CAREER: Unlocking "forbidden" optical transitions in nanostructures using light with orbital angular momentum

University Of Denver, Denver CO

Investigators

Abstract

Nontechnical abstract: Light with orbital angular momentum (also called "vortex beams" and "twisted light") has generated considerable recent interest because of applications in high-resolution imaging and high-bandwidth communications, but little is known about how twisted light interacts with solid matter. This research explores the use of twisted light to generate new "twisted" quantum electron excitations in nanostructures. Experiments are performed by illuminating cylindrical nanostructures such as rings and dots with light that has tunable orbital angular momentum in order to excite, measure, and control twisted electronic states. The new quantum states accessed in this research could be used in future technologies such as high-bandwidth data storage, computing, and communications. Additionally, this work will be integrated into a new service learning course at the University of Denver in which students will bring these research ideas into neighborhood middle and high schools through hands-on demonstrations. Technical abstract: The objective of this project is to demonstrate and measure unexplored orbital angular momentum (OAM)-activated optical transitions in semiconductor nanostructures. Experiments are performed on quantum rings, dots and wells in order to: 1.) Demonstrate that different orbital states are accessed with twisted light by studying the OAM dependence of transmission spectra; 2.) Measure the dephasing of distorted (OAM-excited) electron and hole wavefunctions with zero spatial overlap, including varying the distribution between center-of-mass and relative-motion angular momentum that is only possible with OAM excitation; and 3.) Control the relaxation of orbital states with OAM-tunable optical pumping. These experiments are enabled by novel multidimensional spectroscopy in which both OAM and wavelength are simultaneously resolved.