N121-059 TITLE: High Power Ultra-Short Pulse Bulk Laser Amplifier at Eye Safer Wavelengths

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 is to develop a robust, high power (10�s of mJs), kHz repetition rate ultra-short pulse (~100fs) laser amplifier at eye safer wavelengths within the 1.5um � 1.8um atmospheric transmission window.

DESCRIPTION: Numerous physical processes that are useful for defense and commercial applications have been demonstrated using energetic (~100 mJ) ultra-short pulse (USP) lasers. Laser systems demonstrating these processes can create Terawatt peak powers and very broadband emissions, typically using Ti:Sapphire gain media and Master Oscillator Power Amplifier Chirped Pulse Amplification (MOPA CPA) architectures (see references 1, 2, and 3). Thermal issues, however, typically limit the power amplifier repetition rates for such systems (see reference 4), and 800nm wavelengths generated using Ti:Sapphire crystals are not considered eye safe. Other gain media have shown great promise for scaling to high average power for kHz-class repetition rates, such as Yb-doped thin disks (see reference 5) and cryogenically cooled laser systems (see reference 6), but these systems operate at 1 um and are not eye-safe. Furthermore, the bandwidth for these systems is still limited in crystals suitable for high power. There is a need to develop a high power ultra-short pulse gain material and laser architecture for the atmospheric transmission window between 1.5um and 1.8 um. The issue being addressed by going to these wavelengths is one of collateral damage and ready acceptance of these as items of use in the military, for at these wavelengths accidental eye damage is far less likely than at shorter wavelengths. Furthermore, pulse lengths of ~ 100fs should be obtained. A scaling path to achieve pulse energies on the order of 100mJ is required. An initial repetition rate of 100�s of Hz and a clear path for repetition rates exceeding 1 kHz or greater are also desired. Several companies have commercialized ultra-short pulse fiber oscillators that operate at 1.55 microns. It is envisioned that the proposed solutions may include a previously developed oscillator followed by a high power bulk laser amplifier in a MOPA configuration to achieve the desired pulse energies.

PHASE I: Develop an innovative concept for a laser amplifier and demonstrate the feasibility of the concept through either laboratory experiments and physical measurements or citing existing proof-of-principle laboratory physical measurements. Demonstrate the feasibility of scaling the concept to a 100 mJ, 1 kHz, 100fs laser system at an eye safer wavelength. Provide a Phase II development plan that includes performance goals and key technical milestones.

PHASE II: Based on the results of Phase I and the Phase II development plan, an ultra-short pulse laser system will be built and used to demonstrate 100fs pulses of more than 50mJ at an eye safer wavelength within the 1.5 um transmission window. This can be done either single pulse or at low repetition rates. A conceptual design will be developed, based on the demonstration, for a laser system which would operate at repetition rates in excess of 1 kHz, pulse times of the order of 100fs, and pulse energies exceeding 100mJ. The scaling path for achieving this system will be detailed.

PHASE III: If Phase II is successful, the contractor is expected to support the Navy in further development of the laser amplifier should a Phase III contract be awarded. The focus of Phase III would be a full scale prototype demonstration to support transition of the amplifier to Navy use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: There is a substantial market of ultrafast laser vendors who could seek to enhance their core technology by making use of next generation laser amplifiers. Ultrafast lasers can be utilized in a variety of commercial applications, including surgical, manufacturing, and laser processing.

REFERENCES:
1. Wille, et. al., "Teramobile: A Mobile femtosecond-terawatt laser and detection system", Eur. Phys J. AP 20, pp183-190 (2002);

2. Rohwetter, et. al. "Filament induced remote surface ablation for long range laser-induced breakdown spectroscopy operation", Spectrochmica Acta Part B 60 pp 1025-1033 (2005);

3. S.L. Chin, "Propagation of powerful femtosecond laser pulses in optical media: physics, applications, and new challenges:, Can J. Phys 86 pp 863-905 (2006).

4. Gaudiosi, et. al., "Multi-kilohertz repetition rate Ti:Sapphire amplifier based on down-chirp pulse amplification", Opt. Exp. 14(20), (2006) 99277; Backus, et.al. "High power ultrafast lasers", Rev. Sci. Inst. 69(3) pp 1207-1223 (1998)

5 Metzger, et. al., "High-repetition-rate picosecond pump laser based on Yb:YAG disk amplifier for optical parametric amplification", Opt. Lett 34(`4) pp. 2123-2125 (2009)

6. Rand, et. al., "Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG", Opt. Lett. 36(3) pp. 340-342 (2011).

KEYWORDS: Laser amplifier; high power laser; high energy laser; laser; ultra-short pulse laser; directed energy

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