Saturday, February 6, 2016

Abstract-Efficient Terahertz detection in black-phosphorus nano-transistors with selective and controllable plasma-wave, bolometric and thermoelectric response

Leonardo Viti, Jin Hu, Dominique Coquillat, Antonio Politano, Wojciech Knap,  Miriam S. Vitiello,


The ability to convert light into an electrical signal with high efficiencies and controllable dynamics, is a major need in photonics and optoelectronics. In the Terahertz (THz) frequency range, with its exceptional application possibilities in high data rate wireless communications, security, night-vision, biomedical or video-imaging and gas sensing, detection technologies providing efficiency and sensitivity performances that can be “engineered” from scratch, remain elusive. Here, by exploiting the inherent electrical and thermal in-plane anisotropy of a flexible thin flake of black-phosphorus (BP), we devise plasma-wave, thermoelectric and bolometric nano-detectors with a selective, switchable and controllable operating mechanism. All devices operates at room-temperature and are integrated on-chip with planar nanoantennas, which provide remarkable efficiencies through light-harvesting in the strongly sub-wavelength device channel. The achieved selective detection (5–8 V/W responsivity) and sensitivity performances (signal-to-noise ratio of 500), are here exploited to demonstrate the first concrete application of a phosphorus-based active THz device, for pharmaceutical and quality control imaging of macroscopic samples, in real-time and in a realistic setting.

Friday, February 5, 2016

OT- LUNA Blog-Validating composite spring designs with high definition fiber optic sensing (HD-FOS)


July 2015 Vehicle Dynamics International Magazine – presents a case study using composites in automotive suspension design

In the July 2015 issue of Vehicle Dynamics International magazine, the author of the article ‘Lightest Touch’ asks if using composites within an automotive chassis is the key to achieving EU and US mileage targets. The article presents a case study of a light weighting program for the 2013 Peugeot 208 Hybrid FE, targeting a 20% reduction in vehicle weight.  Peugeot achieved this goal in large part by focusing on substituting glass fiber resin composite materials for the steel used in the vehicle’s suspension systems.  The suspension/chassis components represent a substantial percentage of vehicle weight exceeded only by the powertrain and body. Furthermore, the fabrication of suspension components from composite materials more easily align with the current state of composite manufacturing processes. Within the automotive industry, suspension systems and other chassis components may represent the low hanging fruit for the early adopters of composites.
Transitioning from traditional metals to composites – challenges and unknowns
Composite materials have gained significant traction in both the military and commercial aerospace sectors, owing to their ability to offer a high strength-to-weight ratio.  The introduction of composites in aerospace has not been problem-free however, and in many respects the aerospace industry remains on a learning curve.  Designers in the automotive industry need to be aware that the anisotropic and heterogeneous characteristics of composites limit the availability of published material property data. Without this data, engineers can no longer be certain that computer aided engineering (CAE) and other simulation tools will provide accurate predictions of component performance.  Composite materials offer additional challenges in manufacturing and engineers need to ensure that part-to-part variability is well understood and under control. Within the aerospace industry the challenges posed by the use of composites is addressed, in part, by adopting new technologies in the test and validation methods used for composite structures. High definition fiber optic sensing (HD-FOS) from Luna is a key test and validation technology used at all levels of the aerospace value chain.
Instrumenting a composite part with HD-FOS – achieving a full field view of strain impossible with strain gages
Strain gages are the traditional method of measuring strain on springs. This method of point sensing is very limiting as there are only so many strain gages that can be mounted to a spring. Each strain gage needs to be individually wired and provides just a single strain measurement for every location instrumented. By contrast a single HD-FOS sensor can be mounted along the entire length of a spring and provides strain measurements in increments of one millimeter.  This method of measuring strain of springs offers simplicity of instrumentation as well as a full characterization of the strain profile simply unobtainable with any other method. Figure 1 shows a steel helical spring instrumented with an HD-FOS sensor. The sensor bonding method is similar to that used by strain gages. Figure 2 shows the data taken from a single HD-FOS sensor mounted on the helical spring when in compression. The color-mapped image shows a 2D visualization of the strain profile; the strain vs length plot shows the high definition strain measurements along the length of the spring. The advantage offered by HD-FOS as compared to one, two, or even a dozen individual strain gages is very clear and this advantage compounds as component designs move away from metals and toward new advanced composite materials. 
Figure 1 – Steel Engine Spring Instrumented with HD-FOS Sensor
Figure 1 – Steel Engine Spring Instrumented with HD-FOS Sensor
Figure 2 – HD-FOS Strain Data – Steel Valve Spring

