The Dichroicon: Spectral Photon Sorting For Large-Scale Cherenkov and Scintillation Detectors.

We describe here measurements with a new device, the "dichroicon," a Winston-style light concentrator built out of dichroic reflectors, which could allow large-scale neutrino detectors to sort photons by wavelength with small overall light loss. Photon sorting would benefit large-scale water or ice Cherenkov detectors such as Hyper-Kamiokande or ICECUBE by providing a measure of dispersion, which in turn could allow improved position reconstruction and timing. For scintillator detectors like JUNO, upgrades to SNO+ or KamLAND-ZEN, or to water-based liquid scintillator detectors like Theia, dichroicons would provide effective discrimination between Cherenkov and scintillation light, allowing them to operate as true hybrid detectors. Dichroicons are useful for wavelength discrimination in any photon-starved environment in which detection area is limited. We include measurements with a prototype dichroicon using first a Cherenkov source to show spectral photon sorting works as expected. We then present measurements of two different LAB-based liquid scintillator sources, and demonstrate discrimination between Cherenkov and scintillation light. On the benchtop we can identify Cherenkov light with better than 90\% purity while maintaining a high collection efficiency for the scintillation light. First results from simulations of a large-scale detector are also presented.