Comparison of DPSSL and ArF for direct-drive laser fusion energy

The nonlinear index of refraction of a DPSSL places severe restrictions on its use with direct-drive laser fusion targets. The sub-nsec pulse needed for shock ignition reduces the DPSSL efficiency to unacceptable levels. Zooming with two or more shorter pulse lengths also reduces laser efficiency. A broad continuous laser spectrum of 10 THz, needed for all types of direct-drive targets, cannot be amplified to high powers because of the nonlinear index of refraction. Using instead a discrete set of narrow-band pulses produces a long coherence time that is not consistent with optical beam smoothing. By contrast, an ArF gas laser does not have a significant nonlinear index of refraction, and has the advantages of a shorter wavelength, 1/5 versus 1/3 micron. A short shock-ignition pulse appears to be consistent with ArF, but that will need further study. Multiple zoomings are easy. A 10 THz continuous bandwidth has been demonstrated. ISI beam smoothing is superior. A 1.0 MJ ArF laser fusion power plant might utilize 4,000 laser beams, each with 250 J. With multiplexing it would require just forty large 25 kJ ArF final amplifiers. A 1.0 MJ DPSSL with the same 250 J per beam would require one hundred times as many final amplifiers.