  Future lepton colliders such as the FCC-ee, CEPC, ILC, or a muon collider
will collect large data samples that allow precision physics studies with
unprecedented accuracy, especially when the data is collected by innovative
state-of-the-art detectors. An electromagnetic calorimeter based on
scintillating crystals, designed to separately record Cherenkov and
scintillation light, can achieve precision measurements of electrons and
photons without sacrificing jet energy resolution, given adequate light
collection efficiency and separation. This paper presents initial measurements
from a program aimed at developing such a calorimeter system for future
colliders. We focus on using PbF2 crystals to enhance the understanding of
Cherenkov light collection, marking the first step in this endeavor.
