| Abstract: | 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. |
