Spontaneous Raman spectroscopy is a powerful characterization tool for graphene research. Its extension to the coherent regime, despite the large nonlinear third-order susceptibility of graphene, has ...so far proven challenging. Due to its gapless nature, several interfering electronic and phononic transitions concur to generate its optical response, preventing to retrieve spectral profiles analogous to those of spontaneous Raman. Here we report stimulated Raman spectroscopy of the G-phonon in single and multi-layer graphene, through coherent anti-Stokes Raman Scattering. The nonlinear signal is dominated by a vibrationally non-resonant background, obscuring the Raman lineshape. We demonstrate that the vibrationally resonant coherent anti-Stokes Raman Scattering peak can be measured by reducing the temporal overlap of the laser excitation pulses, suppressing the vibrationally non-resonant background. We model the spectra, taking into account the electronically resonant nature of both. We show how coherent anti-Stokes Raman Scattering can be used for graphene imaging with vibrational sensitivity.
Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular phenomena, including metal-insulator transitions, superconductivity and subpicosecond ...modification of magnetic order. The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, Eex , is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photo-induced dynamics of magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to Eex . By unravelling the photo-induced modification of the two-magnon line frequency from a dominating nonlinear optical effect, we find that Eex is increased by the electromagnetic stimulus.
We introduce a general theoretical description of non resonant impulsive femtosecond stimulated Raman spectroscopy in a multimode harmonic model. In this technique an ultrashort actinic pulse creates ...coherences of low frequency modes and is followed by a paired narrowband Raman pulse and a broadband probe pulse. Using closed-time-path-loop (CTPL) diagrams, the response on both the red and the blue sides of the broadband pulse with respect to the narrowband Raman pulse is calculated, the process couples high and low frequency modes, which share the same ground state. The transmitted intensity oscillates between the red and the blue side, while the total number of photons is conserved. The total energy of the probe signal is periodically modulated in time by the coherence created in the low frequency modes.
Spontaneous Raman spectroscopy is a formidable tool to probe molecular vibrations. Under electronic resonance conditions, the cross section can be selectively enhanced enabling structural sensitivity ...to specific chromophores and reaction centers. The addition of an ultrashort, broadband femtosecond pulse to the excitation field allows for coherent stimulation of diverse molecular vibrations. Within such a scheme, vibrational spectra are engraved onto a highly directional field, and can be heterodyne detected overwhelming fluorescence and other incoherent signals. At variance with spontaneous resonance Raman, however, interpreting the spectral information is not straightforward, due to the manifold of field interactions concurring to the third order nonlinear response. Taking as an example vibrational spectra of heme proteins excited in the Soret band, we introduce a general approach to extract the stimulated Raman excitation profiles from complex spectral lineshapes. Specifically, by a quantum treatment of the matter through density matrix description of the third order nonlinear polarization, we identify the contributions which generate the Raman bands, by taking into account for the cross section of each process.
Spontaneous Raman is a well‐established tool to probe molecular vibrations. Under resonant conditions, it is a largely used method for characterizing the structure of heme‐proteins. In recent years, ...advances in pulsed laser sources allowed to explore vibrational features with complex techniques based on nonlinear optical interactions, among which is stimulated Raman scattering (SRS). Building on its combined spectral–temporal resolutions and high chemical sensitivities, SRS has been largely applied as a probe for ultrafast, time‐resolved studies, as well as an imaging technique in biological systems. By using a frequency tunable, narrowband pump pulse jointly with a femtosecond white light continuum to initiate the SRS process, here we measure the Raman spectrum of a prototypical heme‐protein, namely deoxy myoglobin, under two different electronic resonances. The SRS results are compared with the spontaneous Raman spectra, and the relative advantages, such as the capability of our experimental approach to provide an accurate mapping of Raman excitation profiles, are discussed.
Combining a frequency tunable, narrowband pump pulse, and a femtosecond white light continuum, the stimulated Raman spectrum of a prototypical heme‐protein, namely, deoxymyoglobin, is measured under two different resonance conditions. Comparison with spontaneous resonant Raman is discussed.
