[PAST EVENT] Physics Colloquium
The concept of multi-dimensional coherent spectroscopy originated in nuclear magnetic resonance (NMR) where it revolutionized NMR studies of molecular structure and dynamics. In the past two decades, 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 coherent spectroscopy and its applications to study atomic vapors and semiconductor nanostructures. Atomic vapors provide 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 to construct the full Hamiltonian of the system. Besides atomic vapors, optical multi-dimensional coherent spectroscopy is also a powerful tool for studying many-body dynamics and coupling in solid-state systems such as semiconductor nanostructures. I will present several applications in semiconductor quantum wells and self-assembled quantum dots, where unique information about the systems can be obtained from 2D spectra. The technique will also have advantages in studying valley carrier dynamics in atomically thin 2D semiconductors.