Novel high peak- and average-power ultrafast using parametric beam combination of fiber lasers

Ultrafast lasers have moved from laboratory instruments only available in a few laboratories worldwide to ubiquitous tools both in research laboratory and in industry. In particular, ultrafast lasers have become the cornerstone to drive secondary sources of coherent X-rays and ultrafast electrons. These secondary sources – in particular coherent X-rays – find applications as crucial as the inspection of photolithography masks in the semi-conductor industry. In this project, we propose to develop a reliable method to combine multiple high-power lasers, providing a pathway toward ultrashort, high-energy and high average power lasers. A prerequisite to widely deploy ultrafast lasers in industrial settings is to reliably scale the average power and pulse energy of these systems, a challenging task that has so far eluded the laser development community. In this work, we have started to tackle this problem. The community has identified that the path to scale ultrafast lasers to high energy and average power is via multiplexing and combining of multiple amplifiers. The combination techniques that have been employed to date put stringent requirements on each of the high-power amplifier to be combined, making beam combination exponentially challenging as the number of amplifiers increases. In this project, we propose to use parametric chirped pulse amplification of multiple pump beams and a single signal beam, enabling the combination of multiple energy/average power limited amplifiers into a single beam. In Phase I, we demonstrated and numerically simulated the combination of two 1 m wavelength beams into a single 1.5 m wavelength beam with > 100 J of energy and a spectrum supporting < 100 fs pulses. The experiment was performed at 1 kHz. In parallel, we investigated the development of high average power fiber amplifiers to the few tens of Watt level. The aim of this part of the work was to determine suitable parameters, engineering choices and architecture to later develop an all integrated, parallelized set of rod-type fiber amplifiers that would individually operate in the average power and energy limited regime and be combined into a single beam via optical parametric beam combination. These investigations have allowed us to develop a blueprint for a multi-channel amplifier and allowed us to establish contact with relevant manufacturers in the field for future collaborations. In Phase II, we therefore propose to (i) develop a two-color front-end system that will deliver ~30 W average power at repetition rate ≤1 MHz at 1 m wavelength and nJ, 100 MHz, 1.5 m wavelength pulses with a spectrum supporting < 100 fs pulses; (ii) scale the 1 m pulses from the front-end from the 30 W level to the 400 W level in a set of 4-parallel rod-type fiber amplifiers; (iii) perform R&D to optimize the parametric combination efficiency and reliability and (iv) demonstrate combination of the four, hundred W level channels into a single 1.5 m wavelength beam via parametric beam combination. This system will be used to develop a commercial secondary source of coherent soft X-ray making it the first, commercially available, high flux, half-keV coherent photon source.