Pinch Plasma Source for X-Ray Microscopy with Nanosecond Exposure Time

The strong demand for bright, compact, and inexpensive sources for x-ray microscopy has stimulated the development of flash x-ray sources. In this paper, the requirements for such a source are analyzed under boundary conditions given by the concept of an imaging x-ray microscope using mirror condenser and Fresnel zone plates for high-resolution imaging. It is found that the Lyman-α (1s–2p) line of hydrogen-like nitrogen (N VII) at λ = 2.48 nm emitted from a nonequilibrium plasma of about 200 eV temperature and 10²⁰ cm⁻³ electron density is best suited. These conditions are achieved in medium-current pinch-plasma devices. Using detailed numerical simulation of the physical processes of such a device, optimization criteria for the integrated spectral brightness (ISB) are found. Measurements of the ISB confirm these optimization criteria. The results show that the spectral emission characteristics of an optimized pinch plasma souce are compatible with the demands of the mentioned x-ray microscopy concept. These emission characteristics are compared with laser-produced plasma sources. Using the optimized source with an ISB exceeding 0.6 μJ/(μm² sr) in a 10–20 ns pulse, wet biological samples are imaged with about 0.1 μm lateral resolution.