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We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/AlGaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 microm is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup.

We report on the realization of second-order distributed feedback quantum-cascade lasers at λ=9.35 μm, where the active region consists of GaAs, AlGaAs, and strained InGaAs grown on GaAs. A metal-stripe surface grating structure allows a high surface emission efficiency for the TM-polarized light. The emitted power via the surface is in the range of 100 mW and exceeds the emitted power from one facet. A double-lobed surface-emission far-field pattern is obtained for the lasing mode. The single-mode emission wavelength is continuously tunable by the heat sink temperature.

In this letter, the influence of metal films and dielectric waveguides on the radiation characteristics of light emitting diodes (LEDs) is investigated. Cross and hexagonal surface grating structures are used to excite surface plasmons and waveguide modes in these media. A beam divergence as small as 17° is achieved for a hexagonal grating coated with a 40 nm Ag film. The maximum quantum efficiency is found for a hexagonal grating with a 10-nm-thick Au film and a 250-nm-thick dielectric layer. The optical power emitted by this LED into the solid angle from −30° to 30° is 10% higher than that of an LED without metal film and dielectric layer.

We report the realization of an injection laser based on intraband transitions in a finite AlGaAs/GaAs superlattice. The active material is a 30 period sequence of injectors/active regions made from AlGaAs/GaAs quantum wells. By an applied electric field, electrons are injected into the second miniband of a chirped superlattice and relax radiative to the lowest miniband. At a heat-sink temperature of 10 K, the laser emission wavelength is 12.9 μm with peak optical powers exceeding 100 mW and a threshold current density of 9.8 kA/cm2. The maximum operating temperature is 50 K. For this device, a waveguide consisting of heavily doped GaAs cladding and low doped core layers has been used as a plasma-enhanced confinement.