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We report the low threshold current density operation of strain-compensated In0.64Ga0.36As/In0.38Al0.62As quantum cascade lasers emitting near 4.94 mu m. By employing an enlarged strain-compensated structure and optimizing the injector doping density, a rather low threshold current density of 0.57 kA/cm(2) at 80K is achieved for an uncoated 20-mu m-wide and 2.5-mm-long laser.

We present a detailed study of lambda similar to 9.75 mu m GaAs/AIGaAs quantum cascade lasers. For a coated 2-mm-long and 40-mu m-wide laser, an optical power of 85 mu W is observed 95% duty cycle at 80 K. At a moderate driving pulse (1 kHz and 1% duty cycle), the device presents a peak power more than 20 mW even at 120 K. At 80 K, the fitted result of threshold current densities shows evidence of potential cw operation.

High-power operation of uncoated 22-mu m-wide quantum cascade lasers (QCLs) emitting at lambda approximate to 4.8 mu m is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated In0.68Ga0.32As/In0.37Al0.63As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64kA/cm(2). The effects of varying the cavity lengths from 1 to 4mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm(-1) is extracted.

We report low-threshold high-temperature operation of 7.4 μm strain-compensated InGaAs/InAlAs quantum cascade lasers (QCLs). For an uncoated 22- μm-wide and 2-mm-long laser, the low-threshold current densities, i.e. 0.33 kA/cm2 at 81 K in pulsed mode and 0.64 kA/cm2 at 84 K in cw mode, are realized. High-temperature operation of uncoated devices, with a high value of 223 K, is achieved in cw mode.

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 mu m above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60 mu m respectively, a peak output power more than 500 mW is achieved in pulsed mode operation. A low threshold current density J(th) = 2.6 kA/cm(2) gives the devices good lasing characteristics. In a drive frequency of 1 kHz, the laser operates up to 20% duty cycle.

We perform a three-dimensional numerical simulation based on a one-step chemical reaction model to investigate changes in the mode of H2-Air detonation wave propagation from rotating detonation wave (RDW) mode to standing detonation wave mode. The physical characteristics of an RDW with injection velocity of 500m/s are analyzed to investigate the physical mechanisms involved. We find that with increasing injection velocity, the detonation wave gradually changes from perpendicular to the head wall to parallel to the head wall. When the injection velocity exceeds the Chapman–Jouguet velocity VCJ (about 1984m/s), the detonation wave changes orientation to become perpendicular to the fuel injection direction, and the rotating mode changes accordingly to a standing mode. Finally, the plane detonation characteristic triple-wave structures can be found from the standing mode.