N112-130 TITLE: Pulse Compressor for Long Stretch Factor in High-Energy Ultrafast Fiber Lasers at Eye-Safer Wavelengths

TECHNOLOGY AREAS: Electronics

ACQUISITION PROGRAM: PMS 405, Directed Energy & Electric Weapon Systems Program Office, ACAT N/A

OBJECTIVE: Develop and demonstrate a low loss ultrafast laser pulse compressor capable of compressing greater than (>)3 ns stretched pulses down to less than (<)500 fs in high energy (>1 mJ) fiber-optic chirped pulse amplification (CPA) systems at eye-safer wavelengths.

DESCRIPTION: Ultrafast lasers offer a variety of potential applications of interest to the Navy in the fields of sensing, diagnostics and distance interrogation as well as with weapons potential. At the pulse energy and average power levels of interest, current state-of-the-art pulse compressors are limited in compression factor due to physical size constraints, alignment sensitivities, and/or high optical losses. These limitations impede the scaling of fiber-optic CPA system pulse energy and greatly restrict the deployment of practical ultrafast lasers.

Due to their compactness, suitability for direct diode laser pumping, high efficiency and scalability, the Navy is interested in the development of high peak and average power, high-energy fiber-based CPA systems at eye-safer wavelengths. High-energy lasers at eye-safer wavelengths present much lower ocular hazards to the military personnel than lasers emitting at other wavelengths. Such systems would enable numerous applications and allow for easier integration into existing sea and air based platforms.

Scaling the pulse energy from chirped-pulse fiber amplifiers to the millijoule level at high average power has been limited by the nonlinear effects in fiber that are detrimental to the amplified pulse quality. Self-phase modulation and other nonlinearities limit the minimum pulse durations achievable by pulse compression following the amplification stage. A primary technique for postponing these issues is to increase the linear pulse temporal stretch factor from <1 ns to 3 ns or greater. The proportional decrease in pulse peak irradiance for a given pulse energy enables a likewise proportional increase in the achievable amplified pulse energy for the system. Compressing >3 ns pulses to <500 fs using the incumbent Treacy geometry is not feasible in a compact, deployable package owing to the required diffraction grating size, the long optical path length, and the high losses imposed by conventional multi-pass schemes.

The compressor must have compact size (<1000 cm3 volume), high efficiency (>75% transmission), no degradation of spatial mode quality, and dispersion properties compatible with fiber-optic pulse stretchers used in CPA systems. The compressor must operate at high laser pulse energy (>>1 mJ) and high average power (>25 W) without distortion to the laser or damage to the compressor elements. The compressor must be demonstrated in an end-to-end ultrafast fiber laser system at eye-safer wavelengths with pulse output: >1 mJ energy, <500 fs temporal full width at half maximum (FWHM), and negligible pulse pedestal (>95% integrated energy within the 10 ps centroid).

PHASE I: Conduct research, design, and analysis on the pulse compressor architecture that enables long stretch factor (>3 ns), high efficiency (>75% transmission), and high energy (>1 mJ) in a compact, robust form factor. Prove feasibility of device fabrication based on design architecture and materials evaluation. The Phase I effort should include modeling and simulation results supporting pulse compression performance claims. The effort should also produce a draft testing methodology that can be used to demonstrate performance of the end-to-end fiber-based CPA system proposed for the Phase II effort.

PHASE II: Develop a prototype long stretch factor (>3 ns) pulse compressor based on the technology advances and methods identified in Phase I. Demonstrate the required optical performance in an end-to-end fiber-based CPA system with output energy >1 mJ, pulse width <500 fs, and eye-safer center wavelength, e.g. 1.55 �m.

PHASE III: Develop a long stretch factor pulse compressor capable of mass production for a variety of civilian and military uses. The final system may be expected to be "hardened" for field use, depending on mission needs.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Long stretch factor pulse compressors enable higher pulse energy and average power for ultrafast lasers in smaller footprints. There is a substantial market of ultrafast laser vendors who could seek to enhance their core technology by making use of next generation fiber amplifiers. Ultrafast lasers can be utilized in a variety of commercial applications, including surgical, manufacturing, and laser processing.

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

2. Ultrafast Lasers: Technology and Applications Edited by: Martin Fermann, Almantas Galvanauskas, and Gregg Sucha New York, Marcel Dekker, Inc. 2003.

3. Tino Eidam, Stefan Hanf, Enrico Seise, Thomas V. Andersen, Thomas Gabler, Christian Wirth, Thomas Schreiber, Jens Limpert, and Andreas Tünnermann, "Femtosecond fiber CPA system emitting 830 W average power," Optics Letters 35, pp.94-96 (2010).

KEYWORDS: Ultrafast Lasers; Chirped Pulse Amplification; High-energy fiber amplification; High peak power pulses; Compact ultrafast fiber amplifiers; Eye-safer fiber amplifiers

** TOPIC AUTHOR (TPOC) **

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