Immunity of intersubband polaritons to inhomogeneous broadening

We demonstrate that intersubband (ISB) polaritons are robust to inhomogeneous effects originating from the presence of multiple quantum wells (MQWs). In a series of samples that exhibit mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 meV to 20meV), we have observed polariton linewidths always lying in the 4 - 7 meV range only. We have experimentally verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction effect of the polariton modes persists up to room-temperature. This immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode. It is a precious tool to gauge the natural linewidth of the ISB plasmon , that is otherwise masked in such MQWs system , and is also beneficial in view of perspective applications such as intersubband polariton lasers

Source parameters of moderate-to-large Chinese earthquakes from the time evolution of P-wave peak displacement on strong motion recordings

In this work we propose and apply a straightforward methodology for the automatic characterization of the extended earthquake source, based on the progressive measurement of the P-wave displacement amplitude at the available stations deployed around the source. Specifically, we averaged the P-wave peak displacement measurements among all the available stations and corrected the observed amplitude for distance attenuation effect to build the logarithm of amplitude vs. time function, named LPDT curve. The curves have an exponential growth shape, with an initial increase and a final plateau level. By analyzing and modelling the LPDT curves, the information about earthquake rupture process and earthquake magnitude can be obtained. We applied this method to the Chinese strong motion data from 2007 to 2015 with Ms ranging between 4 and 8. We used a refined model to reproduce the shape of the curves and different source models based on magnitude to infer the source-related parameters for the study dataset. Our study shows that the plateau level of LPDT curves has a clear scaling with magnitude, with no saturation effect for large events. By assuming a rupture velocity of 0.9 Vs, we found a consistent self-similar, constant stress drop scaling law for earthquakes in China with stress drop mainly distributed at a lower level (0.2 MPa) and a higher level (3.7 MPa). The derived relation between the magnitude and rupture length may be feasible for real-time applications of Earthquake Early Warning systems

Contraction of cross-linked actomyosin bundles

Cross-linked actomyosin bundles retract when severed in vivo by laser ablation, or when isolated from the cell and micromanipulated in vitro in the presence of ATP. We identify the time scale for contraction as a viscoelastic time tau, where the viscosity is due to (internal) protein friction. We obtain an estimate of the order of magnitude of the contraction time tau ~ 10-100 s, consistent with available experimental data for circumferential microfilament bundles and stress fibers. Our results are supported by an exactly solvable, hydrodynamic model of a retracting bundle as a cylinder of isotropic, active matter, from which the order of magnitude of the active stress is estimated.Comment: To be published in Physical Biolog

Crestal or 1.5 Mm Subcrestal Positioning of Transmucosal Dental Implants with Cemented or Screw-retained Crowns in Posterior Jaws: 4-month Data from a Single Centre Randomised Controlled Trial

OBJECTIVES. To compare crestal versus 1.5 mm subcrestal positioning of single transmu-cosal dental implants and screw-retained versus cemented crowns. MATERIALS AND METHODS. One hundred and sixty partially edentulous patients requiring one single implant-supported crown in the premolar/molar area were randomly allocated to four arms: crestal positioning and screw-retained crown (Group 1, 40 patients); crestal positioning and cement-retained crown (Group 2, 40 patients); 1.5 mm subcrestal positioning and screw-retained crown (Group 3, 40 patients); or 1.5 mm subcrestal positioning and cement-retained crown (Group 4, 40 patients) by a single operator. After an unloaded healing period of 3 months, definitive metal-ceramic crowns were delivered, and patients were followed up to 4 months after loading. Outcome measures were: crown and implant failures, complications, aesthetics assessed using the pink aesthetic score (PES), peri-implant marginal bone level changes and patient satisfaction, all recorded, when possible, by blinded assessors. RESULTS. At four months post-loading, four patients dropped out (two from Group 1 and one each from Groups 2 and 3, respectively). Two implants each failed in Groups 2 and 4, but there were no statistically significant differences between groups (P = 1.000). Complications affected four patients from Group 1, one from Group 2, two from Group 3 and six from Group 4, but between-group differences were not statistically significant (P = 0.207). The mean pink aesthetic scores were 10.30 ± 2.13 (Group 1), 10.22 ± 2.76 (Group 2), 10.47 ± 2.96 (Group 3), and 10.51 ± 2.24 (Group 4), respectively, with no statistically significant differences between groups (P = 0.9541). Likewise, there were no statistically significant differences in peri-implant marginal bone loss at 4 months after loading between groups (P = 0.9011:-0.21 mm ± 0.28 for Group 1,-0.25 mm ± 0.27 for Group 2,-0.28 mm ± 0.57 for Group 3 and-0.24 mm ± 0.26 for Group 4). Furthermore, there were no differences in patient satisfaction in terms of either function (P = 0.400) or aesthetics (P = 1.000), and all patients would undergo the same intervention again. CONCLUSIONS. No appreciable statistical or clinical differences were found between cre-stal or 1.5 mm subcrestal placement of transmucosal implants in posterior jaws or between rehabilitation with screw-retained or cement-retained crowns. However, longer follow-ups are required in order to formulate reliable clinical recommendations. CONFLICT OF INTEREST STATEMENT. GlobalD (Brignais, France), the manufacturer of the implants used in this investigation, partially funded this trial and donated the implants and the prosthetic components. However, all data belongs to the authors and the sponsor by no means interfered with the conduct of the trial or the publication of its results

