Selection rules for the orbital angular momentum of optically produced THz radiation

In this work, we theoretically study the transduction of orbital angular momentum (OAM) l for infrared pump lasers into the THz domain. In the case of optical rectification, the transduction of OAM occurs only through a spin-orbit interaction, with the selection rule on the OAM l=0 valid for any kind of polarization of the pump, which means that there is no transfer of OAM along the propagation axis. In difference frequency generation, the selection rule for the difference Δl between the OAM of the pump fields with linear or circular polarization is l=Δl, whereas l ranges from Δl-2 to Δl+2 in cases of both radial and azimuthal polarization. Moreover, for THz generation in the latter case, the high diffraction obtained with tightly focused pumps yields l tending to Δl±2, while l tends to zero in the opposite case of large pump beams.

A cryogenic magneto-optical device for long wavelength radiation

We present here a small-scale liquid helium immersion cryostat with an innovative optical setup suitable to work in long wavelength radiation ranges and under an applied magnetic field. The cryostat is a multi-stage device with several shielding in addition to several optical stages. The system has been designed with an external liquid nitrogen boiler to reduce liquid bubbling. The optical and mechanical properties of the optical elements were calculated and optimized for the designed configuration, while the optical layout has been simulated and optimized among different configurations based on the geometry of the device. The final design has been optimized for low-noise radiation measurements of proximity junction arrays under an applied magnetic field in the wavelength range λ = 250 μm-2500 μm.

Terahertz Tuning of Dirac Plasmons in Bi_{2}Se_{3} Topological Insulator

Light can be strongly confined in subwavelength spatial regions through the interaction with plasmons, the collective electronic modes appearing in metals and semiconductors. This confinement, which is particularly important in the terahertz spectral region, amplifies light-matter interaction and provides a powerful mechanism for efficiently generating nonlinear optical phenomena. These effects are particularly relevant in graphene and topological insulators, where massless Dirac fermions show a naturally nonlinear optical behavior in the terahertz range. The strong interaction scenario has been considered so far from the point of view of light. In this Letter, we investigate instead the effect of strong interaction on the plasmon itself. In particular, we will show that Dirac plasmons in Bi_{2}Se_{3} topological insulator are strongly renormalized when excited by high-intensity terahertz radiation by displaying a huge red-shift down to 60% of its characteristic frequency. This opens the road towards tunable terahertz nonlinear optical devices based on topological insulators.

Terahertz-based retrieval of the spectral phase and amplitude of ultrashort laser pulses

Terahertz (THz) radiation is of great interest for a variety of applications, e.g., particle accelerations, spectroscopy investigations of quantum systems, and high-field study of materials. One of the most common laser-based processes to produce THz pulses is optical rectification, which transduces an infrared pump laser to the THz domain (0.1-20 THz). In this work, we propose and theoretically describe a method to characterize the amplitude and phase of the electric field of the pump laser pulse relying on THz generation and detection. We demonstrate with a numerical example how THz radiation can be used as diagnostics to characterize laser pulses with temporal length at the femtosecond level.

Resonant plasma excitation by single-cycle THz pulses

In this paper, an alternative perspective for the generation of millimetric high-gradient resonant plasma waves is discussed. This method is based on the plasma-wave excitation by energetic single-cycle THz pulses whose temporal length is comparable to the plasma wavelength. The excitation regime discussed in this paper is the quasi-nonlinear regime that can be achieved when the normalized vector potential of the driving THz pulse is on the order of unity. To investigate this regime and determine the strength of the excited electric fields, a Particle-In-Cell (PIC) code has been used. It has been found that by exploiting THz pulses with characteristics currently available in laboratory, longitudinal electron plasma waves with electric gradients up to hundreds MV/m can be obtained. The mm-size nature of the resonant plasma wave can be of great utility for an acceleration scheme in which high-brightness electron bunches are injected into the wave to undergo a strong acceleration. The long-size nature of the acceleration bucket with respect to the short length of the electron bunches can be handled in a more robust manner in comparison with the case when micrometric waves are employed.

Orbital dependent coherence temperature and optical anisotropy of V2O3 quasiparticles

We report on an orbital and temperature dependent study of the onset of coherent quasiparticles in V₂O₃ single crystal. By using polarized infrared spectroscopy we demonstrate that the electronic coherence temperature is strongly orbital dependent, being about 400 K for [Formula: see text] orbitals and 500 K for the [Formula: see text]. This suggests that V₂O₃ low energy electrodynamics can be described in terms of two electron liquids differently renormalized by electronic correlations.

