OUSD (R&E) MODERNIZATION PRIORITY: Microelectronics; Hypersonics; Directed Energy TECHNOLOGY AREA(S): Weapons; Electronics; Air Platform 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 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 high performance, low Size, Weight, and Power (SWaP) fsDDLS capable of generating and sustaining filaments/plasma channels in the atmosphere ahead of a vehicle in hypersonic flight to reduce drag, heating, and displace shock. DESCRIPTION: This topic seeks the development of fsDDLS with SWaP appropriate for practical on board flight application and with sufficient energy deposition capability to effect drag reduction on a hypersonic vehicle via Laser filamentation. A fsDDLS has the potential to provide high (>70%) electrical-to-optical power conversion efficiency (PCE) in a relatively simple compact package vs. more complex Lasers (Fiber Lasers, Solid State Lasers, Gas Lasers, Diode Pumped Alkali Lasers, etc.). Two common approaches for achieving short pulse widths (taken as Full Width at Half Maximum (FWHM)) with laser diodes include gain switching, i.e. modulating the optical gain by switching the pump current, and mode locking. Mode-locked laser diodes can be external-cavity devices or monolithic devices and mode locking can be active, passive or a combination thereof. Ultimately, to achieve higher optical output power any design would involve some form of stacking or compact arrangement of individual diodes, with provision made for integrated cooling and temperature control. To achieve adequate optical output beam quality one would also expect a creative approach to combine, condition, and collimate output from the diode array. Approaches that rely on a fiber output would need to take into account pulse dispersion and other effects that might impact output quality. The end goal is a laser module with external access for power, control electronics, and thermal management (i.e. some means of controlled heat exchange that will not impact surrounding avionics and flight package), as well as an optical output port that could be configured for a specific application in Phase III that would involve generating optical filaments or plasma channels in the atmosphere. Femtosecond-laser plasmas form when atoms or molecules are ionized by high intensity laser pulses with widths on the order of tens to hundreds of femtoseconds (fs). The weak plasma is created via multiphoton ionization, where electrons absorb multiple photons to overcome the ionization potential of an atom or molecule. Filaments form when sufficient radiation is applied to cause self-focusing (Kerr effect) along the beam path. The filament is sustained by balancing self-focusing (Kerr effect) and defocusing (Kerr saturation) along the path to create a weak plasma channel in the transmission medium. If a filament is created in a hypersonic flow, additional energy can be deposited in the channel to displace gas and disrupt shockwaves in the hypersonic flow. In theory, a channel created by a vehicle mounted fsDDLS in hypersonic flight could reduce drag, heating, and displace shockwaves in a manner similar to an aero-spike. Laser aero-spikes have been studied in the past; however, in that case energy was concentrated at a point in the flow ahead of the target; whereas, a vehicle mounted fsDDLS could create a reduced density channel extending tens of meters (or more) ahead of the vehicle. Performance goals for system include: operation at a central wavelength of ~800 nm, with pulse duration around 50 fs to 200 fs, peak pulse power above 15 GigaWatts (GW), pulse energy greater than 5 millijoules, and average output power greater than 5 Watts, assuming a pulse repetition rate of 1 kHz. For demonstration purposes, a laser module that is roughly 50mm x 100mm x 25mm or smaller, with mass under 3 kg desired. In a hypersonic flight application, a fully developed module would need to be able to survive dynamic environments encountered by avionics and electronics carried in hypersonic flight and natural and manmade radiation environments that might be encountered at high altitude in a worst case scenario. PHASE I: Develop preliminary system design(s) with anticipated performance. Perform modeling, simulation and analysis (MS&A) and/or limited bench level testing to demonstrate the concept and an understanding of the technology. The proof of concept demonstration may be subscale and used in conjunction with MS&A results to verify scaling laws and feasibility. PHASE II: Complete a critical design and demonstrate the use of the technology in a table top/brass board prototype. Evaluate the effectiveness of the technology. Perform MS&A and characterization testing within the financial and schedule constraints of the program to show the level of performance achieved. If brass board achieved, government can provide independent test and characterization. Develop a plan for Phase III product design, fabrication, test and characterization. PHASE III DUAL USE APPLICATIONS: Incorporate lessons-learned from the Phase II prototype into a product design and fabricate/assemble a test unit. Work with government and/or government contractor to demonstrate product's performance improvement as compared to the state of the art. Work with government and/or government contractor to fully qualify the product for the intended application(s). Assist government and/or government contractor in integrating this product into a demonstrator system and assist with test and characterization. REFERENCES: S. Zeng, et.al, "Photonic integrated circuit based beam combining for future direct diode laser systems," Conference on Lasers and Electro-Optics, OSA Technical Digest (OSA, 2020), paper SF1O.6. https://www.osapublishing.org/abstract.cfm?URI=CLEO_SI-2020-SF1O.6 Benjamin D pke, et.al, Self-optimizing femtosecond semiconductor laser, Opt. Express (23)8, 9711-9716 (2015). Martin Hofmann, Mode-locked Diode Lasers from Microscopic Analysis to Femtosecond Pulses, Final Report, Grant No. FA9550-14-1-0137, 02/28/2018. (Search term: AFRL-AFOSR-UK-TR-2018-0027). Zhu, Y., "Hybridly Integrated Diode Lasers for Emerging Applications: Design, Fabrication, and Characterization" (2019). All Dissertations. 2510. https://tigerprints.clemson.edu/all_dissertations/2510 R go, I.S. et.al, Calculation of The Vehicle Drag and Heating Reduction at Hypervelocities with Laser-Induced Air Spike, J. Aerosp. Technol. Manag., S o Jos dos Campos, Vol.5, No 1, pp.43-48, Jan.-Mar., 2013. S. L. Chin, Some Fundamental Concepts of Femtosecond Laser Filamentation, Journal of the Korean Physical Society, Vol. 49, No. 1, July 2006, pp. 281-285. KEYWORDS: Direct Diode Laser System; DDLS; Femtosecond Semiconductor Laser; Femtosecond Direct Diode Laser; Femtosecond Diode Laser; Laser Filamentation; Laser Aero-Spike