In summary – HD-FOS in automotive, benefiting from the experience of aerospace
The adoption of composite materials in the automotive industry is a matter of when, not if, and the makers of suspension systems are likely to be early adopters of composite materials. The automotive industry can learn from the experience of aerospace including the use of HD-FOS sensing when testing components and structures made from composite materials.  In the aerospace industry, HD-FOS is used at all levels of the value chain; from characterizing the behavior of new materials to the structural testing of large assemblies. HD-FOS is well suited to uncover the strain gradients and other incongruencies associated with composite materials as well as the new machining, fastening, and joining methods that accompany their use.         
To learn more about how Luna’s ODiSI with HD-FOS fits with your applications, click here.
To talk to someone call 540.961.5190 or to ask a question or request a quote click here solutions@lunainc.com 
  1. Reference: John O’Brien, Vehicle Dynamics International – July 2015, Lightest Touch
  2. Reference: Luna Innovations test data for Mubea helical valve spring

Abstract-Backward spoof surface wave in plasmonic metamaterial of ultrathin metallic structure


Backward wave with anti-parallel phase and group velocities is one of the basic properties associated with negative refraction and sub-diffraction image that have attracted considerable interest in the context of photonic metamaterials. It has been predicted theoretically that some plasmonic structures can also support backward wave propagation of surface plasmon polaritons (SPPs), however direct experimental demonstration has not been reported, to the best of our knowledge. In this paper, a specially designed plasmonic metamaterial of corrugated metallic strip has been proposed that can support backward spoof SPP wave propagation. The dispersion analysis, the full electromagnetic field simulation and the transmission measurement of the plasmonic metamaterial waveguide have clearly validated the backward wave propagation with dispersion relation possessing negative slope and opposite directions of group and phase velocities. As a further verification and application, a contra-directional coupler is designed and tested that can route the microwave signal to opposite terminals at different operating frequencies, indicating new application opportunities of plasmonic metamaterial in integrated functional devices and circuits for microwave and terahertz radiation.

Abstract-Surface and interface states of Bi2Se3 thin films investigated by optical second-harmonic generation and terahertz emission

We investigate the surface and interface states of BiSe thin films by using the second-harmonic generation technique. Distinct from the surface of bulk crystals, the film surface and interface show the isotropic azimuth dependence of second-harmonic intensity, which is attributed to the formation of randomly oriented domains on the in-plane. Based on the nonlinear susceptibility deduced from the model fitting, we determine that the surface band bending induced in a space charge region occurs more strongly at the film interface facing the AlO substrate or capping layer compared with the interface facing the air. We demonstrate that distinct behavior of the terahertz electric field emitted from the samples can provide further information about the surface electronic state of BiSe.

Abstract-Dynamics of ultra-broadband terahertz quantum cascade lasers for comb operation.


We present an experimental investigation of the multimode dynamics and the coherence of terahertz quantum cascade lasers emitting over a spectral bandwidth of ~1THz. The devices are studied in free-running and under direct RF modulation. Depending on the pump current we observe different regimes of operation, where RF spectra displaying single and multiple narrow beat-note signals alternate with spectra showing a single beat-note characterized by an intense phase-noise, extending over a bandwidth up to a few GHz. We investigate the relation between this phase-noise and the dynamics of the THz modes through the electro-optic sampling of the laser emission. We find that when the phase-noise is large, the laser operates in an unstable regime where the lasing modes are incoherent. Under RF modulation of the laser current such instability can be suppressed and the modes coherence recovered, while, simultaneously, generating a strong broadening of the THz emission spectrum.