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We present the first evidence for a distinct optical phonon progression in the linear and nonlinear intersubband absorption spectra of electrons in a GaN/Al(0.8)Ga(0.2)N heterostructure. Femtosecond two-color pump-probe experiments in the midinfrared reveal spectral holes on different vibronic transitions separated by the LO-phonon frequency. These features(More)
We present a detailed theoretical analysis for the determination of the total internal loss in Fabry-Perot resonators based on Fourier analysis of the emission or transmission spectrum. The observation of higher-order harmonics and their relative height in the Fourier-transformed spectrum allow us to quantify the total resonator loss. Because this new(More)
INTRODUCTION Purpose of the present study was to evaluate the Lake Louise acute mountain sickness (AMS) score questionnaire at different altitudes and to compare it with the currently used clinical score and the environmental symptoms questionnaire AMS-C score. METHODS We investigated 490 climbers who stayed over night at 4 huts in the Swiss Alps, located(More)
Continuous wave operation of quantum cascade lasers is reported up to a temperature of 312 kelvin. The devices were fabricated as buried heterostructure lasers with high-reflection coatings on both laser facets, resulting in continuous wave operation with optical output power ranging from 17 milliwatts at 292 kelvin to 3 milliwatts at 312 kelvin, at an(More)
OBJECTIVE To evaluate the therapeutic efficacy of a portable hyperbaric chamber for treatment of acute mountain sickness. DESIGN Controlled randomised trial over two mountaineering seasons. SETTING High altitude research laboratory at 4559 m above sea level. SUBJECTS 64 climbers with acute mountain sickness randomly allocated to different treatments.(More)
We present photoacoustic (PA) spectroscopy measurements of carbon dioxide, methanol, and ammonia. The light source for the excitation was a single-mode quantum cascade distributed-feedback laser, which was operated in pulsed mode at moderate duty cycle and slightly below room temperature. Temperature tuning resulted in a typical wavelength range of(More)
In this Letter, we report the tuning of the emission wavelength of a single mode distributed feedback quantum cascade laser by modifying the mode effective refractive index using fluids. A fabrication procedure to encapsulate the devices in polymers for microfluidic delivery is also presented. The integration of microfluidics with semiconductor laser(More)
The frequency noise properties of commercial distributed feedback quantum cascade lasers emitting in the 4.6 μm range and operated in cw mode near room temperature (277 K) are presented. The measured frequency noise power spectral density reveals a flicker noise dropping down to the very low level of <100 Hz(2)/Hz at 10 MHz Fourier frequency and is globally(More)
The possible importance of zinc-oxide-based optoelectronic devices is reviewed in this paper, which places special emphasis on the need to achieve p-type ZnO. ABSTRACT | ZnO is an attractive material for applications in electronics, photonics, acoustics, and sensing. In optical emitters, its high exciton binding energy (60 meV) gives ZnO an edge over other(More)
The effects on surface morphology, crystal quality, and growth rate of undoped AlN layers grown on c-plane sapphire substrates due to the changes in growth parameters, such as V-III ratio, N 2-H 2 ratio, and growth temperature in LP-MOVPE are studied here. The optimized growth process resulted in an almost flat surface morphology with a significantly(More)