Determination of the size and structure of an X-pinch x-ray source from the diffraction pattern produced by microfabricated slits

X-pinch plasma emits subnanosecond bursts of x rays in the 3-10-keV energy range from a small source. As such, it has been used for high-resolution point-projection imaging of small, dense, rapidly changing plasmas as well as for submillimeter-thick biological samples. In addition to the effect of source size on geometric resolution, a small source size can also provide high spatial coherence of x rays, enabling the rays to be used for imaging weakly absorbing objects with excellent spatial resolution by a method called phase-contrast imaging. To determine the source size, we microfabricated gold slits and imaged them in a point-projection radiography configuration. The shape of the shadow image pattern depends on the source size and energy band of the x rays, the shape and material used for the slits, and the geometry of the experiment. Experimental results have been compared with wave-optics calculations of the expected image pattern as a function of all the parameters listed above. For example, assuming a Gaussiansource distribution, an effective source size in 2.5-4.1 A radiation (1 A = 0.1 nm) of 1.2 +/- 0.5 microm (full width at half-maximum) was determined for a 20-microm Mo wire X pinch. Characterization of the size and structure of the x-ray bursts from X pinches by the use of different wire materials and different slit structures is made.