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 1.0x1012 photons/(pulsexsrxline). The source diameter is ∼20 μm (full width at half maximum) and the spatial stability is better than ±2 μm. Within an area with uniformity of 20%, the average source brightness is 4x108 photons/(pulsexsrxμm2xline), which allows operation of a compact soft x-ray transmission microscope with exposure times of a few minutes