MTL Annual Report

Diffraction gratings and other periodic patterns have long been important tools in research and manufacturing.  Diffraction occurs due to the coherent superposition of waves and is a phenomenon with many useful properties and applications. Waves of many types can be diffracted, including visible and ultraviolet light, x-rays, electrons, and even atom beams. Periodic patterns have many useful applications in fields such as optics and spectroscopy; filtering of beams and media; metrology; high-power lasers; optical communications; semiconductor manufacturing; and nanotechnology research in nanophotonics, nanomagnetics, and nanobiology.

A long-standing problem with transmission gratings in the extreme ultraviolet (EUV) and soft x-ray bands has been the strong absorption of photons upon transmission and thus a low diffraction efficiency in this important wavelength band. We have recently solved this problem with the invention and fabrication of critical-angle transmission (CAT) gratings. This new design for the first time combines the high broadband efficiency of blazed grazing-incidence reflection gratings with the superior alignment and figure tolerances and the low weight of transmission gratings ^[1] [2]. The CAT gratings consist of ultrahigh-aspect-ratio, nm-thin freestanding grating bars with sub-nm smooth sidewalls that serve as efficient mirrors for photons incident at graze angles below the angle for total external reflection (see Figures 1 and 2).  Blazing can concentrate diffracted power into a single or a few desired diffraction orders and has been confirmed through x-ray tests.  Blazing also enables the use of higher diffraction orders and leads to manifold increases in spectral ^[3] and spatial resolution in spectrometer or focusing applications, respectively. We have achieved grating bar aspect ratios of ~ 150 in 6-micron-deep, 200-nm-period CAT gratings and are currently focusing on the minimization of internal support structures.

Work on high-resolution (R ~ 10,000 – 100,000) applications is also ongoing in the areas of high-precision patterning of silicon-immersion echelle gratings in infrared telescopes for astronomy ^[4] and blazed reflection gratings for high-resolution EUV and soft x-ray synchrotron applications ^[5].

1. R.K. Heilmann, M. Ahn, E.M. Gullikson, and M.L. Schattenburg, “Blazed High-Efficiency X-Ray Diffraction via Transmission through Arrays of Nanometer-Scale Mirrors,” Optics Express, vol. 16, pp. 8658-8669, June 2008. [↩]
2. M. Ahn, R. K. Heilmann, and M. L. Schattenburg, “Fabrication of 200 nm period blazed transmission gratings on silicon-on-insulator wafers,” Journal of Vacuum Science and Technology B, vol. 26, pp. 2179-2182, Dec. 2008. [↩]
3. R.K. Heilmann, et al., “Development of a critical-angle transmission grating spectrometer for the International X-Ray Observatory” in Proceedings SPIE 7437, 2009, 74370G. [↩]
4. J.P. Marsh et al., “Fabrication and performance of silicon immersion gratings for infrared spectroscopy,” in Proceedings SPIE 6269, 2006, 62694J. [↩]
5. D.L. Voronov et al., “5000 Groove/mm multilayer-coated blazed grating with 33% efficiency in 3^rd order in the EUV wavelength range,” in Proceedings SPIE 7448, 2009, 74480J. [↩]