Development of Soft X-Ray Flat-Field Holographic Gratings for the Measurement of K Emission Spectrum of Li

We have developed a wavelength-dispersive soft x-ray spectrograph covering an energy region of 50-4000 eV to attach to a conventional electron microscope. The energy range was properly divided into four ranges of 50-200 eV, 155-350 eV, 300-2200 eV, and 2000-4000 eV, and a versatile spectrograph equipped with interchangeable multiple gratings optimized in the respective energy ranges has been developed. In particular, the grating that covers the 50-200 eV range can be used for the measurement of the K emission spectrum (~55 eV) of lithium. The diffraction efficiency evaluated by synchrotron radiation and resolving power measured by laser produced plasma sources are over 5% and in excess of 700, respectively. The K emission spectrum of metallic Li with high spectral resolution has been successfully observed with the spectrograph attached to a transmission electron microscope.