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Improved High-Power Performance in Fiber Laser Systems
Navy SBIR 2012.1 - Topic N121-068 NAVSEA - Mr. Dean Putnam - [email protected] Opens: December 12, 2011 - Closes: January 11, 2012 N121-068 TITLE: Improved High-Power Performance in Fiber Laser Systems TECHNOLOGY AREAS: Sensors, Electronics ACQUISITION PROGRAM: PMS 405, Directed Energy & Electric Weapon Systems Program Office, ACAT N/A RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected. OBJECTIVE: The objective of this effort is to greatly reduce nonlinear effects, such as Stimulated Brillouin Scattering (SBS), Four-Wave Mixing (FWM), and Stimulated Raman Scattering (SRS), to enable a simplified, robust, and reliable high-power fiber laser weapon. DESCRIPTION: The Navy is interested in two technical approaches that reduce nonlinear effects and increase laser power. One technical approach that has demonstrated effectiveness is to counter-pump the fiber amplifiers, to input the pump power at the exit of the fiber amplifier. This requires a fiber combiner capable of simultaneously handling both the pump power and the output power. Previous experiments of the counter-pump technology conducted have demonstrated fiber amplifiers in reverse pumping up to 1kW, with no nonlinear effects; however, the beam quality was only about 1.3 times the diffraction limit. To take advantage of laser capabilities it is important that they have beams which are as near the diffraction limit as possible, and thus can be focused to the smallest possible spot size. Thus an operational fiber laser weapon system must have a more nearly diffraction-limited beam, to improve beam quality and provide more tightly-focused energy on target. The second technical approach that has demonstrated effectiveness is the passive phase-locking of the fiber laser amplifiers, to produce a nearly diffraction-limited coherent output beam. The purpose of this effort is to develop the technologies of fiber laser amplifier counter-pumping to enable the realization of high power, high-quality, output beams. PHASE I: Phase I will include development of detailed modeling tools for analyzing the performance of fiber combiners for counter-pumping in passive phase-locking systems. The issues that impact and limit the performance of the fiber combiners will be identified. The results of the modeling will be used in Phase II to develop prototype combiner samples. The deliverables will be computer modeling tools and a report of the analysis results, discussing power scaling limits and expected performance in terms of beam quality and efficiency. The analysis should consider the practicalities of the material processing required to produce the fiber combiner. Options for fiber combiner fabrication for Phase II must be considered. The final report shall include the development plan, with performance goals and key milestones, for Phase II. PHASE II: In the first year, based upon the results of Phase I and the Phase II development plan, combiner samples will be fabricated and subjected to low power (a few hundred watts) evaluation. Careful measurements of the beam quality achievable will be made, along with thermal and splice performance data. In the second year, high-power combiners will be fabricated and evaluated at a level of 2 KW. Data on beam quality and thermal performance of the combiner and splices will be collected. The goals will be a reduction of beam quality to 1.1, and demonstrated operating times of 10 minutes or more at high power. The final report shall include all data collected, and a discussion of any remaining steps required to develop a high power shipboard demonstration. PHASE III: The contractor will support the transition of this effort to a shipboard laser system and will further develop the laser technology to support system integration for shipboard implementation. A shipboard laser system will likely be comprised of a number of these lasers which are coherently beam combined into a militarily useful power level. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The primary applications of counter-pumping at high power are defense related. However, the techniques employed in counter-pumping of fiber laser amplifiers can find use in applications such as high speed cutting and welding, broadband communication, and free space satellite data streaming. REFERENCES: 2. Sami Shakir, Bill Culver, Yuji Starcher, Burke Nelson, and George Bates, "Passive Phasing of a 4x4 Array of Fiber Amplifiers"; 10th Annual Directed Energy Symposium, Huntsville, AL, 3-5 Nov. 2007 3. S. Shakir, "Dynamic Characteristics of Passively Phased Fiber Amplifiers Arrays," in the Proceedings of the Solid-State Diode Laser Technology Review (SSDLTR), Albuquerque, NM. June 2008 4. S. Shakir, " Mode Locking of an Array of Fiber Lasers," in the Proceedings of the Solid-State Diode Laser Technology Review (SSDLTR), Newton, MA. June 2009 5. Erik Bochove and Sami A. Shakir, "Theory of Passively Phased Systems", IEEE JQE, vol.15, 320 (2009) KEYWORDS: Fiber Lasers;Stimulated Brillouin Scattering;High Power Lasers;Non-Linear Effects;Fiber Amplifiers;Counter Pumped Fiber Laser Amplifiers
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