Silicon nitride transmission X-ray mirrors

Transmission X-ray mirrors have been fabricated from 300–400 nm-thick low-stress silicon nitride windows of size 0.6 mm × 85 mm. The windows act as a high-pass energy filter at grazing incidence in an X-ray beam for the beam transmitted through the window. The energy cut-off can be selected by adjusting the incidence angle of the transmission mirror, because the energy cut-off is a function of the angle of the window with respect to the beam. With the transmission mirror at the target angle of 0.22°, a 0.3 mm × 0.3 mm X-ray beam was allowed to pass through the mirror with a cut-off energy of 10 keV at the Cornell High Energy Synchrotron Source. The energy cut-off can be adjusted from 8 to 12 keV at an angle of 0.26° to 0.18°, respectively. The observed mirror transmittance was above 80% for a 300 nm-thick film.