Long-term stability of GaAs/AlAs terahertz quantum-cascade lasers

We have investigated high-performance GaAs/AlAs terahertz (THz) quantum-cascade lasers (QCLs) with respect to the long-term stability of their operating parameters. The output power of lasers that contain an additional, thick AlAs refractive-index contrast layer underneath the cascade structure decreases after three months by about 35%. The deterioration of these lasers is attributed to the oxidation processes in this contrast layer starting from the facets. However, GaAs/AlAs THz QCLs with an Al0.9Ga0.1As refractive-index contrast layer exhibit long-term stability of the operating parameters over many years even when they are exposed to atmospheric conditions. Therefore, these lasers are promising high-power radiation sources in the terahertz spectral region for commercial applications

Urban habitat restoration provides a human health benefit through microbiome rewilding: the Microbiome Rewilding Hypothesis

Restoration aims to return ecosystem services, including the human health benefits of exposure to green space. The loss of such exposure with urbanization and industrialization has arguably contributed to an increase in human immune dysregulation. The Biodiversity and Old Friends hypotheses have described the possible mechanisms of this relationship, and suggest that reduced exposure to diverse, beneficial microorganisms can result in negative health consequences. However, it is unclear whether restoration of biodiverse habitat can reverse this effect, and what role the environmental microbiome might have in such recovery. Here, we propose the Microbiome Rewilding Hypothesis, which specifically outlines that restoring biodiverse habitats in urban green spaces can rewild the environmental microbiome to a state that enhances primary prevention of human disease. We support our hypothesis with examples from allied fields, including a case study of active restoration that reversed the degradation of the soil bacterial microbiome of a former pasture. This case study used high-throughput amplicon sequencing of environmental DNA to assess the quality of a restoration intervention in restoring the soil bacterial microbiome. The method is rapid, scalable, and standardizable, and has great potential as a monitoring tool to assess functional outcomes of green-space restoration. Evidence for the Microbiome Rewilding Hypothesis will help motivate health professionals, urban planners, and restoration practitioners to collaborate and achieve co-benefits. Co-benefits include improved human health outcomes and investment opportunities for biodiversity conservation and restoration.Jacob G. Mills, Philip Weinstein, Nicholas J.C. Gellie, Laura S. Weyrich, Andrew J. Lowe, Martin F. Bree

Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser

We demonstrate phase-locking of a 2.7-THz metalmetal waveguide quantum cascade laser (QCL) to an external microwave signal. The reference is the 15th harmonic, generated by a semiconductor superlattice nonlinear device, of a signal at 182 GHz, which itself is generated by a multiplier-chain (x2x3x2) from a microwave synthesizer at 15 GHz. Both laser and reference radiations are coupled into a hot electron bolometer mixer, resulting in a beat signal, which is fed into a phase-lock loop. Spectral analysis of the beat signal (see fig. 1) confirms that the QCL is phase locked. This result opens the possibility to extend heterodyne interferometers into the far-infrared range

Tunable and compact dispersion compensation of broadband THz quantum cascade laser frequency combs

Miniaturized frequency combs (FCs) can be self-generated at terahertz (THz) frequencies through four-wave mixing in the cavity of a quantum cascade laser (QCL). To date, however, stable comb operation is only observed over a small operational current range in which the bias-depended chromatic dispersion is compensated. As most dispersion compensation techniques in the THz range are not tunable, this limits the spectral coverage of the comb and the emitted output power, restricting potential applications in, for example, metrology and ultrashort THz pulse generation. Here, we demonstrate an alternative architecture that provides a tunable, lithographically independent, control of the free-running coherence properties of THz QCL FCs. This is achieved by integrating an on-chip tightly coupled mirror with the QCL cavity, providing an external cavity and hence a tunable Gires Tournois interferometer (GTI). By finely adjusting the gap between the GTI and the back-facet of an ultra-broadband, high dynamic range QCL, we attain wide dispersion compensation regions, where stable and narrow (~3 kHz linewidth) single beatnotes extend over an operation range that is significantly larger than that of dispersion-dominated bare laser cavity counterparts. Significant reduction of the phase noise is registered over the whole QCL spectral bandwidth (1.35 THz). This agile accommodation of a tunable dispersion compensator will help enable uptake of QCL-combs for metrological, spectroscopic and quantum technology−oriented applications

Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser

We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 μm with a power noise spectral density below −50 dB/Hz, for a sampling time of 10 ms/pixel

Networked and embedded scientific experiments will improve restoration outcomes

Vast areas of degraded land have proliferated worldwide. In response to this transformation, ambitious targets have been set to restore degraded ecosystems, such as the the Bonn Challenge, which aims to restore 350 million ha of forestland by 2030. Achieving such goals will require a larger evidence base of restoration studies, which could be realized by systematically embedding scientific experiments within restoration programs. We examine the feasibility of this strategy with examples of successful transdisciplinary research involving embedded experiments in associated fields, and recommend that such field sites be linked to create a global network of embedded experiments. To unify a networked approach, we call on restoration stakeholders to develop acceptable industry standards of experimental design. Finally, we suggest how to use this strategy effectively to meet the biome-scale challenges of the coming decades.Nicholas JC Gellie, Martin F Breed, Peter E Mortimer, Rhett D Harrison, Jianchu Xu and Andrew J Low

"Status of Students' Perceptions and Self-efficacy on the Use of ICT"

Abstract. This study investigated the status of students' perceptions and self-efficacy on the use of information and communications technology. The respondents are fifty 4 th Year Bachelor of Elementary Education major in English students of the Department of Professional Education, College of Education, Mindanao State University -Iligan Institute of Technology, Iligan City, Philippines. The study employed the descriptive-correlation method. An adapted questionnaire composed of three parts was used to gather needed data. Results of the survey revealed the following: most of the respondents are 19 years old; more than one-half have their own computer units but only 18 of them have Internet connection at home; 68% of the respondents daily use of computer is 1 -3 hours; in terms of perceptions with regard to interest, majority wants to learn more about ICT however they are not very interested on using ICT in making course reflections, sharing work or outputs or working collaboratively with classmates; word processors, web browsers, search engines and emails are the most commonly used ICT tools while desktop publishing, video editing software and social bookmarking are the least used; in general, the respondents frequently use ICT tools; respondents foremost purpose of using ICT is for educational research; generally, respondents possess a "good" skill on the use of ICT tools; there is a negative relationship between the frequency of ICT use and age -as age increases, the frequency of ICT use decreases; there is a strong / significant positive relationship between perception towards ICT and self-efficacy on the use of ICT. Results of the study implies that strengthening of ICT trainings in the in-service level is needed so that teachers can update themselves and cater to the needs of the 21 st century learners

Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis

The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser