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We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW. [ABSTRACT FROM AUTHOR]

Optical power output is the most sought-after quantity in laser engineering. This is also true for quantum cascade lasers operating especially at long wavelengths. Buried heterostructure cascade lasers with epitaxial regrowth have typically shown the lowest loss due to high current confinement as well as superior lateral thermal conductivity at the expense of complexity and cost. Among the many factors affecting optical output are the widely used passivating materials such as Si3N4 and SiO2. These materials have substantial optical absorption in the long wavelength infrared, which results in optical loss reducing the output of the laser. In this letter, we report on quantum cascade lasers with various waveguide widths and cavity lengths using both PECVD grown Si3N4 and e-beam evaporated HfO2 as passivating material on the same structure. Their slope efficiency was measured, and the cavity losses for the two lasers were calculated. We show that HfO2 passivated lasers have approximately 5.5 cm−1 lower cavity loss compared to Si3N4 passivated lasers. We observe up to 38% reduction in lasing threshold current, for lasers with HfO2 passivation. We model the losses of the cavity due to both insulator and metal contacts of the lasers using Comsol Multiphysics for various widths. We find that the loss due to absorption in the dielectric is a significant effect for Si3N4 passivated lasers and lasers in the 8–12- $\mu \text{m}$ range may benefit from low loss passivation materials such as HfO2. Our results suggest that low-loss long wavelength quantum cascade lasers can be realized without epitaxial overgrowth. [ABSTRACT FROM AUTHOR]

We present theoretical calculations investigating the output power limitations of GaAs-based semiconductor lasers and the experimental results showing significant improvement of output power. To understand the influence of power limitation mechanisms, semiconductor laser with standard and unfolded cavity designs is studied. Our analysis reveals that an unfolded cavity laser enables more homogeneous longitudinal gain and intracavity optical intensity with reduced levels as compared with the standard cavity. Hence, an unfolded laser has theoretically lower power penalties induced by linear and nonlinear effects. For a 5.7-mm long laser cavity with 100- \mu \textm wide aperture, the experimental results demonstrate 21-W output from standard cavity whereas the unfolded cavity design achieves 33-W at 920 nm, which is >55% enhancement of the output, confirming the prediction of the theoretical calculations. The method represents a major step toward understanding semiconductor laser power limitations and realizing higher power output by control of longitudinal gain and power profiles. [ABSTRACT FROM PUBLISHER]

A study of the threshold characteristics of quantum-dot (QD) laser diodes shows how inhomogeneous broadening and p-doping influence the QD laser's temperature dependence of threshold To. The analysis includes the additional parameters of homogeneous broadening, quantum state populations, and threshold gain. The results show that while the source of negative T0 can occur due to different effects, the transparency current plays a critical role in both undoped and p-doped QD lasers. Experimental trends of negative To and their dependence on p-doping are replicated in the calculated results. Inhomogeneous broadening is found to play a lesser role to the transparency current in setting T0. Homogeneous broadening is most important for uniform QDs with thermally isolated ground-state transitions. [ABSTRACT FROM AUTHOR]