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Fiber-based mid-infrared (MIR) supercontinuum (SC) sources benefit from their spectral brightness and spatial coherence that are needed for many applications, such as spectroscopy and metrology. In this paper, an SC spanning from to is demonstrated in cascaded ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) and As2Se3 step-index fibers. The pump source is a ZBLAN fiber-based MIR SC laser with abundant high-peak-power soliton pulses between 3000 nm and 4200 nm. By concatenating the ZBLAN fiber and the As2Se3 fiber, efficient cascading red-shifts are obtained in the normal dispersion region of the As2Se3 fiber. The spectral behavior of cascaded SC generation shows that the long-wavelength proportion of MIR SC generated in the ZBLAN fiber plays a critical role for further spectral extension in the As2Se3 fiber. [ABSTRACT FROM AUTHOR]

Inorganic scintillators are widely used for fast timing applications in high-energy physics (HEP) experiments, time-of-flight positron emission tomography and time tagging of soft and hard x-ray photons at advanced light sources. As the best coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation decay time it is worth studying fast cross-luminescence, for example in BaF2 which has an intrinsic yield of about 1400 photons/MeV. However, emission bands in BaF2 are located in the deep-UV at 195 nm and 220 nm, which sets severe constraints on photodetector selection. Recent developments in dark matter and neutrinoless double beta decay searches have led to silicon photomultipliers (SiPMs) with photon detection efficiencies of 20%–25% at wavelengths of 200 nm. We tested state-of-the-art devices from Fondazione Bruno Kessler and measured a best CTR of 51 ± 5 ps full width at half maximum when coupling 2 mm × 2 mm × 3 mm BaF2 crystals excited by 511 keV electron–positron annihilation gammas. Using these vacuum ultraviolet SiPMs we recorded the scintillation kinetics of samples from Epic Crystal under 511 keV excitation, confirming a fast decay time of 855 ps with 12.2% relative light yield and 805 ns with 84.0% abundance, together with a smaller rise time of 4 ps beyond the resolution of our setup. The total intrinsic light yield was determined to be 8500 photons/MeV. We also revealed a faster component with 136 ps decay time and 3.7% light yield contribution, which is extremely interesting for the fastest timing applications. Timing characteristics and CTR results on BaF2 samples from different producers and with different dopants (yttrium, cadmium and lanthanum) are given, and clearly show that the the slow 800 ns emission can be effectively suppressed. Such results ultimately pave the way for high-rate ultrafast timing applications in medical diagnosis, range monitoring in proton or heavy ion therapy and HEP. [ABSTRACT FROM AUTHOR]

Magneto-optical trapping (MOT) is a key technique on the route towards ultracold molecular ensembles. However, the realization and optimization of magneto-optical traps with their wide parameter space is particularly difficult. Here, we present a very general method for the optimization of molecular magneto-optical trap operation by means of Bayesian optimization. As an example for a possible application, we consider the optimization of a calcium fluoride MOT for maximum capture velocity. We find that both the X2Σ+ to A2Π1/2 and the X2Σ+ to B2Σ+ transition to allow for capture velocities with 24 m s−1 and 23 m s−1 respectively at a total laser power of 200 mW. In our simulation, the optimized capture velocity depends logarithmically on the beam power within the simulated power range of 25 to 400 mW. Applied to heavy molecules such as BaH, BaF, YbF and YbOH with their low capture velocity MOTs it might offer a route to far more robust MOT. [ABSTRACT FROM AUTHOR]

