Extreme-Ultraviolet Efficiency Measurements of Freestanding Transmission Gratings
D R. McMullin, D L. Judge, Charles Tarrio, Robert E. Vest, F Hanser
We report the results of transmission and diffraction measurements at EUV wavelengths (4-30 nm) for two gratings, one with a line density of 5000 mm-1 and the other 2500 mm-1. Measurements were made to provide absolute transmission efficiency at central, first, and when possible, second orders of diffraction. Additionally, measurements were taken to investigate possible guided-wave phenomena at non-normal angles of incidence and a difference between forward and reverse transmission. We find that in first order the 2500 mm-1 grating has almost a factor of two higher diffraction efficiency than the other, and thus should be more appropriate for use in experiments in which greater signal is more important than grating dispersion. We find some sensitivity to forward vs. reverse transmission. The 2500 mm-1 is not sensitive to small deviations from normal incidence, however the 5000 mm-1 grating is. This can be explained by differences in aspect ratio resulting in guided-wave effects.