Two terahertz quantum cascade lasers based on GaAs∕Al0.1Ga0.9As heterostructures are reported. Pulsed mode operation up to 84K and continuous wave (cw) power of 0.36mW at 10K are demonstrated for the laser which emits from 1.34to1.58THz. The other laser shows emission from 1.2to1.32THz with pulsed mode operation up to 69K and cw power of 0.12mW at 10K.

In this paper we review recent progress in obtaining laser action from semiconductor quantum cascade structures covering the low THz region of the electromagnetic spectrum, from 2 THz (λ 155 μm) down to the sub-THz region (λ > 300 μm). Particularly, laser active region designs based on bound-to-continuum transition and magnetically assisted intra-well transition are presented. The wide scalability of active region designs is discussed and illustrated with experimental data. Latest results including the demonstration of laser action from quantum heterostructure at 950 GHz are presented.THz quantum cascade lasers are based on semiconductor heterostructures and cover a wide spectral window which now extends below 1 THz.

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Lasers based on microcavities are extremely attractive for their compactness, low power dissipation, and potential for ultrafast modulation speed. We describe an ultrasmall laser based on a subwavelength electronic inductor-capacitor (LC) resonant circuit that allows for extreme confinement of the electric field. This electrically injected laser operates at a frequency of 1.5 terahertz, and the mode volume is strongly subwavelength. The design concept of the LC resonator can be extended from the terahertz range to higher frequencies and also applied to detectors and modulators.

Although lasers have found numerous applications, their design is often still based on the concept of a gain medium within a mirror cavity. Exceptions to this are distributed feedback lasers(1), in which feedback develops along a periodic structure, or random lasers, which do not require any form of cavity(2). Random lasers have very rich emission spectra, but are difficult to control. Distributed feedback devices, conversely, have the same limited design possibilities of regular lasers. We show, by making use of a quasi-crystalline structure in an electrically pumped device, that several advantages of a random laser can be combined with the predictability of a distributed feedback resonator. We have constructed a terahertz quantum cascade laser based on a Fibonacci distributed feedback sequence, and show that engineering of the self-similar spectrum of the grating allows features beyond those possible with traditional periodic resonators, such as directional output independent of the emission frequency and multicolour operation