HELDP applications require lasers to create both high energy pulses and these pulses at high repetition rates for high average powers. While bulk solid-state lasers can provide the required high pulse energies, thermal effects limit their use to <10Hz. Fiber lasers, on the other hand, can provide average power levels to the multi kW level yet are limited in pulse energy due to the onset of fiber nonlinearities. There is recently great interest in coherently combined fiber laser arrays where a single seed source is split many ways and directed into a parallel array of fiber amplifiers and then coherently combined into the far field either in a tiled configuration, a mirror structure or a diffractive optical element. Even lower power HELDP applications, however, would require hundreds, even thousands of individual fiber lasers. Current fiber laser arrays are very complex, requiring individual pump lasers, combiners and mode adapters for each channel. Creating useful and cost-effective fiber laser arrays requires developing technologies that make parallel many of these fiber laser components. Optical Engines proposes a high energy fiber laser array based on the patent pending Flys Eye Fiber Laser Array (FEFLA) concept. This technology is based on the high-power tapered end cap technology developed under DoE SBIR contract DE-SE0015905. In this proposal these tapered end caps will be constructed of a hexagonal glass fiber material appropriately sized such that all of the end caps are tightly stacked together such that the output face of the fiber laser array resembles a flys eye structure. In this way a single low cost, low alignment tolerance laser diode pump source at the multi kW level can pump the entire array, eliminating individually fiber coupled pump diodes and costly pump signal combiners, eliminating over 90% of the components of the fiber laser array. In the phase 1 program, Optical Engines, through analysis, simulation, and experimentation will develop the necessary glass processing technologies to demonstrate a single channel and 3 channel FEFLA structure and will fully characterize pumping efficiency and signal output integrity. These include, but are not limited to, developing and optimizing the taper size and length, the taper to laser amplifier splice and the packing and mounting structure. These configurations will be tested up to 100W of pump to test for power handling capability. The FEFLA pumping structure also creates many opportunities for completely new and novel Ultrafast fiber laser array architectures in order to reduce cost and increase pulse energy and peak power, and these different approaches will be analyzed as well.
