'Sub-Bragg diffraction' is what researchers at the Complex Photonic Systems group of the University of Twentes MESA+ Institute for Nanotechnology call their surprising observations. An energy dip can also occur when reflection takes place in regular crystal structures at ultra-low energy frequencies . Theoretically, the lowest energy at which this can take place has been unshakably fixed for almost a century, as predicted in the so-called Bragg conditions.
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