Y. Rouillard

Trace gas detection with antimonide-based quantum-well diode lasers

Widely tunable GaInAsSb/AlGaAsSb quantum well (QW) lasers have been grown by molecular beam epitaxy on GaSb substrates. Their emission wavelength, from 2.0 to 2.5 microm, make them suitable for the detection of many gas species in the wavelength range which corresponds to an atmospheric transmission window. Using these devices an experimental setup for open path gas detection has been developed.

Looking into the volcano with a Mid-IR DFB diode laser and Cavity Enhanced Absorption Spectroscopy

We report on the first application of extended-wavelength DFB diode lasers to Cavity-Enhanced Absorption Spectroscopy in-situ trace measurements on geothermal gases. The emission from the most active fumarole at the Solfatara volcano near Naples (Italy) was probed for the presence of CO and CH(4). After passing through a gas dryer and cooler, the volcanic gas flow (98% CO(2)) was analysed in real time for the concentration of these species, whose relatively strong absorption lines could be monitored simultaneously by a single Distributed Feed-Back (DFB) GaSb-based diode laser emitting around 2.33 mum (4300 cm(-1)) at room temperature. The concentrations were found to be about 3 ppm and 75 ppm, respectively, while actual detection limits for these molecules are around 1 ppb. We discuss the possibility of detecting other species of interest for volcanic emission monitoring.

Low-threshold GaInAsSb/AlGaAsSb quantum well laser diodes emitting near 2.3 µm

We report on low-threshold high-power quantum well diode lasers emitting near 2.3 µm based on the GaInAsSb/AlGaAsSb system. The threshold current density per quantum well is as low as 63 A cm−2. A maximum output power of 540 mW at 293 K in the continuous wave regime has been achieved.

Tunable-diode-laser spectroscopy of C 2 H 2 using a 3.03 μm GaInAsSb/AlGaInAsSb distributed-feedback laser

The mid-IR region beyond 3 microm is very attractive for gas sensing, since the fundamental absorption bands of several hydrocarbons are located in this range. We demonstrated, for the first time to our knowledge, the use of a novel GaInAsSb/AlGaInAsSb distributed-feedback laser emitting around 3.03 microm in a tunable-diode laser-spectroscopy application. The laser operates in continuous mode at room temperature with excellent single-mode and tuning properties. A comparison of the measurement results was made with the recently updated data on C212H(2) found in the HITRAN 2008 compilation. A good agreement was found between the measurements and the database. Wavelength modulation spectroscopy of acetylene at ambient conditions was made, and a sensitivity of 18 ppb (parts per billion) per meter at an integration time of 3 s corresponding to a relative absorption of 5 x 10(-6) was obtained. The optimum detection limit of the acetylene measurement in this wavelength modulation spectroscopy setup was better than 1.5 ppb m at an integration time of 600 seconds.

Low threshold high-power room-temperature continuous-wave operation diode laser emitting at 2.26 /spl mu/m

Diode lasers emitting at 2.26 /spl mu/m, based on the InGaAsSb-AlGaAsSb materials system, are reported. These devices exhibit high internal quantum efficiency of 78% and low threshold current density of 184.5 A/cm/sup 2/ for a 2-mm-long cavity. Output power up to 700 mW (/spl ap/550 mW) has been obtained at 280 K (300 K) in continuous-wave operation with 100 /spl mu/m/spl times/1 mm lasers. These devices have been coated with an antireflection on the output facet and are mounted epilayer down on a copper block. The working temperature was maintained by a thermoelectric Peltier cooling element.

Very-low-threshold 2.4-/spl mu/m GaInAsSb-AlGaAsSb laser diodes operating at room temperature in the continuous-wave regime

A GaInAsSb-AlGaAsSb large optical cavity triple-quantum-well structure was grown by molecular-beam epitaxy. Shallow mesa ridge-waveguide lasers with stripe width of 100 /spl mu/m were fabricated and tested. An internal losses coefficient as low as 4 cm/sup -1/ and a high internal quantum efficiency of 70% were obtained. In the pulsed regime at room temperature, the extrapolated threshold current densities for infinite cavity length is 78 A/cm/sup 2/. The threshold current density per quantum well is as low as 34 A/cm/sup 2/ for a 3-mm-long cavity.

Quartz enhanced photoacoustic spectroscopy with a 3.38 μm antimonide distributed feedback laser

A system for gas sensing based on the quartz-enhanced photoacoustic spectroscopy technique has been developed. It makes use of a quantum well distributed feedback (DFB) laser diode emitting at 3.38 μm. This laser emits near room temperature in the continuous wave regime. A spectrophone, consisting of a quartz tuning fork and two steel microresonators were used. Second derivative wavelength modulation detection is used to perform low concentration measurements. The sensitivity and the linearity of the Quartz enhanced photoacoustic spectroscopy (QEPAS) sensor were studied. A normalized noise equivalent absorption coefficient of 4.06×10(-9) cm(-1)·W/Hz(1/2) was achieved.

Laser Diodes for Gas Sensing Emitting at 3.06

Type-I quantum-well laser diodes with an active region constituted of GaInAsSb-AlGaInAsSb are reported. Broad-area lasers have demonstrated a threshold current density of 255 A/cm2 at room temperature. Distributed-feedback lasers have been operated in the continuous-wave regime at 20°C with a wavelength of 3.06 μm, a threshold current of 54 mA, and an output power of 6 mW.

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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.

m at Room Temperature

Optical transitions in Ga0.35In0.65As0.32Sb0.68/Al0.25Ga0.50In0.25As0.24Sb0.76 quantum wells grown by molecular beam epitaxy on GaSb substrates have been detected by photoreflectance. Based on comparison with energy level calculations, the chemical conduction band offset ratio has been determined to be 78%. This translates into 65% in the real structure (i.e., after strain inclusion) which is an evidence of the expected band offset ratio modification in a quinary barrier system in favor of enhanced confinement in the valence band, when compared to similar quantum wells but with quaternary barriers. This has allowed us to explain the main photoluminescence thermal quenching mechanisms and connect the carrier activation energies with delocalization of excitons at low temperatures and the escape of holes via the confined states ladder at room temperature.