We report high-sensitivity detection of 2,4,6-trinitrotoluene (TNT) by using laser photoacoustic spectroscopy where the laser radiation is obtained from a continuous-wave room temperature high-power quantum cascade laser in an external grating cavity geometry. The external grating cavity quantum cascade laser is continuously tunable over ≈400 nm around 7.3 μm and produces a maximum continuous-wave power of ≈200 mW. The IR spectroscopic signature of TNT is sufficiently different from that of nitroglycerine so that unambiguous detection of TNT without false positives from traces of nitroglycerine is possible. We also report the results of spectroscopy of acetylene in the 7.3-μm region to demonstrate continuous tunability of the IR source.

A strain-balanced, InP-based quantum cascade laser structure, designed for light emission at $4.6\mu \text{m}$ using a new nonresonant extraction design approach, was grown by molecular beam epitaxy. Removal of the restrictive two-phonon resonant condition, currently used in most structure designs, allows simultaneous optimization of several design parameters influencing laser performance. Following the growth, the structure was processed in buried heterostructure. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of $5\text{mm}\times 11.6\mu \text{m}$ . Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and $0.86\text{kA}/{\text{cm}}^2$ .

A strain-balanced, InP-based quantum cascade laser structure designed for light emission at $4.6\mu \mathrm{m}$ was grown by metal-organic chemical vapor deposition. A maximum total optical power of $1.6\mathrm{W}$ was obtained in continuous-wave mode at $300\mathrm{K}$ for uncoated devices processed in buried heterostructure geometry with stripe dimensions of $5\mathrm{mm}$ by $9.5\mu \mathrm{m}$ . Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and $1.05\mathrm{kA}∕{\mathrm{cm}}^2$ , respectively. Fully hermetically packaged laser of identical dimensions produced in excess of $1.5\mathrm{W}$ under the same conditions.

We report the sub-parts-per-billion-level detection of NO₂using tunable laser-based photoacoustic spectroscopy where the laser radiation is obtained from a room-temperature continuous-wave high-power quantum cascade laser operating in an external grating cavity configuration. The continuously tunable external grating cavity quantum cascade laser produces maximum single-frequency output of ≈300 mW tunable over ≈350 nm centered at 6.25 μm. We demonstrate minimum detection level of ≈0.5 parts per billion of NO₂in the presence of humidified air.

A strain-balanced, AlInAs/InGaAs/InP quantum cascade laser structure, designed for light emission near 9µm, was grown by molecular beam epitaxy. Laser devices were processed in buried heterostructure geometry. Maximum pulsed and continuous wave room temperature optical power of 4.5 and 2W and wallplug efficiency of 16% and 10%, respectively, were demonstrated for a 3mm by 10µm laser mounted epi-side down on an AlN/SiC composite submount. Pulsed laser characteristics were shown to be self-consistently described by a simple model based on rate equations using measured 70% injection efficiency for the upper laser level.

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