TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: JSF Joint Strike Fighter

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop novel quantum cascade laser device structures to reduce the thermal impedance significantly (i.e., by at least a factor of two).

DESCRIPTION: High-performance, midwave-infrared (MWIR) (~4.5-5um) quantum cascade lasers (QCLs) have been reported with front-facet continuous wave (CW) output powers as high as ~ 5W from optimized facet-coated, single-element devices mounted on diamond heatsinks [Ref 1]. A primary and yet very critical technical challenge in deploying higher performance and reliable QCLs for Naval applications is to address and resolve the problems of excessive heat generation within the QCL active region. This is caused by two fundamental aspects of the QCL: low wall-plug efficiency and very high thermal impedance. This SBIR topic is to address the second, critical issue of QCLs� high thermal impedance, which remains an Achilles' heel for QCLs that adversely impacts the performance and reliability of high power QCLs.

It has been documented [Ref 1] that QCLs� internal device heating is an order of magnitude larger than for conventional near-IR diode lasers, and that QCL performance is a strong function of the active region temperature rise. High efficiency active region designs can be employed to minimize heat generation, but even the best state-of-the-art QCLs at present still generate about 5-10 times the heat load of near-IR interband-transition semiconductor lasers. Hence, the extreme heating of QCLs combined with their inherently high thermal impedance of the superlattice (SL) structures of the active regions leads to catastrophic facet failure, most likely caused by thermally-induced shear stress [Ref 2]. Heat flux within a QCL can exceed kW/cm2 out of the active region in the semiconductor, and its limited intrinsic ability to dissipate that heat limits the range of operating power and the maximum lifetimes. For instance, at Watt-range CW output powers, the dissipated heat typically exceeds 20 W and poses severe challenges for field compatible packaging with sufficient thermal management. Furthermore, self-heating under CW operation aggravates active-region carrier leakage, which degrades device performance (i.e., lower slope efficiency and increased threshold current).

The Navy seeks innovative, monolithic QCL device structures to reduce a QCL�s effective thermal impedance in the direction vertical to the epitaxial layers significantly (by at least a factor of two), relative to the state-of-the-art. The device structure should also be capable of emitting at least 5W continuous wave output at room temperature with emission wavelength at ~4.5 um and near diffraction-limited beam quality (M2 < 1.5). Moreover, microscopic-physics-based heat models are also needed to elucidate interfacial contributions to thermal resistance and guide the design of reduced overall device thermal resistance. It is anticipated that a factor of two to three improvement in thermal resistance would allow for a dramatic decrease in self-heating and subsequent enhanced device performance and reliability, especially at high output powers. Successful combined development of substantially improved QCLs� thermal resistance in this SBIR topic and the 40% wall-plug efficiency in another Navy program would finally realize the vision of enabling improvement of the overall size and weight of QCL packaging and its active cooling system, and the associated reliability by up to a factor of 10. Successful completion of this project and the QCL efficiency program will be the most significant landmark achievements for the QCL in the last 15 years and will ultimately elevate the performance, size and weight, and operating lifetimes of QCL to their theoretical limits.

PHASE I: Develop a novel QCL device structure model through which the effective thermal impedance in the direction vertical to the epitaxial layers could be feasibly reduced by at least a factor of two, relative to the state-of-the-art. Demonstrate that the device structure is feasibly capable of emitting at least 5W continuous wave output at room temperature with emission wavelength at ~4.5 um and near diffraction-limited beam quality (M2 < 1.5). Produce plans to develop a prototype under Phase II.

PHASE II: Fabricate and demonstrate a developed QCL device prototype that produces reduced thermal impedance and ~4.5 um emission with at least 5W continuous wave output at room temperature and near diffraction-limited beam quality (M2 < 1.5).

PHASE III DUAL USE APPLICATIONS: Fully develop and transition high-performance QCLs with high thermal conductance for DoD applications in the areas of Directed Infrared countermeasures (DIRCMs), advanced chemicals sensors, and Laser Detection and Ranging (LIDAR). The DoD has a need for advanced, compact, high-performance MWIR QCL arrays with high thermal impedance of which the output power can readily be scaled via beam combining for current and future generation DIRCMs, LIDARs, and chemicals/explosives sensing. The commercial sector can also benefit from this crucial, game-changing technology development in the areas of detection of toxic gases, environmental monitoring, and non-invasive health monitoring and sensing.

REFERENCES:

1. Bai, Y., Bandyopadhyay, N., Tsao, S., Slivken, S. and Razeghi, M. �Room temperature quantum cascade lasers with 27% wall plug efficiency.� Appl. Phys. Lett. 2011, 98, 181102, doi: 10.1063/1.3586773

2. Zhang, Q., Liu, F., Zhang, W., Lu, Q., Wang, L., Li, L., and Wang, Z. �Thermal induced facet destructive feature of quantum cascade lasers.� Appl. Phys. Lett. 2010, 96, 141117. https://doi.org/10.1063/1.3385159

KEYWORDS: Quantum Cascade Lasers; Thermal Impedance; Thermal Resistance; Midwave-infrared; Wall-plug Efficiency; Laser Array