Optical Science and Engineering ETDs

Publication Date

Summer 1-31-2017

Abstract

Recent progress in ultrafast laser science has made it possible to synthesize and control complex electromagnetic waveforms down to sub-femtosecond timescales. These tailored ultrashort laser pulses can generate coherent bursts of electromagnetic radiation in the extreme ultraviolet (XUV) and terahertz spectral regions with durations reaching the attosecond regime in the XUV region. This is accomplished by coherently controlling electronic motion in gas plasma targets. With these novel radiation sources, ultrafast time-resolved spectroscopy can be performed on a large variety of materials. Knowledge of the spectral phase of an ultrashort pulse is crucial for many applications. There are a variety of ways to fully characterize the electric field but usually, involve an elaborate setup. It is highly desirable to have a method of pulse characterization without such complications. In this work, we introduce an algorithm that retrieves the electric field from the measured fundamental and two nonlinear spectra using an iterative process. This measurement technique is insensitive to optical alignment and imperfections of the beam spatial profile. The control of electronic motion enables the generation of a wide range of coherent electromagnetic radiation. In this dissertation, we have combined the fundamental laser beam with its second harmonic to simultaneously generate extreme ultraviolet (XUV) and terahertz radiation. Synchronous pulses in widely separated spectral regions opens the possibility of powerful time-resolved spectroscopy. We introduce an intuitive semi-classical model based on the well-known three-step description to explain the observed XUV and terahertz correlations. The transparency of this model provides an intuitive physical understanding of the complex features observed in the measured XUV spectra. Key insights are obtained from this model by identifying the effect of second harmonic generation efficiency and the interference of short and long electron trajectories. Ultrashort bursts of electromagnetic radiation are powerful tools for time-resolved spectroscopy. Availability of short pulse durations over a broad spectral range aids the investigation of electron transport in a large variety of materials. We have utilized ultraviolet and XUV ultrashort pulses to probe electron transport in several inorganic scintillators. Scintillators are important because they absorb high energy photons and convert this energy to visible luminescence. Excitation and conversion to visible fluorescence takes place on a timescale of tens of picoseconds. Ultrashort bursts of XUV are an ideal excitation source for these studies. The conversion to visible fluorescence is not 100% efficient as there are competing relaxation processes that can be identified from rise and decay time of the luminescence. The results from such measurements can provide guidance in the engineering of more efficient scintillators for high energy radiation detection.

Degree Name

Optical Science and Engineering

Level of Degree

Doctoral

Department Name

Optical Science and Engineering

First Committee Member (Chair)

Mansoor Sheik-Bahae

Second Committee Member

Jean-Claude Diels

Third Committee Member

Mani Hossein-Zadeh

Fourth Committee Member

Markus Hehlen

Keywords

Ultrafast, Ultrashort, Time-resolved spectroscopy, High harmonic generation, Terahertz generation

Document Type

Dissertation

Language

English

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