{"id":1728,"date":"2010-07-12T14:40:34","date_gmt":"2010-07-12T18:40:34","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=1728"},"modified":"2010-07-12T14:40:34","modified_gmt":"2010-07-12T18:40:34","slug":"nanofabricated-reflection-and-transmission-gratings","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/nanofabricated-reflection-and-transmission-gratings\/","title":{"rendered":"Nanofabricated Reflection and Transmission Gratings"},"content":{"rendered":"

Diffraction gratings and other periodic patterns have long been important tools in research and manufacturing.\u00a0 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.<\/p>\n

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<\/a>]<\/sup> [2<\/a>]<\/sup>. 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).\u00a0 Blazing can concentrate diffracted power into a single or a few desired diffraction orders and has been confirmed through x-ray tests.\u00a0 Blazing also enables the use of higher diffraction orders and leads to manifold increases in spectral [3<\/a>]<\/sup> 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.<\/p>\n

Work on high-resolution (R ~ 10,000 \u2013 100,000) applications is also ongoing in the areas of high-precision patterning of silicon-immersion echelle gratings in infrared telescopes for astronomy [4<\/a>]<\/sup> and blazed reflection gratings for high-resolution EUV and soft x-ray synchrotron applications [5<\/a>]<\/sup>.<\/p>\n\n\t\t