Theory of coherent optical nonlinearities of intersubband transitions in semiconductor quantum wells

We theoretically study the coherent nonlinear response of electrons confined in semiconductor quantum wells under the effect of an electromagnetic radiation close to resonance with an intersubband transition. Our approach is based on the time-dependent Schr\"odinger-Poisson equation stemming from a Hartree description of Coulomb-interacting electrons. This equation is solved by standard numerical tools and the results are interpreted in terms of approximated analytical formulas. For growing intensity, we observe a redshift of the effective resonance frequency due to the reduction of the electric dipole moment and the corresponding suppression of the depolarization shift. The competition between coherent nonlinearities and incoherent saturation effects is discussed. The strength of the resulting optical nonlinearity is estimated across different frequency ranges from mid-IR to THz with an eye to ongoing experiments on Bose-Einstein condensation of intersubband polaritons and to the speculative exploration of quantum optical phenomena such as single-photon emission in the mid-IR and THz windows

Viscoelastic response of contractile filament bundles

The actin cytoskeleton of adherent tissue cells often condenses into filament bundles contracted by myosin motors, so-called stress fibers, which play a crucial role in the mechanical interaction of cells with their environment. Stress fibers are usually attached to their environment at the endpoints, but possibly also along their whole length. We introduce a theoretical model for such contractile filament bundles which combines passive viscoelasticity with active contractility. The model equations are solved analytically for two different types of boundary conditions. A free boundary corresponds to stress fiber contraction dynamics after laser surgery and results in good agreement with experimental data. Imposing cyclic varying boundary forces allows us to calculate the complex modulus of a single stress fiber.Comment: Revtex with 24 pages, 7 Postscript figures included, accepted for publication in Phys. Rev.

Nonlinear frequency mixing in quantum cascade lasers: Towards broadband wavelength shifting and THz up-conversion

Terahertz (THz) sideband generation on a near-infrared (NIR) carrier has been recently demonstrated using quantum cascade lasers (QCL), with potential applications in wavelength shifting and THz up-conversion. However, the NIR wavelength range and nonlinear efficiency were severely limited by absorption. Here we overcome this drawback through a novel reflection geometry, whilst preserving a large interaction area. As well as insights into the nonlinear mechanism, this allows a much large range of NIR pump energies, relaxing the criteria of using particular excitation wavelengths

Monolithic echo-less photoconductive switches for high-resolution terahertz time-domain spectroscopy

Interdigitated photoconductive (IPC) switches are convenient sources and detectors for terahertz (THz) time domain spectroscopy. However, reflection of the emitted or detected radiation within the device substrate can lead to echoes that inherently limits the spectroscopic resolution achievable. In this work, we design and realize low-temperature-grown-GaAs (LT-GaAs) IPC switches for THz pulse generation and detection that suppresses such unwanted echoes. This is realized through a monolithic geometry of an IPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less IPC source, enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used

Far-field engineering of metal -metal terahertz quantum cascade lasers with integrated horn antennas

The far-field of metal-metal terahertz quantum cascade lasers is greatly improved through integrated and stable planar horn antennas on top of the QCL ridge. The antenna structures introduce a gradual change in the high modal confinement of metal-metal waveguides and permit an improved far-field, showing a five times increase in the emitted output power. The two dimensional far-field patterns are measured at 77K and compared to electromagnetic simulations. The influence of parasitic high order transverse modes are restricted through the engineering of antenna structure (ridge and antenna width) to couple out the fundamental mode only