Xenon doping of liquid argon in ProtoDUNE single phase

The Deep Underground Neutrino Experiment (DUNE) will be the next generation long-baseline neutrino experiment. The far detector is designed as a complex of four LAr-TPC (Liquid Argon Time Projection Chamber) modules with 17 kt of liquid argon each. The development and validation of the first far detector technology is pursued through ProtoDUNE Single Phase (ProtoDUNE-SP), a 770 t LAr-TPC at CERN Neutrino Platform. Crucial in DUNE is the photon detection system that will ensure the trigger of non-beam events — proton decay, supernova neutrino burst and BSM searches — and will improve the timing and calorimetry for neutrino beam events. Doping liquid argon with xenon is a known technique to shift the light emitted by argon (128 nm) to a longer wavelength (178 nm) to ease its detection. The largest xenon doping test ever performed in a LAr-TPC was carried out in ProtoDUNE-SP. From February to May 2020, a gradually increasing amount of xenon was injected to also compensate for the light loss due to air contamination. The response of such a large TPC has been studied using the ProtoDUNE-SP Photon Detection System (PDS) and a dedicated setup installed before the run. With the first it was possible to study the light collection efficiency with respect to the track position, while with the second it was possible to distinguish the xenon light (178 nm) from the LAr light (128 nm). The light shifting mechanism proved to be highly efficient even at small xenon concentrations (<20 ppm in mass) furthermore it allowed recovering the light quenched by pollutants. The light collection improved far from the detection plane, enhancing the photon detector response uniformity along the drift direction and confirming a longer Rayleigh scattering length for 178 nm photons, with respect to 128 nm ones. The charge collection by the TPC was monitored proving that xenon up to 20 ppm does not impact its performance.

3D printing of composite reflectors for enhanced light collection in scintillation detectors

<div>The present study deals with the fabrication of light-reflecting materials used in pixelated scintillator detectors. For the first time, the reflecting surfaces for pixels of different sizes (from 0.8 to 3.2 mm) were obtained via a low-cost DLP 3D printing technique. The material for the reflectors was the new composite of transparent ultraviolet light-cured resin and TiO₂ as a light-scattering filler. It was observed that TiO₂ showed better performance compare to other pigments such as BaSO₄, hBN or cubic zirconia. The object formation rate was about 1 cm per hour with the possibility to produce several parts simultaneously that simplifies the wrapping procedure. It was found that the regular grooves pattern of the fabricated parts (staircase effect) could increase a light collection from a scintillator. The reflective properties of such surfaces were comparable to conventional reflection coating (e.g., Teflon wrapping).<br></div>Presented at the 2019 IEEE NSS & MIC conference, Manchester, UK. 14 pages, 12 figures, 1 table. Journal reference: Optical Materials V. 108, October 2020, p. 110393.

3D printing of composite reflectors for enhanced light collection in scintillation detectors

<div>The present study deals with the fabrication of light-reflecting materials used in pixelated scintillator detectors. For the first time, the reflecting surfaces for pixels of different sizes (from 0.8 to 3.2 mm) were obtained via a low-cost DLP 3D printing technique. The material for the reflectors was the new composite of transparent ultraviolet light-cured resin and TiO₂ as a light-scattering filler. It was observed that TiO₂ showed better performance compare to other pigments such as BaSO₄, hBN or cubic zirconia. The object formation rate was about 1 cm per hour with the possibility to produce several parts simultaneously that simplifies the wrapping procedure. It was found that the regular grooves pattern of the fabricated parts (staircase effect) could increase a light collection from a scintillator. The reflective properties of such surfaces were comparable to conventional reflection coating (e.g., Teflon wrapping).<br></div>Presented at the 2019 IEEE NSS & MIC conference, Manchester, UK. 14 pages, 12 figures, 1 table. Journal reference: Optical Materials V. 108, October 2020, p. 110393.

Nanograting-Enhanced Optical Fibers for Visible and Infrared Light Collection at Large Input Angles

The efficient incoupling of light into particular fibers at large angles is essential for a multitude of applications; however, this is difficult to achieve with commonly used fibers due to low numerical aperture. Here, we demonstrate that commonly used optical fibers functionalized with arrays of metallic nanodots show substantially improved large-angle light-collection performances at multiple wavelengths. In particular, we show that at visible wavelengths, higher diffraction orders contribute significantly to the light-coupling efficiency, independent of the incident polarization, with a dominant excitation of the fundamental mode. The experimental observation is confirmed by an analytical model, which directly suggests further improvement in incoupling efficiency through the use of powerful nanostructures such as metasurface or dielectric gratings. Therefore, our concept paves the way for high-performance fiber-based optical devices and is particularly relevant within the context of endoscopic-type applications in life science and light collection within quantum technology.

Giant excitonic upconverted emission of two-dimensional semiconductor in doubly resonant plasmonic nanocavity

Phonon-assisted upconverted emission lies at the heart of energy harvesting, bioimaging, optical cryptography and optical refrigeration. It has been demonstrated that the emerging two-dimensional (2D) semiconductors can provide a great platform for efficient phonon-assisted upconversion due to the enhanced optical transition strength and phonon-exciton interaction of 2D excitons. However, the research on the further enhancement of excitonic upconverted emission in 2D semiconductors is almost blank. Here we report the enhanced multiphoton upconverted emission of 2D excitons in doubly resonant plasmonic nanocavity. Owing to the enhanced light collection, enhanced excitation rate and quantum efficiency enhancement arising from Purcell effect, the upconverted emission amplification of > 1000 folds and the decrease of 2 ~ 3 orders of magnitude for saturated excitation energy density are achieved. These findings pave the way to the development of excitonic upconversion lasing, nanoscopic thermometry and sensing, and open up the possibility of optical refrigeration in future 2D electronic or excitonic devices.