Graphene’s high mobility and Fermi velocity, combined with its constant light absorption in the visible to far-infrared range, make it an ideal material to fabricate high-speed and ultrabroadband ...photodetectors. However, the precise mechanism of photodetection is still debated. Here, we report wavelength and polarization-dependent measurements of metal–graphene–metal photodetectors. This allows us to quantify and control the relative contributions of both photothermo- and photoelectric effects, both adding to the overall photoresponse. This paves the way for a more efficient photodetector design for ultrafast operating speeds.
The combination of plasmonic nanoparticles and graphene enhances the responsivity and spectral selectivity of graphene-based photodetectors. However, the small area of the metal–graphene junction, ...where the induced electron–hole pairs separate, limits the photoactive region to submicron length scales. Here, we couple graphene with a plasmonic grating and exploit the resulting surface plasmon polaritons to deliver the collected photons to the junction region of a metal–graphene–metal photodetector. This gives a 400% enhancement of responsivity and a 1000% increase in photoactive length, combined with tunable spectral selectivity. The interference between surface plasmon polaritons and the incident wave introduces new functionalities, such as light flux attraction or repulsion from the contact edges, enabling the tailored design of the photodetector’s spectral response. This architecture can also be used for surface plasmon biosensing with direct-electric-redout, eliminating the need of bulky optics.
Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic and nanophotonic materials. The interaction of light with charge carriers creates an out-of-equilibrium ...distribution, which relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution, that subsequently cools emitting phonons. Although the slower relaxation mechanisms have been extensively investigated, the initial stages still pose a challenge. Experimentally, they defy the resolution of most pump-probe setups, due to the extremely fast sub-100 fs carrier dynamics. Theoretically, massless Dirac fermions represent a novel many-body problem, fundamentally different from Schrödinger fermions. Here we combine pump-probe spectroscopy with a microscopic theory to investigate electron-electron interactions during the early stages of relaxation. We identify the mechanisms controlling the ultrafast dynamics, in particular the role of collinear scattering. This gives rise to Auger processes, including charge multiplication, which is key in photovoltage generation and photodetectors.
We present here a characterization of the low background NaI(Tl) crystal NaI-33 based on a period of almost one year of data taking (891 kg
×
days exposure) in a detector configuration with no use of ...organic scintillator veto. This remarkably radio-pure crystal already showed a low background in the SABRE Proof-of-Principle (PoP) detector, in the low energy region of interest (1–6 keV) for the search of dark matter interaction via the annual modulation signature. As the vetoable background components, such as
40
K, are here sub-dominant, we reassembled the PoP setup with a fully passive shielding. We upgraded the selection of events based on a Boosted Decision Tree algorithm that rejects most of the PMT-induced noise while retaining scintillation signals with > 90% efficiency in 1–6 keV. We find an average background of 1.39 ± 0.02 counts/day/kg/keV in the region of interest and a spectrum consistent with data previously acquired in the PoP setup, where the external veto background suppression was in place. Our background model indicates that the dominant background component is due to decays of
210
Pb, only partly residing in the crystal itself. The other location of
210
Pb is the reflector foil that wraps the crystal. We now proceed to design the experimental setup for the physics phase of the SABRE North detector, based on an array of similar crystals, using a low radioactivity PTFE reflector and further improving the passive shielding strategy, in compliance with the new safety and environmental requirements of Laboratori Nazionali del Gran Sasso.
We report a versatile way of controlling the unsaturated loss, modulation depth and saturation fluence of graphene-based saturable absorbers (GSAs), by changing the thickness of a spacer between a ...single layer graphene (SLG) and a high-reflection mirror. This allows us to modulate the electric field intensity enhancement at the GSA from 0 up to 400%, due to the interference of incident and reflected light at the mirror. The unsaturated loss of the SLG-mirror-assembly can be reduced to ∼0. We use this to mode-lock a vertical-external-cavity surface-emitting laser (VECSEL) from 935 to 981 nm. This approach can be applied to integrate SLG into various optical components, such as output coupler mirrors, dispersive mirrors or dielectric coatings on gain materials. Conversely, it can also be used to increase the absorption (up to 10%) in various graphene based photonics and optoelectronics devices, such as photodetectors.
