Method of Generating Monochromatic Soft X-ray with Small Focal Spot

In this paper, we present a method of generating monochromatic soft X-rays with a small focal spot. We used transmission metal targets bombarded by electrons to generate L X-rays. We developed the transmission targets by optimizing the incident electron energies and the target thicknesses. We surveyed optimal conditions for monochromaticity, for Ag and Mo targets, by Monte Carlo simulation (EGS4). The results predicted that monochromatic L X-rays are obtained by setting the target thickness to about 100 times the electron range and the electron energy to slightly less than 2 times the L X-ray energy. We estimated the size of the focal spot of monochromatic X-rays to be 4 mum (FWHM) at an electron energy of 5 keV, for a target thickness of 5 mum. For the Mo target, we experimentally confirmed that these conditions were optimal. Experimental spectra matched simulated spectra well, except for the higher energy region.