We study the operation of an 8.5 µm quantum cascade laser based on GaInAs/AlInAs lattice matched to InP using three different simulation models based on density matrix (DM) and nonequilibrium Green's function (NEGF) formulations. The latter advanced scheme serves as a validation for the simpler DM schemes and, at the same time, provides additional insight, such as the temperatures of the sub-band carrier distributions. We find that for the particular quantum cascade laser studied here, the behavior is well described by simple quantum mechanical estimates based on Fermi's golden rule. As a consequence, the DM model, which includes second order currents, agrees well with the NEGF results. Both these simulations are in accordance with previously reported data and a second regrown device

We have significantly improved the energy resolution of a vacuum ultraviolet isochromat spectrometer for inverse photoemission spectroscopy. The detector is based on a Geiger–Müller counting tube with acetone as filling gas and a CaF2 entrance window working as an energy selective optical bandpass at a mean energy of 9.84eV. Under this operating conditions the detector achieves an optical energy resolution of 320meV (FWHM). By adding a gas chamber with two CaF2 windows at the entrance of the counting tube we are able to use absorption lines of oxygen and krypton to further enhance the optical resolution of the detector system. In the case of krypton the mean energy shifts to a somewhat lower value of 9.72eV. The energy resolution improves to about 115meV (FWHM), while the integrated sensitivity decreases to approximately 30%. Due to the ability to easily switch between high sensitivity and high resolution this new counting tube differs from other resolution-enhancing suggestions. Measurements on the prominent (n=1) image potential state on the Cu(111) surface indicate that the photon detector is no longer the major resolution limiting component in the spectrometer.

External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range. We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a broad gain spectrum and a resonantly driven micro-opto-electro-mechanical (MOEMS) scanner with an integrated diffraction grating in Littrow configuration. The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets, as well as on hazardous substances, such as explosives. Furthermore, different applications for the EC-QCL technology in spectroscopic sensing are presented. These include the fields of process analysis with on-or even inline capability and imaging backscattering spectroscopy for contactless identification of solid and liquid contaminations on surfaces. Recent progress in trace detection of explosives and related precursors in relevant environments as well as advances in food quality monitoring by discriminating fresh and mold contaminated peanuts based on their MIR backscattering spectrum is shown.Keywords: quantum cascade lasers; external cavity quantum cascade lasers; MOEMS grating; quantum cascade laser based spectroscopy; imaging laser backscattering spectroscopy; inline spectroscopic analysis

Abstract:We demonstrate spectral beam combining of a 980 nm tapered diode laser bar. The combined beam from 12 tapered emitters on the bar yielded an output power of 9.3 W at 30 A of operating current. An M 2 value of 5.3 has been achieved along the slow axis. This value is close to that of a free running single tapered emitter on the bar at the same current level. The overall spectral beam combining efficiency was measured to be 63%. ©2010 Optical Society of America

In situ process information in the chemical, pharmaceutical or food industry as well as emission monitoring, sensitive trace detection and biological sensing applications would increasingly rely on MIR-spectroscopic analysis in the 3 µm − 12 µm wavelength range. However, cost effective, portable, low power consuming and fast spectrometers with a wide tuning range are not available so far. To provide these MIR-spectrometer properties, the combination of quantum cascade lasers with a MOEMS scanning grating as wavelength selective element in the external cavity is addressed to provide a very compact and fast tunable laser source for spectroscopic analysis.