Enhancement of the DUNE FD1 X-ARAPUCA Photon Detection Efficiency and upgrade of the FD2 Photon Collector

The Photon Detection System (PDS) of the first two DUNE far detectors (FD1 and FD2) is composed of 6000 and 672 photon detection units respectively, named X-Arapuca, of different size and geometry. The PDS will complement and boost the DUNE LArTPC for the detection of non beam events: the prompt light detection will improve their tagging, and at low energies it will enable the trigger and the calorimetry of the supernova neutrinos. The X-Arapuca unit is an assembly of several components: its Photon Detection Efficiency (PDE) depends both on the design of the assembly and on the grade and the coupling of the individual components. The X-Arapuca PDE is the driver of the Photon Detection System sensitivity, that in turn determines the sensitivity of the DUNE physics reach for the detection of core-collapse supernova within the galaxy and for nucleon decay searches. In this work we present an update of the absolute PDE of the FD1 X-Arapuca baseline design, measured in laboratory: 160 units of this are deployed in the scale 1:20 FD1 prototype hosted in the NP04 cryostat at the CERN neutrino platform. Further we show how to change the baseline design of the FD1 X-Arapuca, allowing to double its PDE. Finally we review a few selected features of the photon collector of the sixteen FD2 X-Arapuca recently deployed for the FD2 scale 1:20 prototype at CERN in the NP02 cryostat, and of the last six units that integrate the latest advancements.