Investigation of Aero-Optical Wavefront Measurements using Laser-Induced Breakdown Sparks

This dissertation focuses on the problem of improving wavefront measurements that use the light from a laser-induced breakdown (LIB) spark as the light source. The contextual motivation involves the development of instruments for in-flight measurement aero-optical flow that is self-contained and non-intrusive. Previous studies have shown that wavefronts measured with the light from an LIB spark have dominant low-order Zernike components, specifically defocus, vertical astigmatism, and horizontal coma, that are not characteristic of aberrations on wavefronts passing through flows of interest such as a boundary layer. This research explores different models of LIB sparks to determine if the amplitudes of these Zernike aberrations can be predicted based on variations in spark attributes such as length and position that arise in spark to spark ignitions. Principal component analysis of experimentally obtained spark wavefronts revealed that the first principal component consists primarily of defocus and that next several principal components are combinations astigmatism, coma, and trefoil, all of which are predicted to arise from displacements of simple point source models. Investigation into more complicated models revealed that the light captured from wavefront sensors predominantly come from the surface of the spark.