands-on ASIs, these activities stimulate the curiosity of the participants and raise a variety of interest research questions that they can pursue on their own and in continuing collaborations. In addition to raising research issues in the study of complex phenomena the institute demonstrates useful and effective methods of scientific education. This experience is beneficial to the young U.S. assistants as much as to the Asian participants.

A long-standing and profound problem in astronomy is the difficulty in obtaining deep
near-infrared observations from the ground due to the extreme brightness and variability of the night sky at these wavelengths. The atmospheric emission at 1.0 - 1.7 um arises almost entirely from a forest of extremely bright, very narrow OH emission lines that vary on timescales of minutes. Using an approach known as a fiber Bragg grating (FBG), these emission lines can now be selectively removed, while retaining high throughput between the lines.

Dr. S. Veilleux of the University of Maryland College Park and his international team have carefully refined the application of this technique by incorporating an Integral Field Unit (IFU) FBG input, and have thoroughly demonstrated the efficacy of the approach through in situ tests with existing telescopes and instrumentation. The requested NSF funds are highly leveraged through FBG development at the University of Sydney and spectrograph construction being provided by the NASA Goddard Space Flight Center as well as the University of Maryland. Science applications will initially focus on low-resolution spectroscopy of very faint, transient gamma-ray burst (GRB) sources, which are now known to originate in supernovae located in very distant galaxies, as well as on studies of the galaxies that host these cataclysms. Teaming with Discovery Communications provides an unusual outreach component to the project that will involve students at a variety of levels as well as the general public.

Funding this component of the near-infrared OH emission-line suppression spectrograph is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.