TECHNOLOGY AREAS: Electronics, Weapons

ACQUISITION PROGRAM: PMS 405 Laser Weapon System (fiber laser) Program. ACAT leve N/A

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop and evaluate an affordable design for a fiber laser and/or a fiber laser amplifier suitable for eventual military applications.

DESCRIPTION: The present technology of high-power fiber lasers is based on Yb-doped silica fibers, operating in the wavelength region around 1050 nm. Commercial, diffraction-limited, single-fiber devices with power levels of 3 kW are commercially available and higher-power devices at the 5-kW level are under development, for industrial applications such as cutting and welding. The high-power fiber-laser technology is of interest for the Navy in directed energy systems, but the wavelength of operation of Yb-doped fibers presents significant operational problems related to eye safety. Fiber lasers at wavelengths longer than 1400 nm have greatly reduced problems of eye safety, but development of kW-level and higher power lasers is well behind that of the Yb-doped systems. One important question is the ultimate limit to the single-fiber, diffraction-limited eyesafer sources, which may be, in some combination, due to optical damage, other nonlinear effects, or thermal effects. In some cases fundamental data to help determine these limits is lacking for the eyesafer wavelengths, and thus measurements are required. Once the limit is found, one can proceed to design a high-power system that can generate power at some safe fraction of the limit, and test the design through construction and operation of a sub-scale device. Both lasers per se, and laser amplifiers (broad band) are of interest.

PHASE I: Investigate the possible limits to the power output of diffraction-limited, single-fiber, eyesafer fiber lasers and laser amplifiers, through theoretical analysis as well as experiments to verify key parameters needed for the analysis. Develop a preliminary design for a high-power system that approaches these limits, and would be suited for military applications. Both single lasers as well as beam combining of broad band laser amplifiers should be addressed.

PHASE II: Utilize the findings established in Phase I to further develop a single-fiber, diffraction limited eyesafer fiber laser that produces power set only by the limits determined in Phase I. Conduct further experimental measurements of key fiber parameters as necessary. Design, build and deliver a credible, brassboard, sub-scale fiber laser that evaluates the design. This brassboard would be anticipated to deliver powers of the order of kilowatts.

PHASE III: Design, build and test a full-scale, eyesafer fiber-laser system brassboard to demonstrate that the design and subscale testing is valid. Deliver the system for testing with respect to effects and propagation.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Many of the machining applications for high-power fiber lasers are wavelength insensitive and if the eyesafer fiber laser can ultimately produce higher powers than current Yb-doped, single-fiber, diffraction-limited systems, the technology developed can find uses in a number of industrial materials-processing applications. In addition, the longer wavelengths may be of use for some applications where the higher absorption of the materials to be processed is an advantage.

REFERENCES:
1. Y. Jeong, J. K. Sahu, D. B. S. Soh, C. A. Codemard, and J. Nilsson, "High-power tunable single-frequency single-mode erbium:ytterbium codoped large-core fiber master-oscillator power amplifier source," Opt. Lett. 30, 2997 (2005).

2. G. Frith, D.G. Lancaster and S.D. Jackson," 85W Tm3+-doped silica fiber laser," Electron. Lett. 41, 687 (2005).

3. G. P. Agrawal, Nonlinear Fiber Optics, Third Edition, San Diego, CA: Academic Press, 2001.

KEYWORDS: Laser; fiber, high power, eyesafe, directed energy.

** TOPIC AUTHOR (TPOC) **

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