Observation of enhancement in water window laser plasma X-ray under nitrogen atmosphere

X-ray microscope using water window (WW) X-rays (2.3 to 4.4 nm) is expected as one of the tools to observe living cells and biomolecules. In order to obtain their images with a higher spatial resolution, X-ray photons number has to be increased significantly. Recently, we found that the WW intensity was enormously enhanced when a gold target was irradiated with a laser pulse (1064 nm, ~7 ns, 1 J) under low-pressure N2 atmosphere. In order to clarify the mechanism of the phenomenon, emission spectroscopy was carried out under various gas species (N2, O2, Ne, He and Ar) and their pressures up to 1 kPa. For X-ray measurement, a grazing incidence spectrometer (flat field grating: 2400 grooves/mm) with a toroidal mirror was used. In addition, a pinhole camera with an aperture of 10 mm was installed to measure two dimensional X-ray images. The mechanism of the WW X-ray enhancement will be described in terms of atomic physics, especially, X-ray innershell ionization and subsequent Auger electron process.60th Annual Meeting of the APS Division of Plasma Physic