A. Giles Davies

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Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz)(More)
Terahertz (THz) quantum cascade lasers (QCLs) are currently the most advanced electrically pumped semiconductor lasers in the spectral range 1–5 THz. However, their operation at room temperature is still an unresolved challenge. In this paper, we discuss our efforts to improve the temperature performance of these devices. In particular, we present THz QCLs(More)
We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding(More)
BACKGROUND The dissection of biological pathways and of the molecular basis of disease requires devices to analyze simultaneously a staggering number of protein isoforms in a given cell under given conditions. Such devices face significant challenges, including the identification of probe molecules specific for each protein isoform, protein immobilization(More)
We report the use ofterahertz time-domain spectroscopy for thestudy of two therapeutic bio-molecules:glucose and uric acid. Terahertztransmission spectra of crystalline samplesof both molecules were measured between 0.1-3.0 THz using an evacuated spectroscopysystem. We propose that the stereo-isomersof glucose show spectral featuresoriginating from(More)
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(More)
We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We(More)
We investigate the effect of substrate thickness on the transmission bandwidth of on-chip terahertz-frequency-range planar Goubau lines both experimentally and theoretically. The bandwidth and frequency resolution are improved through substrate thinning and geometry modifications (reducing reflections arising from the THz photoconductive generators and(More)
Semiconductor lasers based on two-dimensional photonic crystals generally rely on an optically pumped central area, surrounded by un-pumped, and therefore absorbing, regions. This ideal configuration is lost when photonic-crystal lasers are electrically pumped, which is practically more attractive as an external laser source is not required. In this case,(More)
Fourier-transform infrared transmission spectroscopy has been used for the determination of glucose concentration in whole blood samples from 28 patients. A 4-vector partial least-squares calibration model, using the spectral range 950-1200 cm(-1), yielded a standard-error-of-prediction of 0.59 mM for an independent test set. For blood samples from a single(More)