Spatial and spectral characterization of micrometer scale soft x-ray emitting laser-produced plasmas

The principal goal of the work presented in this thesis is to investigate physical behaviors of both the morphology i.e. shape and size, and the emission energy / wavelength and intensity of soft x-ray emitting laser-produced plasmas. Underpinning these primary objectives is to do so using small scale, affordable experimental equipment and new technologies coupled with modeling methods. This research is undertaken with the goal of understanding laser-produced plasma behaviors in its own right, however this work is part of a larger research endeavor ’xLuminate’, the goal of which is to create and utilize a laser plasma based x-ray light source. Chapter One serves as an Introduction to the thesis and motivation for the work. Chapter Two outlines the fundamental theories that guide much of this research. The work presented in the next four chapters is in preparation for submission to journals for publication or is already published. In Chapter Three the spatial morphology of soft x-ray molybdenum laser plasmas is investigated. An algorithm to infer the true plasma size is developed and discussed, and the spatial dependence of the plasma x-ray emission size of molybdenum plasmas is shown; the importance here lies in the determination of the true plasma area, essential for radiance calculations. In Chapter Four, the design and implementation of a small scale, affordable, commercial CMOS camera based transmission grating spectrometer is discussed. Spectra of several x-ray emitting plasmas are revealed. The utility of the work presented in this chapter lies in the design of a compact, affordable CMOS detector based spectrometer that can operate in gas environments. In Chapter Five a radiation hydrodynamics code is used to benchmark and model the spatial and spectral behaviors of soft x-ray tin laser plasmas. The work detailed in this chapter facilitates the inference of the true plasma emission area. This work can also aid in i) exploratory modeling of the parameter space associated with the creation of laser-produced plasmas, which is large, and ii) predictive radiance calculations. In Chapter Six, i) the morphology of soft x-ray plasmas of molybdenum and iron in an ambient helium buffer gas and ii) spectroscopy of a secondary x-ray emission volume observed in iron and scandium is investigated. This chapter highlights that in pressures of the order of hundreds of millibar of helium gas, the soft x-ray morphology of the laser plasmas produced is marginally impacted, which is important from an x-ray light source perspective that would employ helium as a debris mitigator. Furthermore, a secondary x-ray emission region in front of the target is imaged, and characterized.