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Benzene is a gas known to be highly pollutant for the environment, for the water and cancerogenic for humans. In this paper, we present a sensor based on Quartz Enhanced Photoacoustic Spectroscopy dedicated to benzene analysis. Exploiting the infrared emission of a 14.85 µm quantum cascade laser, the sensor is working in an off-beam configuration, allowing easy alignment and stable measurements. The technique provides a very good selectivity to the sensor and a limit of detection of 30 ppbv in 1 s, i.e. a normalized noise equivalent absorption of 1.95 × 10−8 W.cm−1.Hz−1/2. The achieved performances of the sensor have enabled measurements on several air samples of a gas station showing a non-neglectable risk in case of long exposure.

Usually electromagnetic modes inside a laser resonator are a matter of the theoretical studies. In a sense we manage "to have a look into a whispering gallery mode (WGM) resonator" and observe how the resonator modes arrange in reality. The picture occurs to be quite different from the commonly used Bessel modes in a disk resonator. A chance to explore optical modes inside a resonator appears in a WGM laser with a cleaved cavity. The flat laser facet gives an opportunity to study both far and near field patterns formed by different modes. In this research we use a high resolution technique of detection of laser emission based on an atomic force microscope, which allowed us to visualize even high Q modes normally sealed inside the resonator. This information was completed with spatially resolved emission spectra and far-field patterns measured using an infrared camera. The analysis of the obtained results using both wave and geometrical optics approaches and finite elements simulations showed that emission of the studied devices is governed by a few low order optical modes experiencing a small number of reflections from the resonator walls. These modes can be considered as counter propagating Gaussian beams and their interference at the laser facet was also observed in the experiment. This work showed that, contrary to conventional ridge or surface emitting lasers, in such deformed disk resonators outputs of different optical modes are spatially separated and can be studied individually along the cleaved facet of the laser.

We demonstrate the high temperature operation, up to 80°C, of quantum cascade lasers emitting at a wavelength of 20 µm. The lasers are based on the InAs/AlSb materials and take benefit of a low loss plasmon-enhanced dielectric waveguide. The waveguide consists of doped InAs cladding layers and low-doped InAs spacers. For 2.9-mm-long devices, the threshold current density is 4.3 kA/cmsup2/supand the measured peak output power is 7 mW at room temperature. The cavity length dependence of the threshold currents also indicates that very large optical gain is achieved and effectively overcome the strong free carrier absorption.

We report on the growth, fabrication, experimental study and application in an absorption gas setup of distributed feed-back antimonide diode lasers with buried grating. First, half laser structures were grown by molecular beam epitaxy on GaSb substrates and stopped at the top of the waveguide. A second order Bragg grating was then defined by interferometric lithography on the top of the structure and dry etched by Reactive Ion Etching. The grating was, afterwards, buried thanks to an epitaxial regrowth of the top cladding layer. Finally, the wafer was processed using standard photolithography and wet etched into 10 µm-wide laser ridges. A single frequency laser emission around 2.3 µm was recorded, a maximum output power of 25 mW and a total continuous tuning range reaching 4.2 nm at fixed temperature. A device has been used to detect methane gas and shows strong potential for gas spectroscopy. This process was also replicated for a target of 3 µm laser emission. These devices showed an output power of 2.5 mW and a SMSR of at least 23 dB, with a 2.5 nm continuous tuning range at fixed temperature.