Photon detection in noble element detectors is a crucial technique in modern physics, particularly in searches for rare events such as neutrinoless double beta decay or neutrino oscillation studies.
When charged particles interact within a noble element, they excite or ionize its atoms, leading to the emission of vacuum ultraviolet (VUV) scintillation light. This light can be used in particle detectors for triggering, calorimetry, position reconstruction or particle identification.
The efficient detection of the scintillation light remains an unsolved problem: the wavelengths involved make the detection highly non trivial since most photosensors operate on the visible range, and the few ones that can detect those wavelengths have a prohibitive price. Given the size of next-generation TPCs, using those VUV photosensors is not affordable. Instead, noble element detectors often employ wavelength shifters, materials that absorb VUV photons and re-emit them in the visible spectrum, making them easier to detect.
Those WLS material are often used in combination with reflectors or light guides (e.g. optical fibers) that use total internal reflection to channel scintillation light efficiently to photosensors, minimizing photon loss over long distances.