The near-infrared transmission of a semiconductor multiple quantum well is probed under intense terahertz illumination. We observe clear evidence of the intraexcitonic Autler-Townes effect when the terahertz beam is tuned near the 1s-2p transition of the heavy-hole exciton. The strongly coupled effective two-level system has been driven with terahertz field strengths of up to 10  kV/cm resulting in a Rabi energy of ≈0.6 times the transition energy. The induced near-infrared spectral changes at low intensities are qualitatively explained using a basic two-level model.

We describe the fabrication and operation of surface emitting second-order distributed feedback quantum cascade ring lasers. The devices exhibit single-mode emission at a wavelength of 3.95μm with a side mode suppression ratio of 25dB. A linear tuning coefficient of 0.13cm−1∕K is observed. A single longitudinal mode in the ring shaped resonator results in a highly symmetric far-field pattern and a low beam divergence, represented by a full width at half maximum of ∼3°. Based on these characteristics the presented compact coherent light source may find its way into today’s midinfrared spectroscopy applications.

We report on the fabrication and operation of quantum cascade ring lasers providing grating-coupled surface emission. The devices exhibit tunable far fields, ranging from spot- to ring-shaped symmetric beam cross sections, depending on the grating period. This—along with threshold current densities as low as for comparable Fabry–Pérot lasers—demonstrates the compatibility of reduced beam divergence and two-dimensional integrability, resulting in an attractive light source for applications in midinfrared spectroscopy and imaging.

Articles you may be interested inDynamical Franz-Keldysh effect in GaAs/AlGaAs multiple quantum wells induced by single-cycle terahertz pulses Appl. Phys. Lett. 97, 211902 (2010); 10.1063/1.3518483 Strong enhancement of terahertz response in GaAs/AlGaAs quantum well photodetector by magnetic field Appl. Phys. Lett. 97, 022102 (2010); 10.1063/1.3462300Magnetoabsorption spectra of intraexcitonic transitions in GaAs-(Ga,Al)As semiconductor quantum wells Quasiphase matched surface emitting second harmonic generation in periodically reversed asymmetric GaAs/AlGaAs quantum well waveguide

Intervalley carrier transfer in short-wavelength InP-based quantum-cascade laser Appl. Phys. Lett. 93, 071109 (2008); 10.1063/1.2973212 Short-wavelength ( λ ≈ 3.05 μ m ) InP-based strain-compensated quantum-cascade laser Appl. Phys. Lett. 90, 051111 (2007); 10.1063/1.2437108 Short-wavelength ( λ ≈ 3.3 μ m ) InP-based strain-compensated quantum-cascade laserThe effect of doping concentration on the performance of short-wavelength quantum-cascade lasers based on the strain-compensated InGaAs/InAlAs/AlAs heterostructure on InP, emitting at 3.8 m, is investigated for average doping concentrations between 0.3 and 3.9ϫ 10 17 cm −3 ͑sheet densities between 1.6 and 20.9ϫ 10 11 cm −2 ͒. Although the threshold current density is rather independent of doping concentration, the maximum current density increases with doping and exhibits a saturation for the highest doping level. Other important performance characteristics such as differential quantum efficiency, peak optical emission power, slope efficiency, and maximum operating temperature are observed to be maximized for structures with an average doping of 2 − 3 ϫ 10 17 cm −3 , corresponding to a sheet density of about 1.5ϫ 10 12 cm −2 .

The authors report on a quantum well infrared detector embedded in a surface-plasmon waveguide and processed into a deeply etched photonic crystal structure. The device was characterized by collecting the polarization dependent response spectra at different angles of incidence. With this method it is possible to map the photonic band structure by directly detecting the modes of the photonic crystal. It therefore represents a new and direct characterization procedure for photonic crystals. The device shows a strong mixing between TE and TM polarized modes, which is caused by the asymmetric vertical waveguide design.

A monolithic coupling scheme in which two active waveguides merge into a single waveguide is presented for a GaAs∕AlGaAs quantum cascade laser. The evolving fields interfere and a constant phase is observed in the Y-shaped laser cavity, resulting in a far field pattern of a double slit. The mode distribution is comprehensively derived by matching the far field profiles to simulated values and shows a weak current dependence. The device demonstrates the feasibility of coherent laser resonators with prospective applications in interferometric sensing and high power laser arrays.

An inductively coupled plasma reactive ion etching process was developed for transferring patterns from a thin intermediate mask consisting of Ni or SiNx into GaAs. Smoothed out etch floors and sidewalls can be achieved under an approximately 200V bias by switching between an anisotropic etch phase and a deposition phase by gas chopping. The deposition of Si–O based film that protects the sidewall from chlorine attack is promoted by the addition of O2 to an SiCl4∕N2 gas mixture. The total achieved etch depth was approximately 20μm in this work, but the process can in principle be adopted for a larger depth and other chlorine-etchable III-V semiconductors. SiCl4 is shown to act as a suitable deposition gas as well as an etch gas.