Photon Detector Development for the Vacuum Ultraviolet Frontier

How is the universe evolving and what roles do dark matter and dark energy play? What is the nature of dark matter and dark energy? What are the fundamental particles and fields? Why is there more matter than antimatter? What is the nature of neutrinos?
To answer these fundamental physics questions, the next generation flagship experiments in neutrino and dark matter will employ noble elements (argon and xenon) as active targets for particle detection. These internationally-leading experiments will rely on detection of light emitted in the vacuum ultraviolet (VUV) wavelength range. Argon and xenon scintillate in the 120-140 nm range and 165-185 range, respectively. This is a problematic region for light detection, where current photodetection technologies perform poorly. Indeed, efficient detection of light down to a single photon using optoelectronic devices is a key theme in the UK’s Quantum Strategy, and extending the detectable spectral range is an established goal of quantum imaging research. We target this extension to VUV, where the decreasing wavelength poses challenges for detection due to the rapid increase of the reflectivity. The state of the art in large-area silicon sensor array technology is Silicon Photomultipliers (SiPMs) with unsatisfactory performances of photon detection efficiency between 15% (Hamamatsu, at 178 nm) and 22% (FBK Low Field UV optimized), dropping to 10% for 128 nm.
With this project, we aim at boosting the quantum efficiency and collected number of photons for VUV sensitive photon sensors via a strategy that combines smart sensor designs, the use of 2D materials, and the application of novel readouts. This will unlock the potential of a wide range of tonne- and kilotonne-scale neutrino and dark matter experiments such as DUNE, NEXT, DarkSide, LZ and nEXO. These experiments will need to instrument large readout areas (10–100 m2) both at room temperature (DUNE near detector and NEXT experiments) and in cryogenic conditions (DUNE far detectors, DarkSide, LZ and nEXO experiments).  The technologies pursued aim to reach at least a factor of two improvement in the VUV wavelength range relevant for noble elements, whilst preserving comparable cost per unit area and timing performance.
Our strategy is to develop high-efficiency single photon sensitive devices using novel graphene coatings on silicon and selenium, and metaoptics. Our R&D program comprises the development of three distinct lines of technology and their integration into detectors: SiPMs with increased VUV detection efficiency  (WP1), amorphous selenium sensors (WP2), and metaoptics devices (WP3). While the three technologies are distincts, they are highly complementary and can be combined for further improvements. We also propose a common testing strategy (WP4) to characterise the relative noise and quantum efficiency of the sensors in the VUV, and will assess the benefits of merging metaoptics and the novel photosensors. Such a common strategy will optimise not only the performances of each design, but will also allow us to abate the testing cost and lab time. This program leverages capability and infrastructure across a range of UK institutes for the DUNE and DarkSide programmes.