Probing Tiny-Scale ISM Structure with a New Mode on Parkes

<p dir="ltr">Early studies of the Galactic Hi suggested a lack of structure below parsec scales in the atomic interstellar medium (ISM). However, later observations revealed structure on much smaller spatial scales, comparable to the size of the solar system, within the cold neutral medium (CNM) of the ISM. These tiny-scale features are now known as Tiny-Scale Atomic Structure (TSAS). TSAS is typically studied by searching for small changes in optical depth over astronomical unit (AU) scales. There is still no consensus on their energetics, geometry, or prevalence.</p><p dir="ltr">This thesis contributes to this field by testing for the presence of TSAS using pulsar Hi absorption observations employing a novel High Resolution Spectral Fold Mode (New Mode) commissioned at the Parkes radio telescope. Although no conclusive TSAS detections were made within the scope of this work, the technical viability of the new observing mode was successfully demonstrated along with the development of a working data analysis pipeline. This study lays the foundation for future long-term monitoring and an expanded pulsar sample utilizing the New Mode.</p>