Dissertation/Thesis Abstract

Multi-Dimensional Spectroscopy of Semiconductor Quantum Dots
by Bylsma, Jason, M.S., University of South Florida, 2012, 81; 1508620
Abstract (Summary)

The coherent properties of semiconductor nanostructures are inherently difficult to measure and one-dimensional spectroscopies are often unable to separate inhomogeneous and homogeneous linewidths. We have refined and improved a method of performing multidimensional Fourier transform spectroscopy based on four-wave mixing (FWM) experiments in the box geometry. We have modified our system with broadband beamsplitters in all interferometer arms, high-resolution translation stages and the ability to work in reflection geometry. By improving the phase-stability of our setup and scanning pulse delays with sub-optical cycle precision, we are able to reproduce 2DFT spectra of GaAs multiple quantum wells. With the FWM signal reflected from the sample surface instead of transmitted through, we show that very low pulse powers can be used to generate coherent 2D signals from colloidal PbS quantum dots. Dephasing times are particularly difficult to measure in small colloidal quantum dots due to environmental broadening effects from the colloidal growth. We show that low-temperature pure excitonic dephasing can be measured via time-integrated measurements as well as from the cross-diagonal linewidths of 2DFT spectra. Ultrafast sub-picosecond dephasing times are measured at 5 K in 3 nm PbS quantum dots, while excitation-density-dependence is investigated in these dots. By retrieving the global phase with an all-optical method, we are able to retrieve the real-part 2D spectra of PbS quantum dots.

Indexing (document details)
Advisor: Karaiskaj, Denis
Commitee: Batzill, Matthias, Muller, Andreas
School: University of South Florida
Department: Physics
School Location: United States -- Florida
Source: MAI 50/05M, Masters Abstracts International
Subjects: Nanoscience, Condensed matter physics
Keywords: Dephasing, Four-wave mixing, Lead sulfide, Two-dimensional Fourier transform
Publication Number: 1508620
ISBN: 9781267280954
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