High Power Thermoelectrically Cooled and Uncooled Quantum Cascade Lasers With Optimized Reflectivity Facet Coatings

We present a method of preserving the device wall-plug efficiency by adjusting mirror losses with facet coatings for longer cavity quantum cascade lasers. An experimental study of output power and wall-plug efficiency as functions of mirror losses was performed by varying the front facet coating reflectivity with a high-reflectivity-coated rear facet. The use of optimized reflectivity coatings on 7-mm-long chips resulted in continuous-wave output power of 2.9 W at 293 K for thermoelectrically cooled devices mounted on AlN submounts and average and continuous-wave output power in excess of 1 W for uncooled devices emitting at 4.6 µm.Engineering and Applied Science

3 W Continuous-Wave Room Temperature Single-Facet Emission From Quantum Cascade Lasers Based On Nonresonant Extraction Design Approach

A strain-balanced, InP-based quantum cascade laser structure, designed for light emission at 4.6 $\mu$m using a new nonresonant extraction design approach, was grown by molecular beam epitaxy. Removal of the restrictive two-phonon resonant condition, currently used in most structure designs, allows simultaneous optimization of several design parameters influencing laser performance. Following the growth, the structure was processed in buried heterostructure. Maximum single-ended continuous-wave optical power of 3 W was obtained at 293 K for devices with stripe dimensions of 5 mm 11.6 $\mu$m. Corresponding maximum wallplug efficiency and threshold current density were measured to be 12.7% and 0.86 kA/cm$^{2}$.Physic

Towards 20-Watt Continuous Wave Quantum Cascade Lasers

Significant increase in continuous wave optical power from a single quantum cascade laser (QCL), beyond its current record of 5W, will likely require power scaling with active region lateral dimensions. Active region overheating presents a major technical problem for such broad area devices. Laser thermal resistance can be reduced and laser self-heating can be suppressed by significantly reducing active region thickness, i.e. by reducing number of active region stages and by reducing thickness of each stage in the cascade. The main challenge for quantum cascade lasers with a thin active region is to ensure that optical power emitted per active region unit area stays high despite the reduction in active region thickness, a condition critical for the power scaling. Experimental data demonstrating a multi-watt continuous wave operation for broad area QCLs, as well as various aspects of bandgap engineering, waveguide design, and thermal design pertinent to the broad area configuration, are discussed in this manuscript. The critical differences in broad-Area laser design between mid-wave and long-wave QCLs is highlighted. Finally, semi-empirical model projections showing that the goal of reaching 20W from a single emitter is realistic is presented

Continuous wave operation of buried heterostructure 4.6 µm quantum cascade laser Y-junctions and tree arrays.

Room-temperature continuous-wave operation for buried heterostructure 4.6 µm quantum cascade laser Y-junctions and tree arrays, overgrown using hydride vapor phase epitaxy, has been demonstrated. Pulsed wall plug efficiency for the Y-junctions with bending radius of 5mm was measured to be very similar to that of single-emitter lasers from the same material, indicating low coupling losses. Comparison between model and experimental data showed that the in-phase mode was dominating for 10mm-long Y-junctions with 5 µm-wide 1mm-long stem and 5 µm-wide branches. Total optical power over 1.5 W was demonstrated for four-branch QCL tree array

Continuous wave operation of buried heterostructure 4.6 µm quantum cascade laser Y-junctions and tree arrays.

Room-temperature continuous-wave operation for buried heterostructure 4.6 µm quantum cascade laser Y-junctions and tree arrays, overgrown using hydride vapor phase epitaxy, has been demonstrated. Pulsed wall plug efficiency for the Y-junctions with bending radius of 5mm was measured to be very similar to that of single-emitter lasers from the same material, indicating low coupling losses. Comparison between model and experimental data showed that the in-phase mode was dominating for 10mm-long Y-junctions with 5 µm-wide 1mm-long stem and 5 µm-wide branches. Total optical power over 1.5 W was demonstrated for four-branch QCL tree array

Continuous Wave Power Scaling In High Power Broad Area Quantum Cascade Lasers

Experimental and model results for high power broad area quantum cascade lasers are presented. Continuous wave power scaling from 1.62 W to 2.34 W has been experimentally demonstrated for 3.15 mm-long, high reflection-coated 5.6 μm quantum cascade lasers with 15 stage active region for active region width increased from 10 μm to 20 μm. A semi-empirical model for broad area devices operating in continuous wave mode is presented. The model uses measured pulsed transparency current, injection efficiency, waveguide losses, and differential gain as input parameters. It also takes into account active region self-heating and sub-linearity of pulsed power vs current laser characteristic. The model predicts that an 11% improvement in maximum CW power and increased wall plug efficiency can be achieved from 3.15 mm x 25 μm devices with 21 stages of the same design but half doping in the active region. For a 16-stage design with a reduced stage thickness of 300Å, pulsed roll-over current density of 6 kA/cm2, and InGaAs waveguide layers; optical power increase of 41% is projected. Finally, the model projects that power level can be increased to ∼4.5 W from 3.15 mm × 31 μm devices with the baseline configuration with T0 increased from 140 K for the present design to 250 K

Two Wavelength Operation Of An Acousto-Optically Tuned Quantum Cascade Laser And Direct Measurements Of Quantum Cascade Laser Level Lifetimes

We report simultaneous two wavelength operation of an acousto-optically tuned quantum cascade laser (QCL). The two wavelengths can be independently tuned as well as independently switched, retaining the submicrosecond switching capability. In addition, we have used the two wavelength operation as a tool for the direct measure of the lifetimes of the lasing states in a practical QCL. The lifetime measurements in an operational QCL are facilitated by our ability to vary the frequency separation between two simultaneously lasing wavelengths. The measured lifetime is 0.6 ps ± 0.2 ps for our quantum cascade laser. The two wavelength operation of QCLs paves the way for time resolved pump/probe studies of infrared phenomena and provides direct insight into the effectiveness of various QCL structure designs