Mottness at finite doping and charge-instabilities in cuprates

The influence of the Mott physics on the doping-temperature phase diagram of copper oxides represents a major issue that is subject of intense theoretical and experimental effort. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p→Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal. This reorganization of the high-energy degrees of freedom occurs at the critical doping p_cr ≈0.16 irrespective of the temperature, and it can be well described by dynamical mean field theory calculations. We argue that the onset of the low-temperature charge instabilities is the low-energy manifestation of the underlying Mottness that characterizes the p < p_cr region of the phase diagram. This discovery sets a new framework for theories of charge order and low-temperature phases in underdoped copper oxides.

Knowledge and behaviour of nursing students on the prevention of healthcare associated infections

INTRODUCTION

Hospital infections, or "healthcare associated infections" (HAI) represent the most common and serious complications of healthcare. Adoption of safe care practices able to prevent or control the transmission of infections, both in hospitals and in other healthcare settings is crucial. The aim of the study is to assess the awareness about the risk factors and the most effective measures of prevention of HAI in the University of Ferrara nursing school students, giving particular attention to the hand hygiene practices and the use of standard precautions.

METHODS

339 students attending all the three years of course of the same academic year were enrolled. An anonymous questionnaire was administered in order to investigate the knowledge about three specific areas: infections associated with healthcare practices (HAI), standard precautions (SP) and hand hygiene (HH).

RESULTS

A sufficient level of knowledge by all the three groups of students was observed only in the SP area. A barely sufficient score was reached only by the third year students with regard to the proper HH. The level of knowledge about HAI was inadequate.

CONCLUSIONS

A periodically check of nursing students' knowledge would be advisable in order to fill any gaps, improve training, reduce HAI and increase prevention measures compliance.

Terahertz plasmonic excitations in Bi2Se3 topological insulator

After the discovery of Dirac electrons in condensed matter physics, more specifically in graphene and its derivatives, their potentialities in the fields of plasmonics and photonics have been readily recognized, leading to a plethora of applications in active and tunable optical devices. Massless Dirac carriers have been further found in three-dimensional topological insulators. These exotic quantum systems have an insulating gap in the bulk and intrinsic Dirac metallic states at any surface, sustaining not only single-particle excitations but also plasmonic collective modes. In this paper we will review the plasmon excitations in different microstructures patterned on Bi₂Se₃ topological insulator thin films as measured by terahertz spectroscopy. We discuss the dependence of the plasmon absorption versus the microstructure shape, wavevector, and magnetic field. Finally we will discuss the topological protection of both the Dirac single-particle and plasmon excitations.

Efficacy of ultrasound-guided transversus abdominis plane block in laparoscopic hysterectomy. Clinical trial

OBJECTIVES

Transversus abdominis plane block is a regional anaesthesia technique that has proven to be effective for postoperative pain reduction in different abdominal surgical procedures. This study evaluated its efficacy on post laparoscopic hysterectomy pain intensity and analgesic consumption.

MATERIALS AND METHODS

Randomized controlled trial which included 40 patients scheduled for laparoscopic hysterectomy, enrolled in 2 groups: transversus abdominis plane block+systemic analgesia (Group 1; n=20), versus systemic analgesia (Group 2; n=20). Opioid consumption within the first 24 postoperative hours, pain intensity scores at 60min, 2, 8 and 24h after surgery, adverse events related to systemic analgesia and time to hospital discharge were evaluated and registered.

RESULTS

We found no differences between both groups in opioid consumption (10mg vs. 7mg; P=.2) and pain scores (NVS) within the first 24 postoperative hours, at 60min (3 vs. 5; P=.65), 120min (0 vs. 2; P=.15), 8 and 24h (0 vs. 0; P>.50) for the last 2 points in time analysed. Adverse events related to medication and time to hospital discharge showed similar results.

CONCLUSIONS

Adding a transversus abdominis plane block technique to opioid PCA does not seem to improve postoperative pain management in laparoscopic hysterectomy. Patient preparation time and costs could be incremented and complications (although rare) related to the technique could appear.

Fermi Surface of Metallic V_{2}O_{3} from Angle-Resolved Photoemission: Mid-level Filling of e_{g}^{π} Bands

Using angle resolved photoemission spectroscopy, we report the first band dispersions and distinct features of the bulk Fermi surface (FS) in the paramagnetic metallic phase of the prototypical metal-insulator transition material V_{2}O_{3}. Along the c axis we observe both an electron pocket and a triangular holelike FS topology, showing that both V 3d a_{1g} and e_{g}^{π} states contribute to the FS. These results challenge the existing correlation-enhanced crystal field splitting theoretical explanation for the transition mechanism and pave the way for the solution of this mystery.

Surface Effects on the Mott-Hubbard Transition in Archetypal V{2}O{3}

We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V{2}O{3}. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations.

