Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 µm-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M2 < 1.2 up to 1 W for ∼5 µm-wide ridges. 5 µm-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of ∼1.25 cm over a distance of 100 m.
Heteroepitaxial growth of orientation-patterned (OP) GaP (OP-GaP) on wafer-bonded OP-GaAs templates is investigated by low-pressure hydride vapor phase epitaxy for exploiting the beneficial low two-photon absorption properties of GaP with the matured processing technologies and higher-quality substrates afforded by GaAs. -First, GaP homoepitaxial selective area growth (SAG) is conducted to investigate the dependence of GaP SAG on precursor flows and temperatures toward achieving a high vertical growth rate and equal lateral growth rate in the [110] and [110]-oriented openings. Deteriorated domain fidelity is observed in the heteroepitaxial growth of OP-GaP on OP-GaAs due to the enhanced growth rate on domain boundaries by threading dislocations generated by 3.6% lattice matching in GaP/GaAs. The dependence of dislocation dynamics on heteroepitaxial growth conditions of OP-GaP on OP-GaAs is studied. High OP-GaP domain fidelity associated with low threading dislocation density and a growth rate of 57 μm h À1 are obtained by increasing GaCl flow. The properties of heteroepitaxial GaP on semi-insulating GaAs is studied by terahertz time-domain spectroscopy in the terahertz range. The outcomes of this work will pave the way to exploit heteroepitaxial OP-GaP growth on OP-GaAs for frequency conversion by quasi-phase-matching in the mid-infrared and terahertz regions.
We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 µm, a novel-geometry device that can scale the output power while maintaining good beam quality. Buriedridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth -the tapered region scales the output power, while the emitting facet is located at the narrowend taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M 2 ) measurements along with beam-stability measurements were performed -a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M 2 values close to 1 up to ∼1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation.
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