Dongxia Qu

Second-harmonic generation in quantum cascade lasers with electric field and current dependent nonlinear susceptibility

The authors demonstrate a quantum cascade laser design with an integrated resonant nonlinearity for second-harmonic generation. Its nonlinear power conversion efficiency is strongly dependent on the injected current density due to an electric field and current dependent nonlinear susceptibility. This dependence produces an observed tenfold increase of the conversion efficiency over the current density range of 2.7–7.5kA∕cm2. Furthermore, bidirectional lasing at widely different wavelengths is a side effect for this active region design.

A compact asymmetric chaotic optical cavity with long optical path lengths

We demonstrate an asymmetric multipass cavity with meter-scale optical path lengths in a volume of 68cm3 and diameter of 5.24cm. The cavity is machined from copper and coated with gold. For the characterization of the optical path length in the cavity, we perform a pulse-delay experiment by measuring the time delay between a laser pulse coupled into and out of the cavity. A midinfrared quantum cascade laser is employed as the source. By rotating the cavity, a variety of reentrant patterns and path lengths ranging from 2.0to6.0m can be obtained with straightforward optical alignment.

Tunability of notch angles in quantum cascade microlasers with highly deformed spiral resonators

We study the spectral characteristics of spiral-shaped micro-cylindrical quantum cascade lasers with various spiral geometries. With medium deformations and notch angles, our lasers can achieve single-mode emission with a side-mode suppression ratio over 30 dB.

Modeling and Design of a Highly Compact Chaotic Cavity for Optical Gas Sensing Applications

We present a novel class of compact, robust, and potentially cost-effective chaotic cavities for trace-gas sensing applications. The cavity consists of a single, closed, reflecting surface and can support up to 15.5 meter of optical path length with a cavity volume of only 68 cm3. The design is based on quasi-chaotic ray dynamics in a 3-dimensional (3-D) deformed sphere. Within the cavity, light traces out a quasi-stable trajectory that has been improved to achieve long optical path length and little beam overlap. The results show that the proposed chaotic cavity effectively refocuses the beam as the light bounces off the cavity wall. We modeled, fabricated, and tested a prototype cavity. The chaotic cavity can successfully achieve a 40-pass trajectory with a pulsed AlGalnP diode laser emitting at 661 nm. The experimental results agree well with calculations.

Quantum cascade microlasers with highly deformed spiral-resonators

We study the spectral characteristics of spiral-shaped micro-cylindrical quantum cascade lasers with various spiral geometries. With medium deformations and notch angles, our lasers can achieve single-mode emission with a side-mode suppression ratio over 30 dB.