N102-150 TITLE: Broad Band Fiber Lasers (Wavelength of ~500nm to 1800nm)

TECHNOLOGY AREAS: Sensors, Weapons

ACQUISITION PROGRAM: Laser Weapon System/Close In Weapon System

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: Perform the required R&D in support of design trade studies to determine best approach to develop a laboratory prototype laser that can produce laser light with a wavelength between approximately 500 nm to 1800 nm either as an instantaneous bandwidth, or continuously sweep wavelength over the desired bandwidth with the sweep time less than 1 millisecond. Meeting the R&D challenges will result in laser output beam quality that should be better than 3X the diffraction limit, be continuous wave (CW) or pulsed with the pulse repetition rate better than 1000 Hz, and an average power of greater than 50 watts. The laser should be able to run continuously for more than 10 minutes with no loss of average power or beam quality. A successful design will lead to improved potential for broadband communications and increased opportunities for electro-optic jamming. The military transition is envisioned to be integrated into LaWS (Laser Weapon System).

DESCRIPTION: The purpose of this topic is to develop a broadband (500 nm � 1800 nm) laser source based on existing technology or through R&D achieved improvements to current laser technology which enables the end user to project broadband laser energy either CW or pulsed with relatively high repetition rates of 1000 Hz minimum. The contractor shall perform the R&D so that the system may employ nonlinear devices or novel technologies which achieve the stated requirements and allow for control of output beam quality and divergence. The results of this work effort will enable solutions for applications of interest to the U.S. Navy, including, but not limited to, directed energy (DE) weapons, countermeasures to electro-optic (EO) systems, target illumination with a frequency agile source, and atmospheric transmission studies in situ.

Nonlinear devices such as optical parametric oscillators (OPO�s) have provided tunable output when pumped by an appropriate laser source however, they are generally limited in bandwidth by properties associated with the nonlinear material such as absorption and/or reduced nonlinear coefficients as one tunes away from the degenerate point. Fiber lasers offer opportunities for broadband output via various doping elements and amplification through multiple stages of optical gain systems. Currently R&D programs involving new dopant schemes and various glass media have created lasers which provide more options for visible to near infrared output than previously realized by former solid state laser designs. Some of the remaining R&D challenges involving higher power fiber lasers stem from parasitic loss mechanisms such as Brillouin and Raman scattering which require changes in fiber design necessary to suppress such loss mechanisms.

Improved wall plug efficiency for future shipboard laser systems will be critical with respect to power management and the reduction of strain on existing ship based power resources. Thermal management as well as the ability to yield a relatively stable and compact laser system is also important for integration of hardware onto existing and newer ship designs. Mitigation of environmental impact as a result of operating in a maritime environment is important towards increasing mean time between failure for total system operation as well as key components in the device design.

PHASE I: The contractor would most likely conduct supporting research and analysis of possible system approaches towards development of a broadband laser source with wavelength output between 500 nm � 1800 nm. The work should establish plausible and realizable technological solutions achievable within a two year time frame for subsequent design, development and testing of a working device. Cost analysis as well as material development should be included in the study so as to ascertain critical needs not yet fully developed or readily available given current technology. The design should illustrate strong potential towards meeting or exceeding the program objectives.

PHASE II: Based on a successful Phase I development, complete the required R&D identified in support of the development. An experimental prototype device should be designed end to end and sub components machined and assembled in concert with demonstrated performance objectives. A finished prototype should be tested for compliance to all objectives with repeatable results and established mean time between failure data on the system prototype and subcomponents. Data packages on all critical subcomponents will be provided throughout the development cycle and test results will be provided for regular review of progress. It is expected that a working prototype will be capable of demonstrating 85% or more of the expected bandwidth as well as stated power levels of 50 watts for 90% of the device bandwidth in addition to the operational capability of 10 minutes continuous without degradation to device or device performance.

PHASE III: The prototype laser system developed in Phase II will be ruggedized for testing in a maritime environment. This device will also be fine tuned and engineered for deployment in both civilian and military applications. The testing requirements will be specific to each application and will be created in concert with available resources and platforms where testing is anticipated.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This device has strong potential uses in the private and University sectors where chemical and physical property analysis of materials is currently performed by spectroscopic processes employing broadband tunable sources. Furthermore, the medical device development community may find this device applicable towards their interest in development of non-invasive methods for determining fluid chemistry in both research and direct medical applications.

REFERENCES:
1. P.F. Wysocki, M.J.F. Digonnet, and B.Y. Kim, "Broad-spectrum, wavelength-swept, erbium-doped fiber laser at 1.55 �m", Optics Letters, Aug. 15, 1990 vol. 15, No. 16, pp. 879-881

2. M. J. F. Digonnet, Rare Earth Doped Fiber Lasers and Amplifiers, 2nd edition., CRC Press, Boca Raton, FL (2001)

3. A. Galvanauskas, "Mode-scalable fiber-based chirped pulse amplification systems", IEEE J. Sel. Top. Quantum Electron. 7, 504 (2001)

4. R. G. Smith, "Optical power handling capacity of low loss optical fibers as determined by stimulated Raman and Brillouin scattering", Appl. Opt (11), 289 (1972)

5. V. I. Kovaloev and R. G. Harrison, "Suppression of stimulated Brillouin scattering in high-power single-frequency fiber amplifiers", Opt. Lett. 31 (2), 161 (2006)

KEYWORDS: Optical parametric oscillator, fiber laser, Brillouin scattering, Raman scattering, nonlinear, directed energy, Laser Weapon System (LaWS)

** TOPIC AUTHOR (TPOC) **

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