Liquid-nitrogen-jet laser-plasma source for compact soft x-ray microscopy

We describe a liquid-nitrogen-jet laser-plasma source with sufficient brightness, uniformity, stability, and reliability to be suitable for compact water-window soft x-ray transmission microscopy. A cooled capillary nozzle arrangement allows long-term operation and avoids previously reported jet instabilities. The source is quantitatively characterized by calibrated slit-grating spectroscopy and zone-plate imaging. The absolute photon number in the major spectral lines ( λ = 2.48 nm and λ = 2.88 nm ) is 1.0 × 10 12 photons ∕ ( pulse × sr × line ) . The source diameter is ∼ 20 μ m (full width at half maximum) and the spatial stability is better than ± 2 μ m . Within an area with uniformity of 20%, the average source brightness is 4 × 10 8 photons ∕ ( pulse × sr × μ m 2 × line ) , which allows operation of a compact soft x-ray transmission microscope with exposure times of a few minutes.