BaF is one of the potential candidates for the experimental search of the electric dipole moment of the electron (eEDM). The NL-eEDM collaboration is building a new experimental set up to measure the eEDM using the BaF molecule (The NL-eEDM collaboration, 2018 Eur. Phys. J. D 72 : 197). To analyze the results of such an experiment, one would require the accurate value of the molecular -odd interaction parameters that cannot be measured from any experiment. In this work, we report the precise value of the -odd interaction parameters of the BaF molecule obtained from the four-component relativistic coupled-cluster calculations. We also calculate the hyperfine structure (HFS) constants of the same molecule to assess the reliability of the reported molecular parameters. The calculated HFS constants show good agreement with the available experimental values. Further, the systematic effects of electron-correlation along with the roles of inner-core electrons and the virtual energy functions in the calculation of the studied properties of BaF are investigated. [ABSTRACT FROM AUTHOR]

Solid state photodetectors like silicon photomultipliers (SiPMs) are playing an important role in several fields of medical imaging, life sciences and high energy physics. They are able to sense optical photons with a single photon detection time precision below 100 ps, making them ideal candidates to read the photons generated by fast scintillators in time of flight positron emission tomography (TOF-PET). By implementing novel high-frequency readout electronics, it is possible to perform a completely new evaluation of the best timing performance achievable with state-of-the-art analog-SiPMs and scintillation materials. The intrinsic SiPM single photon time resolution (SPTR) was measured with Ketek, HPK, FBK, SensL and Broadcom devices. Also, the best achieved coincidence time resolution (CTR) for these devices was measured with LSO:Ce:Ca of mm3 and mm3 size crystals. The intrinsic SPTR for all devices ranges between 70 ps and 135 ps FWHM when illuminating the entire mm2 or mm2 area. The obtained CTR with LSO:Ce:Ca of mm3 size ranges between 58 ps and 76 ps FWHM for the SiPMs evaluated. Bismuth Germanate (BGO), read out with state of-the-art NUV-HD SiPMs from FBK, achieved a CTR of 158 ps and 277 ps FWHM for mm3 and mm3 crystals, respectively. Other BGO geometries yielded 167 3 ps FWHM for mm3 and 235 5 ps FWHM for mm3 also coupled with Meltmount (n = 1.582) and wrapped in Teflon. Additionally, the average number of Cherenkov photons produced by BGO in each 511 keV event was measured to be 17 3 photons. Based on this measurement, we predict the limits of BGO for ultrafast timing in TOF-PET with Monte Carlo simulations. Plastic scintillators (BC422, BC418), BaF2, GAGG:Ce codoped with Mg and CsI:undoped were also tested for TOF performance. Indeed, BC422 can achieve a CTR of 35 2 ps FWHM using only Compton interactions in the detector with a maximum deposited energy of 340 keV. BaF2 with its fast cross-luminescence enables a CTR of 51 5 ps FWHM when coupled to VUV-HD SiPMs from FBK, with only ∼22% photon detection efficiency (PDE). We summarize the measured CTR of the various scintillators and discuss their intrinsic timing performance. [ABSTRACT FROM AUTHOR]

In this work, we report a novel approach to the surface nanostructuring of lead tin telluride films using inductively coupled argon plasma treatment with the average ion energy of 200 eV and the duration of 20–60 s. The nanostructuring was carried out on the plasma treated surface of epitaxial single-crystal Pb1−xSnxTe films grown on BaF2(111) substrates using molecular beam epitaxy. The plasma treatment of the surface of the Pb1−xSnxTe films with the low and medium Sn content (x = 0–0.6) resulted in the formation of the arrays of 'capped' conical nanostructures with the height up to 420 nm, depending on the Sn content and treatment duration, and the surface density of ∼109 cm−2. The plasma treatment of the surface of the films with the high Sn content (x = 0.8–1) yielded the formation of a second group of flat nanostructures without 'caps', which had necklace-like rings consisting of multiple nanodroplets around their rims. Using transmission electron microscopy, we show that the quasi-spherical droplet 'caps' of the nanostructures consist of Pb 'wrapped' in Sn. We explain the physical mechanism of the observed plasma-assisted nanostructure self-formation in the framework of the multi-stage model including physical sputtering, redeposition, vapour-liquid-solid mechanism and micromasking mechanism. [ABSTRACT FROM AUTHOR]