Frequency stabilization of a terahertz quantum-cascade laser to the Lamb dip of a molecular absorption line.

We demonstrate the frequency stabilization of a terahertz quantum-cascade laser (QCL) to the Lamb dip of the absorption line of a DO rotational transition at 3.3809309 THz. To assess the quality of the frequency stabilization, a Schottky diode harmonic mixer is used to generate a downconverted QCL signal by mixing the laser emission with a multiplied microwave reference signal.

Laser emission at 4.5 THz from NH and a mid-infrared quantum-cascade laser as a pump source.

We present an optically pumped terahertz gas laser, which is based on a mid-infrared quantum-cascade laser as a pump source, a transversely pumped standing wave resonator, and NH as a gain medium. We observe several laser lines around 4.5 THz, corresponding to rotational transitions in the ν band of ammonia.

Role of active patient involvement in undergraduate medical education: a systematic review.

Objectives: To identify the scope of active patient involvement in medical education, addressing the current knowledge gaps relating to rationale and motivation for involvement, recruitment and preparation, roles, learning outcomes and key procedural contributors.

Methods: The authors performed a systematic search of the PubMed database of publications between 2003 and 2018. Original studies in which patients take on active roles in the development, delivery or evaluation of undergraduate medical education and written in English were eligible for inclusion.

Frequency and power stabilization of a terahertz quantum-cascade laser using near-infrared optical excitation.

We demonstrate a technique to simultaneously stabilize the frequency and output power of a terahertz quantum-cascade laser (QCL). This technique exploits frequency and power variations upon near-infrared illumination of the QCL with a diode laser. It does not require an external terahertz optical modulator.

Wideband, high-resolution terahertz spectroscopy by light-induced frequency tuning of quantum-cascade lasers.

Near-infrared optical excitation enables wideband frequency tuning of terahertz quantum-cascade lasers. In this work, we demonstrate the feasibility of the approach for molecular laser absorption spectroscopy. We present a physical model which explains the observed frequency tuning characteristics by the optical excitation of an electron-hole plasma.

Doppler-free spectroscopy with a terahertz quantum-cascade laser.

We report on the Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum-cascade laser and an absorption cell in a collinear pump-probe configuration. A Lamb dip with a sub-Doppler linewidth of 170 kHz is observed for a rotational transition of HDO.

Real-time gas sensing based on optical feedback in a terahertz quantum-cascade laser.

We report on real-time gas sensing with a terahertz quantum-cascade laser (QCL). The method is solely based on the modulation of the external cavity length, exploiting the intermediate optical feedback regime. While the QCL is operated in continuous-wave mode, optical feedback results in a change of the QCL frequency as well as its terminal voltage.

High-spectral-resolution terahertz imaging with a quantum-cascade laser.

We report on a high-spectral-resolution terahertz imaging system operating with a multi-mode quantum-cascade laser (QCL), a fast scanning mirror, and a sensitive Ge:Ga detector. By tuning the frequency of the QCL, several spectra can be recorded in 1.5 s during the scan through a gas cell filled with methanol (CHOH).

Evidence for frequency comb emission from a Fabry-Pérot terahertz quantum-cascade laser.

We report on a broad-band terahertz quantum-cascade laser (QCL) with a long Fabry-Pérot ridge cavity, for which the tuning range of the individual laser modes exceeds the mode spacing. While a spectral range of approximately 60 GHz (2 cm(-1)) is continuously covered by current and temperature tuning, the total emission range spans more than 270 GHz (9 cm(-1)). Within certain operating ranges, we found evidence for stable frequency comb operation of the QCL.

High-temperature, continuous-wave operation of terahertz quantum-cascade lasers with metal-metal waveguides and third-order distributed feedback.

Currently, different competing waveguide and resonator concepts exist for terahertz quantum-cascade lasers (THz QCLs). We examine the continuous-wave (cw) performance of THz QCLs with single-plasmon (SP) and metal-metal (MM) waveguides fabricated from the same wafer. While SP QCLs are superior in terms of output power, the maximum operating temperature for MM QCLs is typically much higher.

Frequency modulation spectroscopy with a THz quantum-cascade laser.

We report on a terahertz spectrometer for high-resolution molecular spectroscopy based on a quantum-cascade laser. High-frequency modulation (up to 50 MHz) of the laser driving current produces a simultaneous modulation of the frequency and amplitude of the laser output. The modulation generates sidebands, which are symmetrically positioned with respect to the laser carrier frequency.

Lateral distributed-feedback gratings for single-mode, high-power terahertz quantum-cascade lasers.

We report on terahertz quantum-cascade lasers (THz QCLs) based on first-order lateral distributed-feedback (lDFB) gratings, which exhibit continuous-wave operation, high output powers (>8 mW), and single-mode emission at 3.3-3.4 THz.

A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler.

We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power.

Interventions for increasing uptake in screening programmes.

Introduction: Opportunities for the early detection of disease are not sufficiently being taken advantage of. Specific interventions could increase the uptake of prevention programmes. A comprehensive analysis of effectiveness and cost-effectiveness of these interventions with reference to Germany is still needed.