High precision alignment of x-ray transmission diffraction gratings
Gold transmission diffraction gratings used for x-ray spectroscopy must often be aligned rotationally to within submilliradian accuracy of an instrument axis. Currently, these gratings have a high line density (grating periods less than 300 nm) so conventional techniques (such as optical imaging or diffraction) which have been used previously to determine the grating orientation cannot work. Other techniques (such as polarization effects) give <1-mrad accuracy. We describe here a simple technique that allows one to produce an optically observable alignment mark that is oriented parallel to the grating direction within a few microradians. We ''write'' a line, approx.0.01-mm wide, directly on the grating by exposing an electron-beam-sensitive coating of polymethylmethacrylate (PMMA) on the grating while driving the grating through the beam of a scanning electron microscope (SEM). The direction of motion is made parallel to the grating lines by controlling the stage motion with a joystick while inspecting the grating in the SEM. Using the joystick, one can ''follow'' a single grating line from end to end. The SEM written line is made a permanent addition to the grating by ion-beam etching or gold microplating, and can later be used for in situ alignment verification. Our lines have been made parallel to the original grating lines to approximately +- 5 ..mu..rad; this alignment can be extended to +- 1 ..mu..rad. Standard optical techniques can be used to align the grating with respect to an arbitrary instrument axis. This technique works equally well with transmission and reflection gratings.
- Research Organization:
- University of California, Lawrence Livermore National Laboratory, Livermore, California 94550
- OSTI ID:
- 5366402
- Journal Information:
- Rev. Sci. Instrum.; (United States), Vol. 59:3
- Country of Publication:
- United States
- Language:
- English
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