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 domain. Rod-type photonic crystal silica fibers have been used mainly 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 of free space coupling severely restrict their use in beam combining of many ultrafast lasers. NP Photonics proposes to develop compact and robust short- length 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 Photonicsĺ highly doped phosphate fibers have already shown the unique advantage of 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, NP Photonics has designed and fabricated highly Yb-doped large-mode-area phosphate fibers for ultrashort pulse amplification. Core-pumped pencil amplifiers and 100-watt fiber amplifiers based on highly Yb-doped phosphate fibers were developed and tested. In Phase II, 1-W pencil amplifier arrays and short-length 100-watt Yb-doped fiber amplifier arrays will be developed and tested for ultrashort pulse laser beam combining. In addition to DOE applications, the proposed short-length fiber laser amplifiers can be used in many other applications, such as advanced material processing, medical applications, spectroscopy, remote sensing, and Lidar.