First Probe of Sub-GeV Dark Matter beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS.

The COHERENT Collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220  MeV/c^{2} using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9  keV_{nr}. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei.

Nonlinear Optical Signal Generation Mediated by a Plasmonic Azimuthally Chirped Grating.

Plasmonic gratings are simple and effective platforms for nonlinear signal generation since they provide a well-defined momentum for photon-plasmon coupling and local hot spots for frequency conversion. Here, a plasmonic azimuthally chirped grating (ACG), which provides spatially resolved broadband momentum for photon-plasmon coupling, was exploited to investigate the plasmonic enhancement effect in two nonlinear optical processes, namely two-photon photoluminescence (TPPL) and second harmonic generation (SHG). The spatial distributions of the nonlinear signals were determined experimentally by hyperspectral mapping with ultrashort pulsed excitation.

Measurement of the Coherent Elastic Neutrino-Nucleus Scattering Cross Section on CsI by COHERENT.

We measured the cross section of coherent elastic neutrino-nucleus scattering (CEvNS) using a CsI[Na] scintillating crystal in a high flux of neutrinos produced at the Spallation Neutron Source at Oak Ridge National Laboratory. New data collected before detector decommissioning have more than doubled the dataset since the first observation of CEvNS, achieved with this detector. Systematic uncertainties have also been reduced with an updated quenching model, allowing for improved precision.

First Measurement of Coherent Elastic Neutrino-Nucleus Scattering on Argon.

We report the first measurement of coherent elastic neutrino-nucleus scattering (CEvNS) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer CEvNS over the background-only null hypothesis with greater than 3σ significance. The measured cross section, averaged over the incident neutrino flux, is (2.

Spatially Resolving the Enhancement Effect in Surface-Enhanced Coherent Anti-Stokes Raman Scattering by Plasmonic Doppler Gratings.

Well-designed plasmonic nanostructures can mediate far and near optical fields and thereby enhance light-matter interactions. To obtain the best overall enhancement, structural parameters need to be carefully tuned to obtain the largest enhancement at the input and output frequencies. This is, however, challenging for nonlinear light-matter interactions involving multiple frequencies because obtaining the full picture of structure-dependent enhancement at individual frequencies is not easy.