N132-106 TITLE: High-Power 3 Micron Fiber Based Laser System

TECHNOLOGY AREAS: Air Platform, Sensors

ACQUISITION PROGRAM: JSF-MS

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: Develop a fiber based laser system operating at room temperature at 3.0 micron that emits high average and peak powers.

DESCRIPTION: A power-scalable, compact mid-IR fiber laser platform at approximately 3 micron spectral ranges for various Naval tactical applications is needed. The 3 micron optical wavelength is a very interesting and crucial wavelength because the optical absorption coefficient of water peaks at 3 micron and is 10,000 times stronger than absorption peaks at the near-infrared 1micron wavelength. Therefore, optical efficiency of using a 3 micron laser to impart optical energy into water is up to four orders of magnitude more efficient than those at the near-infrared wavelength range where conventional solid-state and fiber laser technologies are much more mature and the lasers are much more readily available commercially.

While the coherent light sources at or near 3 micron spectral range have tremendous potential for various DoD applications, the availability of reliable, high-power fiber-based laser sources in this wavelength range of interest is very limited. Recently, Erbium doped Fluoride fiber lasers incorporating low and high reflectivity Bragg gratings have been demonstrated with continuous wave (CW) lasing over 5 Watts (W) [1] and 14 W [2] at 2.94 micron, respectively. Although these results show promise for the coherent emissions in the 3 micron wavelength range the average power is still below that of conventional bulk Erbium-doped solid state laser systems. However, these solid-state systems are still rather complex and as such require complex pump and cooling schemes to maintain beam quality and system efficiency.

The payoff in terms of size, weight and performance (SWaP) would be substantial if able to exploit the paradigm of combining the unique Erbium doping properties of solid state systems and the recent advances, ruggedness and compactness of fiber-based lasers or amplifiers based on single crystal fibers (SCFs) [3]. Recently, Sangla et. al. [4] has shown laser emission from Yb-doped Yttrium Aluminum Garnet (Yb:YAG) SCF with a micro-pulling technique. These results showed decent beam quality with lasing at 1031 nanometers (nm) and more than 2 Watts of continuous wave (CW) power. Zaouter [5] also showed direct amplification of ultra-short pulses using Yb:YAG SCF with a gain of 30 in a double pass configuration. It is expected that similar results can be achieved using Er-doped (Er:YAG) SCF. In this case, the SCF structure can serve as an amplifier for a semiconductor seed source or as an oscillator using properly designed high reflectivity and low reflectivity gratings or mirrors. Therefore, the main objective of this topic is to investigate and demonstrate the feasibility of using novel diode-pumped Er-doped fiber for generation of high-power output at approximately 3 micron with near diffraction-limited beam quality or M2. It is desired to develop a compact and robust fiber laser system for 3 micron emission wavelength, operating at room temperature, and capable of producing at least 10 W in CW mode with beam quality of M2 < 1.3. The design should be further refined to increase the CW output power level to greater than 100 Watts with beam quality M2<1.3.

PHASE I: Determine and demonstrate the feasibility of designing a compact and robust fiber laser system with the parameters requested in the description. Further refine the concept by determining the feasibility of increasing the CW as also requested in the description and provide a well-thought out (and realistic) development plan that clearly describes the power scaling architecture output power level to greater than 100 Watts. Provide a well-thought out (and realistic) development plan that clearly describes the power scaling architecture of which the power and beam quality must be at least 100 watts in CW mode and M2<1.3, respectively.

PHASE II: Design, develop and demonstrate a prototype of the fiber laser system. Assess the manufacturing yield and product reliability of the fiber laser system. Based on the experience and lessons learned provide a revised well-thought out (and realistic) development plan that clearly lays out the power scaling architecture for such a system for output with 100 W at CW mode and M2 < 1.3.

PHASE III: Fully develop and transition the high-performance semiconductor laser system and/or power-scaled architecture for maritime sensing, naval aviation LIDAR, and advanced chemical sensor applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The commercial sector can significantly benefit from this technology development in the areas of detection of toxic industrial gases, environmental monitoring, and non-invasive medical health monitoring and sensing.

REFERENCES:
1. Faucher, D., Bernier, M., Caron, N. & Vallee, R. (2009). Erbium-doped all-fiber laser at 2.94 �m. Opt. Lett., 34(21) 3313-3315.

2. Faucher, D., Bernier, M., Androz, G., Caron, N. & Vallée,, R. (2010). 20 W passively cooled single-mode all-fiber laser at 2.8 ��m. Optics Lett. 36, 1104.

3. Sangla, D., Aubry, N., Didierjean, J., Perrodin, D., Balembois, F., Lebbou, K., Brenier, A., Georges, P., Fourmigue, J., & Tillement, O. (2008). First Demonstration of Laser Emission from an Yb:YAG Single Crystal Fiber Grown by the Micro-Pulling Down Technique. in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America), paper CThFF4.

4. Nubling, R. & Harrington J. (1998). Single-crystal LHPG sapphire fibers for Er:YAG laser power delivery. Applied Optics, 37, 4777-4781.

5. Nubling, R. & Harrington J. (1997). Optical properties of single-crystal sapphire fibers. Applied Optics 36, 5934-5940

KEYWORDS: 3 Micron, Fiber Laser, Fiber Amplifier, Sensor, Solid-State Laser, Erbium

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