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DIRECTED ENERGY PROFESSIONAL SOCIETY

Abstract: 24-Symp-072

UNCLASSIFIED, PUBLIC RELEASE

High Peak and Average Power Tm:YLF Lasers

Next generation peak and average power laser systems are anticipated to drive intense laser-matter interactions at unprecedented repetition rates to ablate targets and produce high flux secondary photon and charged particle sources. To deliver this capability for a range of scientific and national security applications, laser architectures combining a unique solid-state laser gain material, compact amplifier cavity, and efficient pulsed energy extraction technique must be developed and optimized. For this purpose, LLNL’s Big Aperture Thulium (BAT) laser concept has been designed to efficiently generate high energy, femtosecond duration pulses with petawatt-class peak powers, while simultaneously operating at 300kW-class average power. The BAT laser concept employs thulium-doped yttrium lithium fluoride (Tm:YLF) as the gain material, which emits near 1900nm central wavelength and can be pumped directly with high power, continuous wave laser diodes due to the strong absorption peak near 800nm wavelength and long energy storage lifetime of 15ms. Furthermore, in Tm:YLF, a unique cross-relaxation effect can result in two seed photons generated per single pump photon, thereby substantially reducing the quantum defect loss to nearly 16%. Within the gas-cooled, multi-slab BAT laser architecture, amplification occurs under the multi-pulse extraction regime to efficiently extract high pulse energies at kHz-level repetition rates, while remaining at a safe individual pulse fluence. Using this technique, Tm:YLF-based laser systems can also be operated under burst-mode conditions with a variety of pulse shapes for substantial improvements to the size, weight, and power (SWaP).

To demonstrate the feasibility of the BAT laser concept, we have recently conducted multiple proof-of-principle experiments using a single compact, multi-pass Tm:YLF amplifier. These results include the generation of >100J pulse energies in millisecond-duration pulses, >20J in 20ns pulses, and multi-kHz burst amplification with 19% optical-to-optical efficiency. Additionally, we have demonstrated an order of magnitude higher heat extraction from Tm:YLF than any laser material currently employed in gas-cooled, multi-slab petawatt-class systems to-date, as well as chirped pulse amplification (CPA) to the joule-level and compression to sub-300fs for the first time, thereby achieving >1TW-level peak powers using this average power scalable material. To the best of our knowledge, these are the highest pulse energies and peak powers demonstrated for any laser architecture operating near 2-micron wavelength worldwide. Here, we will introduce the BAT laser concept, describe the recent experimental results, and provide an outlook on the upcoming Tm:YLF architecture developments, including the high repetition rate and burst-mode operation of the TW-level Tm:YLF CPA system.

This work was performed by LLNL under Contract DE-AC52-07NA27344, and was supported by the LLNL LDRD Program under Project Numbers 19-DR-009 and 21-ERD-016, by the DOE SC ARDAP Accelerator Stewardship Program under Project SCW1648, and by the Defense Advanced Research Projects Agency (DARPA) under the Muons for Science and Security Program.

UNCLASSIFIED, PUBLIC RELEASE