External amplitude and frequency modulation of a terahertz quantum cascade laser using metamaterial/graphene devices.

Active control of the amplitude and frequency of terahertz sources is an essential prerequisite for exploiting a myriad of terahertz applications in imaging, spectroscopy, and communications. Here we present a optoelectronic, external modulation technique applied to a terahertz quantum cascade laser which holds the promise of addressing a number of important challenges in this research area. A hybrid metamaterial/graphene device is implemented into an external cavity set-up allowing for optoelectronic tuning of feedback into a quantum cascade laser. We demonstrate powerful, all-electronic, control over the amplitude and frequency of the laser output. Full laser switching is performed by electrostatic gating of the metamaterial/graphene device, demonstrating a modulation depth of 100%. External control of the emission spectrum is also achieved, highlighting the flexibility of this feedback method. By taking advantage of the frequency dispersive reflectivity of the metamaterial array, different modes of the QCL output are selectively suppressed using lithographic tuning and single mode operation of the multi-mode laser is enforced. Side mode suppression is electrically modulated from ~6 dB to ~21 dB, demonstrating active, optoelectronic modulation of the laser frequency content between multi-mode and single mode operation.

Hyperuniform disordered terahertz quantum cascade laser.

Laser cavities have been realized in various different photonic systems. One of the forefront research fields regards the investigation of the physics of amplifying random optical media. The random laser is a fascinating concept because, further to the fundamental research investigating light transport into complex media, it allows us to obtain non-conventional spectral distribution and angular beam emission patterns not achievable with conventional approaches. Even more intriguing is the possibility to engineer a priori the optical properties of a disordered distribution in an amplifying medium. We demonstrate here the realization of a terahertz quantum cascade laser in an isotropic hyperuniform disordered distribution exhibiting unique features, such as the presence of a photonic band gap, low threshold current density, unconventional angular emission and optical bistability.

Hollow metallic waveguides integrated with terahertz quantum cascade lasers.

We present the realization of a compact, monolithically integrated arrangement of terahertz quantum cascade lasers with hollow metallic cylindrical waveguides. By directly mounting a copper pipe to the end facet of a double metal waveguide, it was possible to significantly improve the far field emission from such a sub-wavelength plasmonic mode, while preserving the characteristic performance of the laser. Careful alignment of the quantum cascade laser and the hollow waveguide is required in order to prevent the excitation of higher order/mixed modes as predicted with a high degree of accuracy by a theoretical model. Finally, this approach proved to be a superior method of beam shaping when compared to other in situ arrangements, such as a silicon hyper-hemispherical lens glued to the facet, which are presented.

Cluster of cases of Salmonella enterica serotype Rissen infection in a general hospital, Italy, 2007.

In 2007, three strains of Salmonella enterica serotype Rissen (S. Rissen) were isolated in the laboratory of diagnostic microbiology of the General Hospital of Prato, Tuscany, Italy, over a 1 month and half interval of time. The first isolate was recovered on January 26 from an outpatient with enteritis. Then, two strains were isolated on February 16 and March 11 respectively, from central venous catheters of patients who were being hospitalized in two departments of the Hospital. An epidemiologically linked cluster of cases of salmonellosis was suspected. The three strains were submitted to single enzyme-amplified fragment length polymorphism (SE-AFLP) and XbaI macrorestriction and pulsed-field gel electrophoresis (PFGE) that yielded undistinguishable profiles. Epidemiological investigations failed to identify a common source of infection within the Hospital. Moreover, the third patient had been exclusively total parenteral nutrition fed since his admission with a stomach cancer diagnosis. The first patient had a community-acquired infection, but the source of her illness was uncertain. Twenty-five further isolates identified in the years 2004-2007 in the same geographical area showed distinctly different PFGE and SE-AFLP patterns. The three patients seemed to represent a cluster of epidemiologically unrelated cases caused by a previously never recognized S. Rissen strain. Rapid subtyping of isolates is essential in the early investigation of potential outbreaks, but synthesis of conventional and molecular epidemiological investigation and availability of surveillance data is often critical to prevent the initiation of time-consuming, expensive and ineffective further investigations and control interventions.

Differential near-field scanning optical microscopy with THz quantum cascade laser sources.

We have realized a differential Near-field Scanning Optical Microscope (NSOM) working with subwavelength resolution in the THz spectral region. The system employs a quantum cascade laser emitting at lambda approximately 105 microm as source, and the method, differently from conventional NSOM, involves diffracting apertures with size comparable to the wavelength. This concept ensures a higher signal-to-noise level at the expense of an additional computational step. In the implementation here reported lambda/10 resolution has been achieved; present limiting factors are investigated through finite difference time domain simulations.

UV second harmonic generation at 266 nm in He+ implanted beta-BaB2O4 optical waveguides.

We report on the second harmonic generation of deep UV light in beta -BaB(2)O(4) (BBO) waveguides pumped by a frequency-doubled continuous-wave Nd:YAG laser. An output power of 0.32 mW at 266 nm has been achieved for an internal pump power of 670 mW. Optical channel waveguides in BBO crystals were produced by He(+) ion implantation, lithographic masking and ion etching. The linear and nonlinear optical properties and the power handling capability of these waveguides are presented.

Outbreak of Clostridium difficile diarrhoea in an orthopaedic unit: evidence by phage-typing for cross-infection.

In a three-week period five patients had diarrhoea in an orthopaedic unit. The first case was clinically diagnosed as pseudomembranous colitis but the causative agent was not sought. Of the remaining cases, two were Clostridium difficile positive. The outbreak then apparently ceased, but during the following several days two of seven stool samples taken at random from asymptomatic patients yielded C. difficile. Phage-typing of the isolates showed that all apparently belonged to the same strain.

[Pyocin typing of 111 strains of Pseudomonas aeruginosa isolated in Tuscany, using the Gillies and Govan method]. / Tipizzazione piocinica secondo Gillies e Govan di 111 stipiti di "Pseudomonas aeruginosa" isolati in Toscana.

Pseudomonas aeruginosa strains from Tuscany have been typed for pyocine production against Govan and Gillies' extended set of indicator strains; results have been expressed following a binary code. Among 111 strains only 6 could not be typed; the remaining 105 strains (94.6%) presented 59 different patterns, 44 of which were represented by one isolate only. The most commonly encountered pattern (n. 8045, corresponding to Govan and Gillies' subtype 1e) was shared by 13 strains. Isolates from outpatients or from the environment tended to a uniform distribution of pyocine patterns; those from two different hospitals tended to group into distinct subtypes.