Debris elimination in a droplet‐target laser‐plasma soft x‐ray source

A tabletop high‐brightness line‐emitting laser‐plasma soft x‐ray source utilizing single microscopic droplets as target is shown to produce several orders of magnitude less debris than conventional‐target sources. Quantitative measurements of debris deposition rates and x‐ray flux at different directions around the droplet plasma are presented. With ethanol droplets and a 10 Hz, 70 mJ/pulse laser, typically ∼1×1012 photons/(sr⋅pulse⋅line) are emitted from the C V and C VI lines in the water window. The debris deposition is further reduced with a small, localized gas jet shield, which is transparent to the x‐rays. The deposition rate through the gas shield has been determined to be ∼0.2 pg/(sr⋅pulse). Thus, this droplet‐target laser‐plasma x‐ray source is four orders‐of‐magnitude cleaner than a low‐debris plastic tape target laser plasma of similar brightness, making it useful for x‐ray microscopy and lithography.

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