Spectral Weight Redistribution in (LaNiO3)n/(LaMnO3)2 Superlattices from Optical Spectroscopy

We have studied the optical properties of four (LaNiO3)n/(LaMnO3)2 superlattices (SL) (n=2,3,4,5) on SrTiO3 substrates. We have measured the reflectivity at temperatures from 20 to 400 K, and extracted the optical conductivity through a fitting procedure based on a Kramers-Kronig consistent Lorentz-Drude model. With increasing LaNiO3 thickness, the SLs undergo an insulator-to-metal transition (IMT) that is accompanied by the transfer of spectral weight from high to low frequency. The presence of a broad midinfrared band, however, shows that the optical conductivity of the (LaNiO3)n/(LaMnO3)2 SLs is not a linear combination of the LaMnO_{3} and LaNiO3 conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites.

Optical properties of a vibrationally modulated solid state Mott insulator

Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode.

Infrared evidence of a Slater metal-insulator transition in NaOsO₃

The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO₃ 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO₃ is the first known 3D Slater insulator.

Observation of Dirac plasmons in a topological insulator

Plasmons are quantized collective oscillations of electrons and have been observed in metals and doped semiconductors. The plasmons of ordinary, massive electrons have been the basic ingredients of research in plasmonics and in optical metamaterials for a long time. However, plasmons of massless Dirac electrons have only recently been observed in graphene, a purely two-dimensional electron system. Their properties are promising for novel tunable plasmonic metamaterials in the terahertz and mid-infrared frequency range. Dirac fermions also occur in the two-dimensional electron gas that forms at the surface of topological insulators as a result of the strong spin-orbit interaction existing in the insulating bulk phase. One may therefore look for their collective excitations using infrared spectroscopy. Here we report the first experimental evidence of plasmonic excitations in a topological insulator (Bi2Se3). The material was prepared in thin micro-ribbon arrays of different widths W and periods 2W to select suitable values of the plasmon wavevector k. The linewidth of the plasmon was found to remain nearly constant at temperatures between 6 K and 300 K, as expected when exciting topological carriers. Moreover, by changing W and measuring the plasmon frequency in the terahertz range versus k we show, without using any fitting parameter, that the dispersion curve agrees quantitatively with that predicted for Dirac plasmons.

The TeraFERMI terahertz source at the seeded FERMI free-electron-laser facility

We describe the project for the construction of a terahertz (THz) beamline to be called TeraFERMI at the seeded FERMI free electron laser (FEL) facility in Trieste, Italy. We discuss topics as the underlying scientific case, the choice of the source, the expected performance, and THz beam propagation. Through electron beam dynamics simulations we show that the installation of the THz source in the beam dump section provides a new approach for compressing the electron bunch length without affecting FEL operation. Thanks to this further compression of the FEL electron bunch, the TeraFERMI facility is expected to provide THz pulses with energies up to the mJ range during normal FEL operation.

Characterization of the THz radiation source at the Frascati linear accelerator

The linac driven coherent THz radiation source at the SPARC-LAB test facility is able to deliver broadband THz pulses with femtosecond shaping. In addition, high peak power, narrow spectral bandwidth THz radiation can be also generated, taking advantage of advanced electron beam manipulation techniques, able to generate an adjustable train of electron bunches with a sub-picosecond length and with sub-picosecond spacing. The paper reports on the manipulation, characterization, and transport of the electron beam in the bending line transporting the beam down to the THz station, where different coherent transition radiation spectra have been measured and studied with the aim to optimize the THz radiation performances.

Optical conductivity measurements of GaTa4Se8 under high pressure: evidence of a bandwidth-controlled insulator-to-metal Mott transition

The optical properties of a GaTa(4)Se(8) single crystal are investigated under high pressure. At ambient pressure, the optical conductivity exhibits a charge gap of ≈0.12 eV and a broad midinfrared band at ≈0.55 eV. As pressure is increased, the low energy spectral weight is strongly enhanced and the optical gap is rapidly filled, pointing to an insulator to metal transition around 6 GPa. The overall evolution of the optical conductivity demonstrates that GaTa(4)Se(8) is a Mott insulator which undergoes a bandwidth-controlled Mott metal-insulator transition under pressure, in remarkably good agreement with theory. With the use of our optical data and ab initio band structure calculations, our results were successfully compared to the (U/D, T/D) phase diagram predicted by dynamical mean field theory for strongly correlated systems.

Vibrational spectrum of solid picene (C22H14)

Recently, Mitsuhashi et al observed superconductivity with a transition temperature up to 18 K in potassium doped picene (C(22)H(14)), a polycyclic aromatic hydrocarbon compound (Mitsuhashi et al 2010 Nature 464 76). Theoretical analysis indicates the importance of electron-phonon coupling in the superconducting mechanisms of these systems, with different emphasis on inter- and intra-molecular vibrations, depending on the approximations used. Here we present a combined experimental and ab initio study of the Raman and infrared spectrum of undoped solid picene, which allows us to unambiguously assign the vibrational modes. This combined study enables the identification of the modes which couple strongly to electrons and hence can play an important role in the superconducting properties of the doped samples.