Date of Award

11-2023

Document Type

Dissertation

Degree Name

Ph.D.

Organizational Unit

College of Natural Science and Mathematics, Physics and Astronomy

First Advisor

Mark Siemens

Second Advisor

Davor Balzar

Third Advisor

Dinah Loerke

Fourth Advisor

Schuyler Van Engelenburg

Keywords

Multidimensional coherent spectroscopy (MDCS), Quantitative analysis, Homogeneity, Optics, Photovoltaics, Semiconductors

Abstract

Multidimensional coherent spectroscopy (MDCS) is a quickly growing field that has a lot of advantages over more conventional forms of spectroscopy. These advantages all come from the fact that MDCS allows us to get time resolved correlated emission and absorption spectra using very precisely chosen interactions between the density matrix and the excitation laser. MDCS spectra gives the researcher a lot of information that can be extracted purely through qualitative analysis. This is possible because state couplings are entirely separated on the spectra, and once we know how to read the data, we can see how carriers transport in the frequency domain just from a glance of the spectrum. With that said, as we study more complex mechanisms and want to extract even more information from MDCS, we must employ new experimental methods, and quantitative approaches. This thesis will focus on just that.

This thesis begins by motivating why we use MDCS, and then we spend the next few chapters just working to understand MDCS. This is accomplished by deriving the nonlinear polarization which causes the emission of the MDCS signal. Next, we consider more conventional electronic spectroscopies as a way to familiarize ourselves with the topic that will be discussed in the more complicated electronic spectroscopy that is MDCS. Once we have been primed with these conventional spectroscopies we will go into great detail describing our specific version of MDCS. This will include everything from the setup and execution of the experiment to how we can read MDCS spectra, and what conclusions we can make just from qualitative analysis. We will be able to identify homogeneous and inhomogeneous broadening, state coupling, and carrier transitions. Within this section we will discuss some quantitative lineshape analysis that has been done before to measure the homogeneity and inhomogeneity of a resonance measured through MDCS.

Next will begin the original works that were accomplished. First, we will see the time-resolved Sommerfeld enhancement of absorption. We show how we can go from a conceptual model to a mathematical model to be used for quantitative analysis of data that is extracted from an MDCS spectrum. We will explain why this type of measurement is not possible with more conventional electronic spectroscope, and by fitting our data to this mathematical model, we will ultimately describe the mechanism that governs the carrier transport in semiconductors near the band edge.

After this we will shift gears to talk more about the relationship between the density matrix and the excitation lasers. As it turns out the impulsive material response of the system is contaminated by the laser spectrum, and the density matrix which we detect ends up being a convolution between the two. This means that when we are trying to understand the electronic properties of an optically active system, we are actually reading the interaction between the laser and the system itself. We will derive how we can remove the laser spectrum from the measurement, and then we will show data proving that this method of removing the laser actually works. Thus, the quantitative lineshape analysis techniques that were derived for impulsive interaction Hamiltonians can be used even for real laser pulses which are not impulsive in nature.

The last novel topics are currently works in progress. We will show real data taken on perovskite solar cells where we address many of the drawbacks in the way spectroscopy is done on solar materials. Essentially, we will be taking measurements in conditions more like how solar cells are deployed for use in commercial settings. This means we take our measurements at room temperature, with laser power on the same order of magnitude of the sun, and detect photocurrent, instead of optical emission. We show the data with the laser spectrum contribution removed and make some observations on this preliminary data.

Finally, we will look at what the lab is working on now. Which is diving deeper into the solar cell world by taking I-V curves while doing MDCS. I-V measurements are a very common measurement used to determine the efficiency of a photovoltaic semiconductor. We believe, and have some preliminary data showing, that we may be able to determine the efficiency of specific transitions in semiconductor, by varying the applied potential for a particular MDCS spectrum, measuring the photocurrent, and then integrating over the peaks that represent particular transitions. These potential-dependent integrated areas should tell us about the efficiency of that transition.

Copyright Date

11-2023

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Adam Halaoui

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

140 pgs

File Size

27.0 MB

Discipline

Physics, Materials Science, Optics

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