Papers

Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV$^-$ triplet fluorescence. The absorption techniques rely on magnetic-field-dependent absorption at the NV$^-$ singlet zero phonon line at 1042$\,$nm and its phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050$\,$nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected magnetic resonance (ODMR) contrast. The highest contrast is found at 1042$\,$nm, but multiple points of high contrast are found at the peaks of the phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80$\,\%$ are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire phonon sideband. We determine the absorption cross section at 1042$\,$nm to be $\sigma^{\,\bigstar}_{1042}=(0.89\pm0.14)\cdot 10^{-21}\,\text{m}^2$ or $\sigma^{\,\blacktriangle}_{1042}=(2.9\pm0.5)\cdot 10^{-21}\,\text{m}^2$. depending on the employed 532$\,$nm NV$^-$ absorption cross section.

Organic scintillators have been used for decades to detect gamma rays or fast neutrons at low cost. Despite extensive efforts it is still difficult to combine stability, ruggedness, high light yield, and decent pulse-shape discrimination (PSD) in a single scintillator material. We took the unusual approach of embedding phosphors and wavelengths shifters in a solid polyurethane matrix, trying to combine the robustness of a common construction material with scintillating properties and PSD performance. The plastic scintillators resulting from years of research ultimately meet these intentions. Moreover, the production process is less demanding and less complex than that of conventional plastic scintillators. It allows to directly integrate light sensors or electronics into the scintillator. This opens the door for the construction of extremely compact and robust plastic detectors for the simultaneous detection of fast neutrons and gamma rays. This paper presents basic recipes and properties of scintillators based on this novel conception and discusses first applications in neutron imaging and personal radiation protection.