TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: PMA272 Tactical Aircraft Protection Systems

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: Investigate and develop new quantum cascade laser (QCL) architectures that enable scaling the laser brightness by a factor of five over current state-of-the-art single-element, single-mode QCLs.

DESCRIPTION: Single-element, edge-emitting quantum cascade lasers (QCLs) operating in the 4.5-5.0-micron wavelength region generally require a relatively narrow element width (~ 5-6 microns) to maintain stable, single-spatial-mode continuous wave (CW) operation up to the 1.5-2.0 watt-range output power levels. Higher CW output powers (~ 5 watts) have been achieved at the expense of multi-mode operation [Ref 1], as evidenced by unintended beam steering with increasing drive level [Ref 2], and more importantly, much degraded beam quality resulting in much lower brightness than that from a single-mode, diffraction-limited (M2 < 1.5) QCL with output power under 1.5 watts. It is very important to point out that for most, if not all, of the military applications based on the use of high-power lasers, such as Infrared Countermeasure (IRCM), the laser must have sufficient intensity (power per unit area) or power-in-the-bucket on target down range above the threshold value in order to achieve its intended effect [Refs 3, 4]. It is also worth noting that the achievable intensity is directly proportional to the laser beam brightness (not just laser power), which is a strong function of both the laser power and beam quality. To increase the laser intensity on target, effective modular approaches such as coherent beam combining or spectral beam combining [Refs 5, 6] can be used to scale up the power and also brightness of a laser array so long as the lasers in the array are near-beam-diffraction limited. Under this beam quality condition, both the power and brightness will scale linearly with the number of elements in the array.

The aforementioned beam combining approaches would directly benefit from increasing the available single-mode output brightness and power from the individual lasers to be combined. However, there is an upper limit on the power and brightness levels of a single QCL without degrading the beam quality for the following physical reasons: QCLs exhibit a maximum operating current density (Jmax) that is dependent on the injector doping level, but is typically in the range of 4-5 � the threshold current density, Jth. Thus, the maximum output power at Jmax is ultimately limited by the active-region volume, which is defined by the number of stages and the device area. Longer cavity length can be used to scale the area, although internal losses will generally limit the practical cavity lengths that can be used without incurring a significant reduction in slope efficiency. The number of active-region stages can be increased for optical gain, but are constrained by thermal-conductance considerations. Increasing the emitter width is limited by the onset of multi-spatial-mode operation, resulting in poor laser beam quality, as well as the effectiveness of heat removal in CW operation.

Single QCL power and brightness can be scaled up by increasing the wall-plug efficiency and improving its thermal management, both of which are active research areas. However, there is a third, equally important and yet unexplored development arena with high potential payoff in this brightness pursuit critical for the Naval applications, and which is the main focus of this topic. It is therefore the goal of this topic to investigate and develop new QCL architectures via judiciously increasing the active volume of the device, and thereby scaling the brightness by a factor of five over current state-of-the-art single-element, single-mode QCLs. These new architectures need to address strong self-heating in CW operation that results in thermal lensing that can trigger beam instabilities, like beam-steering and multi-mode operation. New methods for stabilizing the optical mode in CW operation without introducing significant penalty in optical loss and/or thermal conductance are required. In the near-infrared spectral region, many techniques have been demonstrated to stabilize the fundamental optical mode of single-element devices to high output powers [Refs 7, 8]. Many of these techniques, when judiciously and wisely adapted for QCLs, may benefit from reduced tolerances that scale with wavelength.

PHASE I: Develop and demonstrate feasibility of a QCL design around 4.5-micron wavelength, with no integrated linear or tapered amplifier, and with the brightness scaled up by a factor of 5 over buried hetero-structure devices with the current state-of-the-art brightness [Ref 9] that has achieved approximately 2 to 2.5 W room-temperature output power at 4.6 microns with an M2 value of ~1.06. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Demonstrate a single-mode QCL prototype that produces at least 10 W with M2 no more than 1.5 in both the fast and slow axes, and achieves a factor of 5 improvement in brightness under CW operation, based on the design developed in Phase I. The single QCL device should have no unexpected and undesirable beam steering effect as the QCL drive current is increased.

