Terahertz frequency quantum cascade lasers for use as waveguide-integrated local oscillators

Since their first demonstration in 2002, the performance of terahertz frequency quantum cascade lasers has developed extremely rapidly. We consider the potential use of terahertz frequency quantum cascade lasers as local oscillators in satellite-borne instrumentation for future Earth observation and planetary science missions. A specific focus will be on the development of compact, waveguide-integrated, heterodyne detection systems for the supra-terahertz range

Waveguide-integrated Terahertz Quantum Cascade Lasers for use as Local Oscillators

Terahertz-frequency quantum cascade lasers (THz QCLs) are compact sources of 1–5 THz radiation, which show great promise for use as local oscillators in satellite-borne heterodyne radiometers. We present a waveguide-integration scheme, in which a THz QCL is mounted in a copper heat-sink block, with radiation outcoupled into a precision micromachined rectangular waveguide. Electrical bias is provided by an integrated SMA connector and mounting points are provided for attachment to a cryocooler and a temperature sensor. The integration scheme is mechanically robust and is shown to have negligible impact on the thermal performance or threshold current of the device. The emitted beam quality is significantly improved, compared with that of a conventional device, with single-lobed profile with divergence <20 degrees

Detection of 2.2-3.5 Terahertz Radiation Using a Quasi-Optically Mounted Planar Schottky Diode

Practical supra-terahertz (1–5 THz) heterodyne radiometry systems require compact local oscillator and mixer components, which are suitable for robust waveguide integration. We demonstrate detection of radiation emitted by quantum cascade lasers at frequencies between 2.2 and 3.5 THz using room-temperature quasi-optically mounted planar Schottky diodes. These diodes are more readily integrated into waveguides than point-contact diodes, do not require the cryogenic environment of hot-electron bolometers and offer potentially better noise performance than superlattice devices

Feedhorn-integrated THz QCL local oscillators for the LOCUS atmospheric sounder

The LOCUS atmospheric sounder is a satellite-borne THz radiometer concept, for studying molecular species in the mesosphere and lower thermosphere. We report waveguide-integrated THz quantum-cascade lasers for use as 3.5 THz local oscillators. A waveguide-integration scheme, using an integrated diagonal feedhorn significantly improves power outcoupling. 1.3 mW THz emission is demonstrated in a space-qualified Stirling cryocooler at 57 K, with ∼15° beam divergence

Bio-psychosocial determinants of cardiovascular disease in a rural population on Crete, Greece: formulating a hypothesis and designing the SPILI-III study

Background: In 1988, the SPILI project was established in order to evaluate the cardiovascular disease (CVD) risk profile of the inhabitants of Spili, in rural Crete, Greece. The first reports from this project revealed that against the unfavourable risk factors’ profile observed, only a few men with a previous myocardial infarction were encountered. A follow-up study (SPILI II) was performed twelve years after the initial examination, and the unfavourable cardiovascular risk profile was re-confirmed. Presentation of the Hypothesis: This paper presents a hypothesis formulated on the basis of previous research to investigate if dynamic psycho-social determinants, including social coherence of the local community, religiosity and spirituality, are protective against the development of coronary heart disease in a well-defined population. Testing the Hypothesis: A follow-up examination of this Cretan cohort is currently being performed to assess the link between psychosocial factors and CVD. Psychosocial factors including sense of control, religiosity and spirituality are assessed in together with conventional CVD risk factors. Smoking and alcohol consumption, as well as dietary habits and activity levels are recorded. Oxidative stress and inflammatory markers, as well as ultrasound measurement of carotid intima media thickness, a preclinical marker of atherosclerosis, will also be measured. Implications of the hypothesis tested: The issue of the cardio-protective effect of psycho-social factors would be revisited based on the results of this Cretan cohort; nevertheless, further research is needed across different subpopulations in order to establish a definite relationship. A comprehensive approach based on the aspects of biosocial life may result in more accurate CVD risk management

Waveguide-integrated terahertz-frequency quantum cascade lasers for detection of trace-gas species

We demonstrate high-performance THz QCLs lasing at 2.2, 2.53, 3.5 and 4.7 THz, which target absorption lines of water, methane, hydroxyl and atomic oxygen respectively. Reliable single-mode targeting of gas species is obtained through the use of a photonic lattice design. A highly reproducible micro-machined waveguide block yields narrow beam-divergence and enables future integration of a complete THz heterodyne system including local-oscillator, mixer, and feed-horn

