Optical Multidimensional Fourier Transform Spectroscopy
|Date/Time:||Monday, 06 Feb 2012 - Wednesday, 08 Feb 2012|
|Location:||Physics Hall Room 5|
(JILA, Nat'l Inst. of Standards and the University of Colorado)
The concept of multidimensional Fourier transform spectroscopy originated in NMR where it enabled the determination of molecular structure. In either NMR or optics, a sample is excited by a series of pulses. The key concept is to correlate what happens during multiple time periods between pulses by taking a multidimensional Fourier transform. The presence of a correlation, which is manifest as an off-diagonal peak in the resulting multidimensional spectrum, indicates that the corresponding resonances are coupled. Migrating multidimensional Fourier transform spectroscopy to the infrared and visible regimes is difficult because of the need to obtain full phase information about the emitted signal and for the phase difference between the excitation pulses to be stable and precisely incremented. I will give an introduction to optical two-dimensional Fourier transform spectroscopy and then present our use of it to study a potassium vapor and excitonic resonances in semiconductors. The atomic vapor provides a simple well understood system for which the two-dimensional spectrum can be calculated. However, the presence of inter-atomic interactions are also revealed as unexpected peaks in certain spectra. By extending the technique into a third dimension, it is possible to determine the Hamiltonian. In semiconductors, our results show that many-body effects dominate the light-matter interaction for excitons in semiconductors and provide a rigorous and quantitative test of the theory. We can isolate excitonic molecules, known as biexcitons. The technique also allows non-radiative coherences, such as zero-quantum and two-quantum coherences, to be isolated and measured.
Steven T. Cundiff received the B.A. degree in Physics from Rutgers University in 1985. He received M.S. and Ph.D. degrees in Applied Physics from the University of Michigan in 1991 and 1992, respectively. He spent two years as an Alexander von Humboldt Fellow at the University of Marburg, Germany and then joined Bell Laboratories in Holmdel N.J. as a post-doctoral Member of Technical Staff. In 1997 he joined JILA, a joint institute between the University of Colorado and the National Institute of Standards and Technology (NIST), in Boulder, Colorado. He served as Chief of the NIST Quantum Physics Division from 2004 to 2009. Currently, he is a Fellow of JILA, a Physicist with the NIST Quantum Physics Division and a Professor Adjoint in the University of Colorado Department of Physics and Electrical and Computer Engineering Department. He is a Fellow of the Optical Society of America and of the American Physical Society. He received a Humboldt Research Award in 2010 and the Meggers Award from the Optical Society of America in 2011. His current research interests include optical multidimensional Fourier transform spectroscopy, quantum optical spectroscopy of semiconductors, optical arbitrary waveform generation and modelocked laser development.