To Investigate and Develop a Reduced Cost Completely Monolithic High Energy Ultrafast Fiber Amplifier Based on Microstructured Fiber and Counter Pumping

A very diverse set of applications from lasers for accelerator applications to defense, to industrial to scientific and biomedical applications need to achieve ultrafast laser beams that have both high energy per pulse and high average power. In current lasers systems only one or the other is achievable. Networks of coherently combined massively parallel arrays of fiber lasers provide the promise of achieving both high pulse energy and high average power. The primary obstacle in the way of fulfilling this promise is the current high cost of these individual ultrafast fiber laser channels. Increasing the available energy per pulse in each channel will produce geometric reductions in cost. The goal of this effort has been to develop methods for increasing pulse energy while either maintaining or reducing the manufacturing cost of each channel. In the Phase I portion of this program, 3 different non volume related cost reduction methods have been demonstrated. The first is the use of microstructured fiber such as Photonic Crystal Fibers (PCF) which have a factor of 4 cross sectional area increase over conventional Large Mode Area (LMA) Step Index Fibers (SMA). This translates in to a greater that factor of 4 decrease in system cost as only one channel would be needed instead of 4 for the same pulse energy. The second is the demonstration of completely monolithic fiber amplifier structures. Monolithic structures have no free space fiber coupling so no mechanical mounts, no stable and heavy optical breadboards, and no opportunities for misalignment and contaminations, greatly reducing assembly costs and increasing reliability and ruggedness. Finally during the program a counter pumped monolithic harness was developed, fabricated and tested with a chirped pulse seed source and a factor of 3 increase in achievable energy was observed. Overall, a greater than order of magnitude reduction in cost has been demonstrated. The proposed Phase II program will achieve an additional order of magnitude reduction in per channel cost through the use of composite amplifier structures where over 60% of the expensive microstructured fiber will be replaced with less expensive LMA SIF fiber where the peak powers are low. Even higher energies will be achieved through the use of very short sections of PCF rod amplifiers. For these amplifiers, specific, low loss double mode adapters will need to be developed. In addition means for packing multiple channels very close to each other with a method that allows for serviceability for each channel will also be developed. The Phase II program will culminate with the fabrication and testing of a 7 channel parallel ultrafast system. Scientific, Industrial and Biomedical applications will benefit greatly by having access to the devices being developed here allowing ultrafast lasers to move into more parts of our lives. Ultrafast Fiber Lasers are at the forefront to opening a whole new era in laser applications from medicine to industrial to defense applications. This program will increase the available power from these lasers by orders of magnitude while making them low cost and highly reliable pushing ultrafast lasers deeper to solve societies needs.