The association between family and community social capital and health risk behaviours in young people: an integrative review

Background: Health risk behaviours known to result in poorer outcomes in adulthood are generally established in late childhood and adolescence. These ‘risky’ behaviours include smoking, alcohol and illicit drug use and sexual risk taking. While the role of social capital in the establishment of health risk behaviours in young people has been explored, to date, no attempt has been made to consolidate the evidence in the form of a review. Thus, this integrative review was undertaken to identify and synthesise research findings on the role and impact of family and community social capital on health risk behaviours in young people and provide a consolidated evidence base to inform multi-sectorial policy and practice.&lt;p&gt;&lt;/p&gt; Methods: Key electronic databases were searched (i.e. ASSIA, CINAHL, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Database of Abstracts of Reviews of Effects, Embase, Medline, PsycINFO, Sociological Abstracts) for relevant studies and this was complemented by hand searching. Inclusion/exclusion criteria were applied and data was extracted from the included studies. Heterogeneity in study design and the outcomes assessed precluded meta-analysis/meta-synthesis; the results are therefore presented in narrative form.&lt;p&gt;&lt;/p&gt; Results: Thirty-four papers satisfied the review inclusion criteria; most were cross-sectional surveys. The majority of the studies were conducted in North America (n=25), with three being conducted in the UK. Sample sizes ranged from 61 to 98,340. The synthesised evidence demonstrates that social capital is an important construct for understanding the establishment of health risk behaviours in young people. The different elements of family and community social capital varied in terms of their saliency within each behavioural domain, with positive parent–child relations, parental monitoring, religiosity and school quality being particularly important in reducing risk.&lt;p&gt;&lt;/p&gt; Conclusions: This review is the first to systematically synthesise research findings about the association between social capital and health risk behaviours in young people. While providing evidence that may inform the development of interventions framed around social capital, the review also highlights key areas where further research is required to provide a fuller account of the nature and role of social capital in influencing the uptake of health risk behaviours.&lt;p&gt;&lt;/p&gt

Problematic online behaviors among adolescents and emerging adults: associations between cyberbullying perpetration, problematic social media use, and psychosocial factors

Over the past two decades, young people's engagement in online activities has grown markedly. The aim of the present study was to examine the relationship between two specific online behaviors (i.e., cyberbullying perpetration, problematic social media use) and their relationships with social connectedness, belongingness, depression, and self-esteem among high school and university students. Data were collected from two different study groups via two questionnaires that included the Cyberbullying Offending Scale, Social Media Use Questionnaire, Social Connectedness Scale, General Belongingness Scale, Short Depression-Happiness Scale, and Single Item Self-Esteem Scale. Study 1 comprised 804 high school students (48% female; mean age 16.20 years). Study 2 comprised 760 university students (60% female; mean age 21.48 years). Results indicated that problematic social media use and cyberbullying perpetration (which was stronger among high school students) were directly associated with each other. Belongingness (directly) and social connectedness (indirectly) were both associated with cyberbullying perpetration and problematic social media use. Path analysis demonstrated that while age was a significant direct predictor of problematic social media use and cyberbullying perpetration among university students, it was not significant among high school students. In both samples, depression was a direct predictor of problematic social media use and an indirect predictor of cyberbullying perpetration. However, majority of these associations were relatively weak. The present study significantly adds to the emerging body of literature concerning the associations between problematic social media use and cyberbullying perpetration

Analysis of deuteration reactions using self-mixing in a terahertz quantum-cascade laser

We present a THz-QCL spectroscopy technique, for analyzing deuteration reactions in gases. This is an important analytical chemistry technique, underpinning mechanistic studies. We use a self-mixing interferometry approach, in which radiation from a multimode QCL is fed-back into the device, via a gas cell, causing perturbations to the QCL voltage. This enables “detector-free” sensing over a 17-GHz range, allowing speciated measurements of reactions involving H2O, D2O, HDO, CH3OH and CH2DOD

Electromagnetic modelling of a terahertz-frequency quantum-cascade laser integrated with dual diagonal feedhorns

We present an electromagnetic model of a THz QCL, integrated with a micro-machined waveguide and dual diagonal feedhorns, enabling simultaneous access to both facets of the QCL. A hybrid finite-element/Fourier transform approach enables analysis of both the near and far-fields in agreement with experimental observations. The far-field pattern shows enhancement of the beam profile when compared with an unmounted QCL, in terms of beam divergence and side-lobe suppression ratio