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High power parallel fiber arrays for the amplification of high peak power pulses are described. Fiber arrays based on individual fiber amplifiers as well as fiber arrays based on multi-core fibers can be implemented. The optical phase between the individual fiber amplifier elements of the fiber arra

High power parallel fiber arrays for the amplification of high peak power pulses are described. Fiber arrays based on individual fiber amplifiers as well as fiber arrays based on multi-core fibers can be implemented. The optical phase between the individual fiber amplifier elements of the fiber array is measured and controlled using a variety of phase detection and compensation techniques. High power fiber array amplifiers can be used for EUV and X-ray generation as well as pumping of parametric amplifiers.

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1. A high peak power fiber amplifier system, comprising: an array of fiber amplifiers implemented in the form of a multi-core fiber, said fiber amplifiers being spaced such that thermal fluctuations of said fiber amplifiers are matched sufficiently to limit relative phase fluctuations at fiber ampli

1. A high peak power fiber amplifier system, comprising: an array of fiber amplifiers implemented in the form of a multi-core fiber, said fiber amplifiers being spaced such that thermal fluctuations of said fiber amplifiers are matched sufficiently to limit relative phase fluctuations at fiber amplifier outputs to a bandwidth less than 10 kHz, and such that optical energy coupling between any of the fiber amplifiers of said array of fiber amplifiers is negligible;a laser source for seeding said array of fiber amplifiers;a beam distributor disposed between said laser source and said array of fiber amplifiers to distribute a pulse from said laser source into a plurality of beam paths incident on corresponding amplifiers of the array, wherein beams in said path have a spatial distribution substantially similar to the spatial distribution of an output of said laser source;at least one pump source configured for optically pumping said array of fiber amplifiers;a plurality of phase-control elements arranged in a spatial relation and optically connected to fiber amplifiers of said array of fiber amplifiers, said elements modifying an optical phase of at least one fiber amplifier output in response to phase-control signals;a phase control unit for producing said control signals to control the optical phase at the output of a majority of said fiber amplifiers of said array of fiber amplifiers, wherein said control signal and said phase control elements stabilize the optical output phase between the majority of said fiber amplifiers of said array of fiber amplifiers; andan optical combiner which receives phase stabilized pulses from said fiber amplifiers and optically combines said phase stabilized pulses to form a near diffraction limited output beam and a high peak power optical pulse at an output thereof. 2. The high peak power fiber amplifier system according to claim 1, said system comprising a phase plate inserted downstream of the output of said array of fiber amplifiers, so as to maximize the Strehl ratio of the output of said array of fiber amplifiers. 3. The high peak power fiber amplifier system according to claim 1, wherein energy coupling between amplifiers of said array of fiber amplifiers is less than 1%. 4. The high peak power fiber amplifier system according to claim 1, wherein said relative phase fluctuations are less than 1 KHz. 5. The high peak power fiber amplifier system according to claim 1, wherein said phase control unit comprises a detector array and an adaptive algorithm for processing phase information obtained from said detector. 6. The high peak power fiber amplifier system of claim 5, wherein said adaptive algorithm comprises a genetic algorithm. 7. The high peak power fiber amplifier system according to claim 1, wherein said laser source comprises a mode locked laser. 8. The high peak power fiber amplifier system according to claim 7, wherein said laser source comprises a pulse stretcher for increasing a pulse width of a pulse emitted from said mode locked laser. 9. The high peak power fiber amplifier system according to claim 1, wherein said multi-core fiber comprises a leakage channel fiber. 10. The high peak power fiber amplifier system according to claim 9, wherein said leakage channel fiber is a polarization maintaining fiber. 11. The high peak power fiber amplifier system according to claim 1, said system comprising a signal reference arm and a phase compensator, said reference arm being arranged to interfere with a fraction of a beam passing backward through said array of fiber amplifiers so as to provide compensation of the optical phase of each individual fiber amplifier of said array of fiber amplifiers for a beam passing forward through said array of fiber amplifiers with said phase compensator. 12. The high peak power fiber amplifier system according to claim 11, wherein said phase compensator comprises a spatial light modulator. 13. The high peak power fiber amplifier system according to claim 1, wherein energy coupling between fiber amplifiers of said array of fiber amplifiers is less than 0.1%. 14. The high peak power fiber amplifier system according to claim 1, wherein said array of fiber amplifiers is configured in a system for EUV or X-ray generation. 15. The high peak power fiber amplifier system according to claim 14, wherein said system for EUV or X-ray generation is used as a light source in optical lithography. 16. The high peak power fiber amplifier system according to claim 1, wherein said array of fiber amplifiers is configured as a pump source for parametric amplification. 17. The high peak power fiber amplifier system according to claim 1, wherein said fiber amplifiers comprise individual fibers constructed from step-index fiber, photonic crystal fiber or Bragg fibers. 18. The high peak power fiber amplifier system according to claim 1, further comprising side-pumping elements for the amplifier arrays. 19. The high peak power fiber amplifier system according to claim 1, wherein the amplifier is constructed in a double pass configuration. 20. The high peak power fiber amplifier system according to claim 1, wherein a phase-control element comprises a portion of a segmented mirror array. 21. The high peak power fiber amplifier system according to claim 1, wherein a phase-control element comprises a portion of a MEMs array. 22. The high peak power fiber amplifier system according to claim 1, wherein said laser source for seeding said array produces pulses having pulse widths in femtosecond range or in the range from 1 picosecond to one microsecond. 23. The high peak power amplifier system according to claim 1, wherein said output pulses comprise a pulse width in the range from about 100 fs to 1 ns. 24. The high peak power amplifier system according to claim 1, wherein said output pulses comprise a pulse width in the range from about 100 ps to 50 ns. 25. The high peak power fiber amplifier system of claim 1, wherein said array of fiber amplifiers are disposed about a common center and approximately equidistant from said center. 26. The high peak power fiber amplifier system of claim 1, wherein said array of fiber amplifiers is disposed in a single ring and approximately equidistant from a common center. 27. The high peak power fiber amplifier system of claim 1, wherein said phase control elements form a portion of an integrated phase modulator. 28. The high peak power fiber amplifier system of claim 1, wherein nearly diffraction limited outputs are obtainable for pulse widths greater than about 10 fs as a result of phase stabilization.