Matthew Suttinger

5.6 μm quantum cascade lasers based on a two-material active region composition with a room temperature wall-plug efficiency exceeding 28%

5.6 μm quantum cascade lasers based on the Al0.78In0.22As/In0.69Ga0.31As active region composition with the measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured for the design by testing devices with variable cavity lengths. A threshold current density of 1.7 kA/cm2 and a slope efficiency of 4.9 W/A were measured for uncoated 3.15 mm × 9 μm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288 K to 348 K for the structure can be described by characteristic temperatures T0 ∼ 140 K and T1 ∼ 710 K, respectively.

Power scaling and experimentally fitted model for broad area quantum cascade lasers in continuous wave operation

Abstract. Experimental and model results for 15-stage broad area quantum cascade lasers (QCLs) are presented. Continuous wave (CW) power scaling from 1.62 to 2.34 W has been experimentally demonstrated for 3.15-mm long, high reflection-coated QCLs for an active region width increased from 10 to 20  μm. A semiempirical model for broad area devices operating in CW 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 sublinearity of pulsed power versus 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×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 300 Å, pulsed rollover current density of 6  kA/cm2, and InGaAs waveguide layers, an 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.

Room temperature operation of quantum cascade lasers monolithically integrated onto a lattice-mismatched substrate

Experimental data for an InP-based 40-stage quantum cascade laser structure grown on a 6-in. GaAs substrate with a metamorphic buffer are reported. The laser structure had an Al0.78In0.22As/In0.73Ga0.27As strain-balanced active region composition and an 8 μm-thick, all-InP waveguide. High reflection coated 3 mm × 30 μm devices processed from the wafer into a ridge-waveguide configuration with a lateral current injection scheme delivered over 200 mW of total peak power at 78 K with lasing observed up to 170 K. No signs of performance degradation were observed during a preliminary 200-min reliability testing. Temperature dependence for threshold current and slope efficiency in the range from 78 K to 230 K can be described with characteristic temperatures of T0 ≈ 460 K and T1 ≈ 210 K, respectively. Lasing was extended to 303 K by applying a partial high reflection coating to the front facet of the laser.

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.

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.

High performance 40-stage and 15-stage quantum cascade lasers based on two-material active region composition

5.6μm quantum cascade lasers based on Al0.78In0.22As/In0.69Ga0.31As active region composition with measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured by testing devices with variable cavity length. Threshold current density of 1.7kA/cm2 and slope efficiency of 4.9W/A were measured for uncoated 3.15mm x 9µm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288K to 348K can be described by characteristic temperatures T0~140K and T1~710K, respectively. Pulsed slope efficiency, threshold current density, and wallplug efficiency for a 2.1mm x 10.4µm 15-stage device with the same design and a high reflection-coated back facet were measured to be 1.45W/A, 3.1kA/cm2 , and 18%, respectively. Continuous wave values for the same parameters were measured to be 1.42W/A, 3.7kA/cm2 , and 12%. Continuous wave optical power levels exceeding 0.5W per millimeter of cavity length was demonstrated. When combined with the 40-stage device data, the inverse slope efficiency dependence on cavity length for 15-stage data allowed for separate evaluation of the losses originating from the active region and from the cladding layers of the laser structure. Specifically, the active region losses for the studied design were found to be 0.77cm-1, while cladding region losses – 0.33cm-1. The data demonstrate that active region losses in mid wave infrared quantum cascade lasers largely define total waveguide losses and that their reduction should be one of the main priorities in the quantum cascade laser design.

High performance 5.6μm quantum cascade lasers

5.6 μm quantum cascade lasers based on Al 0.78 In 0.22 As/In 0.69 Ga 0.31 As active region composition with measured pulsed room temperature wall plug efficiency of 28.3% are reported. Injection efficiency for the upper laser level of 75% was measured for the new design by testing devices with variable cavity length. Threshold current density of 1.7kA/cm2 and slope efficiency of 4.9W/A were measured for uncoated 3.15mm × 9μm lasers. Threshold current density and slope efficiency dependence on temperature in the range from 288K to 348K for the new structure can be described by characteristic temperatures T0 ~ 140K and T1 ~710K, respectively. Experimental data for inverse slope efficiency dependence on cavity length for 15-stage quantum cascade lasers with the same design are also presented. When combined with the 40-stage device data, the new data allowed for separate evaluation of the losses originating from the active region and from the cladding layers of the laser structure. Specifically, the active region losses for the studied design were found to be 0.77 cm-1, while cladding region losses - 0.33 cm-1. The data demonstrate that active region losses in mid wave infrared quantum cascade lasers largely define total waveguide losses and that their reduction should be one of the main priorities in the quantum cascade laser design.

Image reconstruction and target acquisition through compressive sensing

Compressive imaging is an emerging field which allows one to acquire far fewer measurements of a scene than a standard pixel array and still retain the information contained in the scene. One can use these measurements to reconstruct the original image or even a processed version of the image. Recent work in compressive imaging from random convolutions is extended by relaxing some model assumptions and introducing the latest sparse reconstruction algorithms. We then compare image reconstruction quality of various convolution mask sizes, compression ratios, and reconstruction algorithms. We also expand the algorithm to derive a pattern recognition system which operates of a compressively sensed measurement stream. The developed compressive pattern recognition system reconstructions the detections map of the scene without the intermediate step of image reconstruction. A case study is presented where pattern recognition performance of this compressive system is compared against a full resolution image.