Coherence-based transverse measurement of synchrotron x-ray radiation from relativistic laser-plasma interaction and laser-accelerated electrons

We observe Fresnel edge diffraction of the x-ray beam generated by the relativistic interaction of a high-intensity laser pulse with He gas. The observed diffraction at center energy 4.5 keV agrees with Gaussian incoherent source profile of full-width-half-maximum (FWHM)< 8 mu m. Analysis indicates this corresponds to an upper limit on the transverse profile of laser-accelerated electrons within the plasma in agreement with three-dimensional, particle-in-cell results (FWHM=4 mu m).