Advances in High Average Power, 100 Hz Repetition Rate Table-Top Soft X-Ray Lasers

Abstract

We discuss new results of the demonstration of 100 Hz table-top soft x-ray lasers operating at wavelengths from 10.9 nm to 18.9 nm and report the highest soft x-ray laser average power to date at sub-20 nm wavelength. The results include the generation of average powers up to 0.2 mW at λ = 18.9 nm, 0.1 mW at λ = 13.9 nm, and 20 μW at λ = 11.9 nm. These lasers are driven by a compact chirped pulse amplification laser system featuring diode-pumped, cryogenically-cooled Yb:YAG power amplifiers that produces 1 J pulses of 5 ps FWHM duration at 100 Hz repetition rate. The driver laser pulse shape was tailored to more efficiently pump soft x-ray plasma amplifiers operating at sub-15 nm wavelengths leading to a threefold increase in the λ = 13.9 nm laser pulse energy and lasing down to 10.9 nm. The pump pulse profile consisting of a nanosecond ramp followed by two closely spaced peaks of picosecond duration, is shown to create a plasma with an increased density of Ni-like lasing ions at the time of peak temperature, resulting in a larger gain coefficient over a temporally and spatially enlarged space. The development of rotating solid targets with high shot capacity has allowed the uninterrupted operation of the λ = 18.9 nm soft x-ray laser for hundreds of thousands of consecutive shots making it suitable for applications in nanoscience and nanotechnology that require high photon flux at short wavelengths. As a proof-of-principle demonstration of the utility of this laser in such applications we have lithographically printed an array of nanometer-scale features through coherent Talbot self imaging. These results open the path to milliwatt average power table-top soft x-ray lasers.