Colloquium - Optical Multi-dimensional Fourier Transform Spectroscopy
Dr. Hebin Li
JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA
The concept of multi-dimensional Fourier transform spectroscopy originated in nuclear magnetic resonance (NMR) where it revolutionized NMR studies of molecular structure and dynamics and led to the Nobel Prize in Chemistry in 1991. In the past decade, the same concept has been implemented in the optical region with femtosecond lasers. In the experiment, the nonlinear response of a sample to multiple laser pulses is measured as a function of time delays. A multi-dimensional spectrum is constructed by taking a multi-dimensional Fourier transform of the signal with respect to multiple time delays. In this presentation, I will introduce optical multi-dimensional Fourier transform spectroscopy and its applications to study dynamics in quantum systems. Both 2D and 3D spectra of a potassium (K) vapor will be presented. The K vapor provides a simple test model to validate the method, while the obtained 2D spectra reveal the surprising collective resonance due to the dipole-dipole interaction in a dilute gas. By extending the technique into a third dimension, 3D spectra can unravel different pathways in a quantum process and provide complete and unambiguous information of the third-order optical response of the sample. The quantitative insight of isolated pathways can be used to construct the full Hamiltonian of the system. Besides atomic/molecular systems, optical multi-dimensional Fourier-transform spectroscopy is also a powerful tool for studying carrier dynamics in solid-state systems such as semiconductor nanostructures.