Characterization of Aerogel with Spectral Domain Optical Coherence Tomography & Preliminary Analysis of HELIX RICH Flight Data Investigation

Abstract

This thesis characterizes the refractive index and thickness of aerogel tiles and analyzes preliminary flight data from the High Energy Light Isotope eXperiment (HELIX), a balloon-borne detector. Accurate velocity measurements from HELIX's Ring Imaging Cherenkov (RICH) detector are essential to achieve a 3% cosmic-ray isotope mass resolution for Z≤4. This requires aerogel radiators with n = 1.15 at 405 nm to be characterized to the order of 10⁻³ in thickness and 10⁻⁴ in refractive index. Spectral Domain Optical Coherence Tomography (SD-OCT) is introduced here as a non-contact method to simultaneously determine both parameters. The technique meets the experimental requirements, achieving a thickness precision of ±2.1 μm and a group refractive index precision of ±0.0003. A procedure to derive the phase refractive index is also demonstrated. Finally, a preliminary analysis of HELIX flight data is presented here, applying a clustering algorithm (DBSCAN) to identify event morphology in the RICH.