Characterisation of a laser plasma betatron source for high resolution x-ray imaging

We report on the characterisation of an x-ray source, generated by a laser-driven plasma wakefield accelerator. The spectrum of the optimised source was consistent with an on-axis synchrotron spectrum with a critical energy of $13.8^{+2.2}_{-1.9}$ keV and the number of photons per pulse generated above 1 keV was calculated to be $6^{+1.2}_{-0.9} \times 10^{\, 9}$. The x-ray beam was used to image a resolution grid placed 37 cm from the source, which gave a measured spatial resolution of 4 µm ×  5 µm. The inferred emission region had a radius and length of 0.5 ± 0.2 µm and 3.2 ± 0.9 mm respectively. It was also observed that laser damage to the exit aperture of the gas cell led to a reduction in the accelerated electron beam charge and a corresponding reduction in x-ray flux due to the change in the plasma density profile.