We present new results on the radiopurity of a 3.4-kg NaI(Tl) crystal scintillator operated in the SABRE proof-of-principle detector setup. The amount of potassium contamination, determined by the ...direct counting of radioactive 40K, is found to be 2.2 ± 1.5 ppb , lowest ever achieved for NaI(Tl) crystals. With the active veto, the average background rate in the crystal in the 1–6 keV energy region of interest (ROI) is 1.20 ± 0.05 counts / day / kg / keV , which is a breakthrough since the DAMA/LIBRA experiment. Our background model indicates that the rate is dominated by 210Pb and that about half of this contamination is located in the polytetrafluoroethylene reflector. We discuss ongoing developments of the crystal manufacture aimed at the further reduction of the background, including data from purification by zone refining. A projected background rate lower than ∼ 0.2 counts / day / kg / keV in the ROI is within reach. These results represent a benchmark for the development of next-generation NaI(Tl) detector arrays for the direct detection of dark matter particles.
Cercospora leaf spot (CLS) caused by
Cercospora beticola
occurs annually in Serbia causing severe yield losses of sugar beet, which requires intensive use of fungicides. In recent years we have ...observed unsatisfactory control of CLS originating from northwestern Serbia. Frequency of
C. beticola
populations resistant to Quinone outside inhibitors (QoI) was 81% (51/63 isolates), 98% (62/63) to sterol-demethylation inbibitors (DMI) and 54% (34/63) to methyl-2-benzimidazole carbamate fungicides (MBC). The genetic basis underlying the resistance was tested by characterizing the
cob
, CYP51 and ß-tubulin genes, associated with resistance to QoI, DMI and MBC fungicides, respectively. Isolates that were resistant to QoI fungicides had the G143A mutation in the
cob
gene. Characterization of the CYP51 gene revealed seven diverse haplotypes; however, no correlation with sensitivity or resistance to DMI fungicides could be identified. Resistance to MBC fungicides was associated with the presence of the E198A mutation in the ß-tubulin gene of all resistant isolates. From a total of 63 isolates originating from sugar beet fields of northwestern Serbia, 62 isolates showed resistance to multiple modes of action. Three multi-resistant phenotypes were identified: MR1 (
N
= 29) - resistant to QoI and DMI fungicides (QoI-R and DMI-R) but sensitive to MBC fungicides (MBC-S); MR2 (
N
= 11, QoI-S, DMI-R and MBC-R); and MR3 (
N
= 22), resistant to all three groups of fungicides (QoI-R, DMI-R and MBC-R). This is the first report of
C. beticola
resistance to QoI fungicides in Serbia. This study revealed development of multi-resistance of
C. beticola
isolates to MBC, DMI and QoI fungicides, which represents the first record of this phenomenon in
C. beticola
populations.
While pileups involving only two vehicles showcase obvious liability among the drivers, the assessment of liabilities is much more complex in chain collisions. In this work we propose an analytical ...indicator, named xEES, which easily allows to assess the correct liabilities among drivers. The name is mutated by the concept of energy equivalent speed (EES), which is the vehicle speed equivalent to the energy consumed to cause the vehicle deformation: xEES is indeed a dimensionless parameter related to the expected EES at the front of the first vehicle requested for a chain reaction car accident and that is energetically coherent with the damages of the hit vehicles. The proposed model needs only the information concerning the damages of the vehicles and does not require any information concerning the accident scene. The model has been tested on real pileups and validated by the software PC-Crash: the analysis has shown how the use of the coefficient xEES leads the engineer to assess the correct liabilities in pileups. Three intervals of variation are defined for xEES, which set apart, with due statistical confidence, chain reaction car accidents from collisions involving a column of moving vehicles.
•Indicator to assess the correct liabilities among drivers in Pileups.•xEES dimensionless parameter related to EES at the front of the first vehicle for a chain car accident.xEES is a dimensionless parameter related to the expected EES at the front of the first vehicle for a chain reaction car accident.•Three intervals that set apart chain reaction car accidents from collisions involving a column of moving vehicles.•Only the information concerning the damages of the vehicles (photos) are needed.•Tests on real life pileups and with the software Pc Crash.
We demonstrate a mid-infrared Raman-soliton continuum extending from 1.9 to 3 µm in a highly germanium-doped silica-clad fiber, pumped by a nanotube mode-locked thulium-doped fiber system, delivering ...12 kW sub-picosecond pulses at 1.95 µm. This simple and robust source of light covers a portion of the atmospheric transmission window.
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