Speaker
Description
On Behalf of the LiquidO Collaboration
Particle tracking and identification are important for rare-event searches and can be achieved using physical detector segmentation in scintillation and Cherenkov detectors. Virtual segmentation within a monolithic active volume can be achieved using an opaque medium that stochastically confines emitted light near its origin. This concept, first proposed and demonstrated by the LiquidO collaboration, offers excellent spatial resolution for large detector volumes, leveraging event topology reconstruction even without physical segmentation. Wavelength-shifting fibers can be distributed in the opaque detector volume to absorb the generated photons, re-emit them at longer wavelengths, and guide the light to photodetectors at each fiber end. Event topology can be reconstructed from the fiber-hit pattern, known fiber positions, and photon timing, which is then compared to a Monte Carlo light-transport model. Accurate topological reconstruction requires detailed knowledge of the refractive index, absorption length, and scattering length of the active medium. We introduce a new time-resolved method tailored to characterizing highly scattering media, where a picosecond laser pulse is injected at the sample surface, and the resulting surface-wavefront expansion is imaged with an intensified, fast-gated camera. Time-integrated measurements exhibit inherent ambiguity when determining absorption and scattering lengths independently, while imaging of the expanding wavefront allows the effects of scattering and absorption to be effectively separated. The time and spatially resolved expansion profiles are compared to a Monte Carlo light-transport simulation to determine the scattering and absorption lengths. We present the initial qualitative comparisons of the experimental and simulation time-resolved expansion profiles, demonstrating their good agreement. Understanding the optical properties of scintillators is essential for optimizing detector geometry and scintillator composition, which will benefit neutrino detection and rare-event searches using the LiquidO technology.