Performance of the Belle II Silicon Vertex Detector Tanigawa, H.; Adamczyk, K.; Aihara, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2020, Letnik:
972
Journal Article
Recenzirano
The Belle II experiment at the SuperKEKB collider of KEK (Japan) started recording physics data in spring 2019 with all its subdetectors installed and with the goal of accumulating 50ab−1 of e+e− ...collision events at the unprecedented instantaneous luminosity of 8×1035cm−2s−1, about 40 times larger than its predecessor. The Belle II vertex detector plays a crucial role in the broad Belle II physics program, especially for time-dependent CP measurements. It consists of two layers of DEPFET-based pixels and four layers of double-sided silicon strip detectors (SVD).
The experience gained from the first period of SVD operation can be summarized as smooth and reliable running of the detector, with high stability of noise levels and calibration parameters obtained from local calibration runs. No major problem has been experienced. The detector even survived a few serious radiation accidents in which the beam was lost due to failure in the machine focusing quadrupoles without any notable damage. The SVD performance were carefully studied with these first physics data. The SVD showed excellent hit and tracking efficiency. Moreover, cluster energy and signal to noise ratio as well as the hit time and spatial resolutions measured on data showed a fair agreement with the expected performance.
•Belle II silicon vertex detector operated during the first year of the experiment.•All sensors worked with stable and excellent hit efficiencies above 99 %.•Signal-to-noise ratios between 15 and 30, cluster time resolution better than 3 ns.•First effects of irradiation visible in leakage currents.
Abstract
The Extreme Energy Events experiment (EEE) is a cosmic ray observatory made of about 60 muon telescopes based on Multigap Resistive Plate Chamber (MRPC) detectors. The EEE experiment has two ...main targets: a scientific and a dissemination. The EEE collaboration has also developed a large set of portable scintillator-based detectors, named Cosmic Box (CB), mainly used for educational purposes. The CB allows students to perform cosmic ray counting measurements in several environments. CBs are made of two 15 × 15 × 1 cm scintillators read by two 3 × 3 mm
2
SiPMs operated in coincidence. Three CBs were deployed in Nuraxi Figus and Seruci coal mine to perform an underground measurement of the cosmic muon flux attenuation. High school and university students were directly involved in all the stages of the measurements: from the preliminary measurements to the on-site work and data analysis.
Cosmic ray muons are a penetrating component of extensive air showers created in the Earth atmosphere by the interaction of highly energetic primary particles, mostly protons, which continuously ...bombard our Planet. The secondary cosmic radiation is the result of the complex interplay between the production cross section and the interaction mechanisms with the atmosphere (including the energy loss, multiple scattering and particle decay). Cosmic muons have been considered since several decades as a powerful probe to exploit our environment, from muography of volcanoes to absorption radiography of possible hidden rooms inside large structures, such as Pyramids, to the detection of high-Z illicit nuclear materials inside containers and many other applications of social interest. This paper discusses the possibility to employ the Multigap Resistive Plate Chambers (MRPC) of the Extreme Energy Events (EEE) Project as muon tracking detectors to monitor the long term stability of civil buildings and structures when used in conjunction with additional detectors. For this application the average direction of the cosmic muon tracks passing through the MRPC telescope and an additional detector located some distance apart in the same building may be reconstructed with good precision and any small variation over long time acquisition periods may be monitored. The performance of such setup is discussed and experimental results from first coincidence measurements obtained with a 40 × 60 cm2 scintillator detector operated in the same building with one of the EEE telescopes, at about 15 m vertical distance from it, are presented. Simple Monte Carlo and GEANT simulations were also carried out to evaluate typical acceptance values for the operating conditions employed so far, to extrapolate to other geometrical configurations, and to evaluate multiple scattering effects.
The Extreme Energy Events (EEE) Project is an experiment aimed at the detection of secondary cosmic ray muons. It consists of a sparse array of about 60 telescopes, based on Multigap Resistive Plate ...Chambers (MRPCs), mostly distributed throughout the Italian territory, mainly in high schools locations, and at CERN. The telescopes are now operational and taking data since more than ten years with a high duty cycle and detection efficiency. The analysis activity is currently in progress and focused on several items, including the detailed study of the muon ux under dfferent conditions, its connection with atmospheric and solar events, the detection of extensive air showers and the search for long distance correlations between different extensive air showers. In this paper an overall description of the experiment will be given, together with its educational fallout. The operation of the whole array is also discussed by showing the most recent results obtained from the analysis of the collected data.
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