PHASE III DUAL USE APPLICATIONS: Fabricate, test, and finalize the technology based on the design and demonstration results developed during Phase II. Commercialize the technology for private sector use including law enforcement, marine navigation, commercial aviation enhanced vision, medical applications, and industrial manufacturing processing.

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. 98, 2011, 181102.� https://doi.org/10.1063/1.3586773

2. Bai, Y., Bandyopadhyay, N., Tsao, S., Selcuk, E., Slivken, S., and Razeghi, M. �Highly temperature insensitive quantum cascade lasers.� Appl. Phys. Lett. 97, 2010, 251104.� https://doi.org/10.1063/1.3529449

3. Sanchez-Rubio, A., Fan, T.Y., Augst, S.J., Goyal, A.K., Creedon, K.J., Gopinath, J.T., Daneu, V., Chann, B., and Huang, R. �Wavelength Beam Combining for Power and Brightness Scaling of Laser Systems.� Lincoln Laboratory Journal, 2014, Volume 20, Number 2, p. 52. https://www.ll.mit.edu/publications/journal/pdf/vol20_no2/20_2_3_Sanchez.pdf

4. Shukla, P., Lawrence, J., and Zhang, Y. �Understanding laser beam brightness: A review and new prospective in material processing.� Optics & Laser Technology 75, 2015, pp. 40�51. https://doi.org/10.1016/j.optlastec.2015.06.003

5. Hugger, S., Aidam, R., Bronner, W., Fuchs, F., Losch, R., Yang, Q., Wagner, J., Romasew, E., Raab, M., and Tholl, H.D. �Power scaling of quantum cascade lasers via multiemitter beam combining.� Optical Engineering, 2010, 49(11), p. 111111. https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-49/issue-11/111111/Power-scaling-of-quantum-cascade-lasers-via-multiemitter-beam-combining/10.1117/1.3498766.short

6. Huang, R.K., Chann, B., Burgess, J., Lochman, B., Zhou, W., Cruz, M., Cook, R., Dugmore, D., Shattuck, J., and Tayebati, P. �Teradiode's high brightness semiconductor lasers.� Proc. SPIE 9730, Components and Packaging for Laser Systems II, 97300C, 2016. doi: 10.1117/12.2218168

7. Huang, R.K., Donnelly, J.P., Missaggia, L.J., Harris, C.T., Plant, J., Mull, D.E., and Goodhue, W.D. �High-Power Nearly Diffraction-Limited AlGaAs�InGaAs Semiconductor Slab-Coupled Optical Waveguide Laser.� IEEE Phot. Tech. Lett, 15, 2003, 900. doi: 10.1109/LPT.2003.813406

8. Kintzer, E.S., Walpole, J.N., Chinn, S.R., Wang, C.A., and Missaggia, L.J. �High-Power, Strained-Layer Amplifiers and Lasers with Tapered Gain Regions.� IEEE Phot. Tech. Lett, 5, 1993, p. 605. doi: 10.1109/68.219683

9. Feng Xie, Catherine Caneau, Herve P. LeBlanc, Nick J. Visovsky, Satish C. Chaparala, Oberon D. Deichmann, Lawrence C. Hughes, Chung-en Zah, David P. Caffey, and Timothy Day, �Room Temperature CW Operation of Short Wavelength Quantum Cascade Lasers Made of Strain Balanced GaxIn1-xAs/AlyIn1-yAs
Material on InP Substrates,� IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, 2011, pp. 1445-1452.

KEYWORDS: QCL; Wall-Plug Efficiency; Thermal Load; Scaling; Mid-Wave Infrared; MWIR; Brightness