Coherence measurements of polaritons in thermal equilibrium reveal a power law for two-dimensional condensates.

We have created a spatially homogeneous polariton condensate in thermal equilibrium, up to very high condensate fraction. Under these conditions, we have measured the coherence as a function of momentum and determined the total coherent fraction of this boson system from very low density up to density well above the condensation transition. These measurements reveal a consistent power law for the coherent fraction as a function of the total density over nearly three orders of its magnitude. The same power law is seen in numerical simulations solving the two-dimensional Gross-Pitaevskii equation for the equilibrium coherence.

Visualization of localized facet Joule heating induced optical degradation on mid-infrared quantum cascade lasers.

Reversible lasing performance degradation is investigated on an uncoated actively- biased GaAs/Al0.45Ga0.55As mid-infrared quantum cascade laser (MIR-QCL) facet. The surface temperature rises (ΔT) on the MIR QCL are characterized before and after the device undergoes an accelerated aging burn-in test, followed by hydrogen plasma treatment. The data is visualized by spatially resolved time-domain thermoreflectance (SR-TDTR) microscopy. On the laser facet, ΔT decreases with a drop in lasing performance and ΔT increases with an increase in lasing performance. Along the laser cavity, the thermal property change is negligible before and after the aging test, independent of the optical performance change. The results verify that thermal-induced facet oxidation is the main reason for the rapid degradation of the lasing performance in the early aging stage.

Semiconductor nanowire metamaterial for broadband near-unity absorption.

The realization of a semiconductor near-unity absorber in the infrared will provide new capabilities to transform applications in sensing, health, imaging, and quantum information science, especially where portability is required. Typically, commercially available portable single-photon detectors in the infrared are made from bulk semiconductors and have efficiencies well below unity. Here, we design a novel semiconductor nanowire metamaterial, and show that by carefully arranging an InGaAs nanowire array and by controlling their shape, we demonstrate near-unity absorption efficiency at room temperature. We experimentally show an average measured efficiency of 93% (simulated average efficiency of 97%) over an unprecedented wavelength range from 900 to 1500 nm. We further show that the near-unity absorption results from the collective response of the nanowire metamaterial, originating from both coupling into leaky resonant waveguide and transverse modes. These coupling mechanisms cause light to be absorbed directly from the top and indirectly as light scatters from one nanowire to neighbouring ones. This work leads to the possible development of a new generation of quantum detectors with unprecedented broadband near-unity absorption in the infrared, while operating near room temperature for a wider range of applications.

Six-level hybrid extraction/injection scheme terahertz quantum cascade laser with suppressed thermally activated carrier leakage.

This work presents a six-level scheme terahertz (THz) quantum cascade laser (QCL) design in which the resonant-phonon (RP) and the scattering-assisted (SA) injection/extraction are combined within a single Al0.15Ga0.85As/GaAs based structure. By utilizing extra excited states for hybrid extraction/injection channels, this design minimizes the appearance of an intermediate negative differential resistance (NDR) before the lasing threshold. The final negative differential resistance is observed up to 260K and a high characteristic temperature of 259 K is measured. These observations imply very effective suppression of pre-threshold electrical instability and thermally activated leakage current. In addition, the impact of critical design parameters of this scheme is investigated.

Planar integrated metasurfaces for highly-collimated terahertz quantum cascade lasers.

We report planar integration of tapered terahertz (THz) frequency quantum cascade lasers (QCLs) with metasurface waveguides that are designed to be spoof surface plasmon (SSP) out-couplers by introducing periodically arranged SSP scatterers. The resulting surface-emitting THz beam profile is highly collimated with a divergence as narrow as ~4° × 10°, which indicates a good waveguiding property of the metasurface waveguide. In addition, the low background THz power implies a high coupling efficiency for the THz radiation from the laser cavity to the metasurface structure. Furthermore, since all the structures are in-plane, this scheme provides a promising platform where well-established surface plasmon/metasurface techniques can be employed to engineer the emitted beam of THz QCLs controllably and flexibly. More importantly, an integrated active THz photonic circuit for sensing and communication applications could be constructed by incorporating other optoelectronic devices such as Schottky diode THz mixers, and graphene modulators and photodetectors.

Electronic temperatures of terahertz quantum cascade active regions with phonon scattering assisted injection and extraction scheme.

We measured the lattice and subband electronic temperatures of terahertz quantum cascade devices based on the optical phonon-scattering assisted active region scheme. While the electronic temperature of the injector state (j = 4) significantly increases by ΔT = T(e)(4) - T(L) ~40 K, in analogy with the reported values in resonant phonon scheme (ΔT ~70-110 K), both the laser levels (j = 2,3) remain much colder with respect to the latter (by a factor of 3-5) and share the same electronic temperature of the ground level (j = 1). The electronic population ratio n(2)/n(1) shows that the optical phonon scattering efficiently depopulates the lower laser level (j = 2) up to an electronic temperature T(e) ~180 K.

An investigation on optimum ridge width and exposed side strips width of terahertz quantum cascade lasers with metal-metal waveguides.

The impacts of side exposed side strips (for high order modes suppression) and ridge width on terahertz (THz) quantum cascade laser (QCL) performance are investigated through numerical modeling and verified experimentally. Our results show that shrinking ridge width of THz QCLs with metal-metal waveguides leads to a substantial degradation of device performance due to higher optical loss resulting from the side-exposed strips in the highly-doped top contact layer. Nevertheless, the side-exposed strips facilitate single mode operation by strongly suppressing higher-order modes. An optimal width of the side exposed strips is obtained for achieving adequate higher-order mode suppression and maintaining sufficiently low fundamental mode loss.

Near-room-temperature mid-infrared quantum well photodetector.

We demonstrate InGaAs mid-infrared quantum well infrared photodetectors (MIR PV-QWIPs) that enable cost-effective mature GaAs-based detection and imaging technologies, with exceptional material uniformity, reproducibility, and yield, over a large area, with high spectral selectivity, innate polarization sensitivity, radiation hardness, high detectivity, and high speed operation at TEC temperatures without bias.

[Ectopic cervical pregnancy terminating in the birth of a live 1800 g infant]. / Ciaza ektopqwa szyjkowa zakonczona urodzeniem zywego 1800 g dziecka.

We present here a case of ectopic cervical pregnancy terminated in the birth of a live 1800 g infant, whose further development takes normal course. Wrong evaluation of the place of the developing pregnancy resulted in its growth up to 34th week. Finally, the placement of pregnancy was established after delivering the woman with a caesarean section, on the basis of macro and microscopic evaluation of the removed uterus. Extraordinary series of circumstances enabled such a long development of ectopic cervical pregnancy, on a scale unprecedented in literature. Ways of dealing with cervical pregnancy, which seriously endangers health and life of the patient, were also recalled.