Low-nonlinearity Yb-doped Fiber Amplifier Arrays for Ultrafast Fiber Laser Combining

Beam combining of many ultrafast lasers is a very promising route to achieving high peak power and high average power laser systems required for DOE acceleration applications. Fiber lasers have become key workhorses for power scaling of ultrafast laser sources due to their high single-pass gain, outstanding heat-dissipating capability, excellent beam quality, inherent simplicity, and compactness. However, due to the long interaction length and small core size of a conventional silica fiber amplifier, there will be a large amount of accumulated nonlinearity distorting the ultrashort pulses, both in the temporal and spectral domains. Rod-type photonic crystal silica fibers have been mainly used for high-power ultrafast laser amplifiers with mitigated nonlinear effects due to their large mode field areas. However, the high cost of rod-type photonic crystal fibers and the need for free space coupling severely restrict their use in beam combining of many ultrafast lasers. NP Photonics proposes to develop compact and robust shortlength all-fiber amplifier arrays that are suitable for ultrafast fiber laser beam combining with low nonlinearity and significantly reduced cost by taking advantage of our unique highly doped phosphate fiber laser technology. NP Photonics’ highly doped phosphate fibers have already shown the unique advantage for ultrashort pulse amplification with ultra-low nonlinearity because they have absorptions ten times larger than conventional silica fibers and can be made with very large single-mode cores using our proprietary rod-in-tube technique. In the Phase I program, we will demonstrate the feasibility of the proposed 1-W pencil amplifier and 100-watt-level largemode-area fiber amplifier for ultrafast laser amplification and coherent combination. Short-length Yb-doped fiber amplifier arrays for laser beam combining will be developed and delivered to DOE laboratory for test in Phase II. Our proposed short-length fiber laser amplifiers can be used to achieve high peak and average power mode-locked and Q-switched laser sources that have found applications in many other fields such as advanced material processing, medical applications, spectroscopy, remote sensing, and Lidar.