Optical Science and Engineering ETDs

Publication Date

Spring 5-14-2022

Abstract

Diode pumped alkali lasers (DPALs) are leading candidates for future high power applications, with many potential utilities for the military, aerospace, communications, and scientific diagnostics. A critical step in their development is measurement and understanding of unwanted ionization processes that occur inside the laser, which decrease efficiency, reduce the usable alkali population, and increase heat load. In this dissertation, direct measurement of the ionization rate of a cesium DPAL gain medium are made for the first time, via application of an ion chamber diagnostic. Results will demonstrate that the rate of ionization is slow compared to pump absorption, with a maximum of less than one ionization event for every one million pump photons absorbed (<1 ppm). The slow ionization rate will be shown to be accurately predicted to within an order-of-magnitude via computer simulation based on known ionization processes.

Ion chambers will be shown to be effective diagnostics for DPAL ionization rate measurement. Plasma production rates in the experiment were orders-of-magnitude above typical conditions, so additional research was done to ensure the accuracy of the diagnostic in this high plasma density regime. Unique processes in the dense plasma are: (1) space-charge limited ion drift, (2) Debye shielding preventing the electric field from penetrating a bulk plasma region, and (3) ambipolar diffusion across the bulk with possibly elevated electron temperature. Although a variety of processes occur only in a high density ion chamber, none of these processes prevent accurate measurement of ionization rate under DPAL conditions.

Degree Name

Optical Science and Engineering

Level of Degree

Doctoral

Department Name

Optical Science and Engineering

First Committee Member (Chair)

Wolfgang Rudolph

Second Committee Member

Timothy Madden

Third Committee Member

Greg Pitz

Fourth Committee Member

Paul Schwoebel

Fifth Committee Member

Payman Zarkesh-Ha

Keywords

Diode pumped alkali laser, DPAL, ion chambers, cesium, laser induced ionization, Thomson model

Document Type

Dissertation

Language

English

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