A synchrotron light source is a giant scientific facility made to generate X-rays. We wondered what X-rays could be useful for. It turns out they have just the right wavelength to figure out the location of atoms in a solid material.
X-rays with their wavelengths lined up strike the sample material at some angle, and they get bounced off elastically by the electrons in the atoms. Then you detect the bounced off X-rays at the same angle.
At some special angles, X-rays bouncing off different atoms will overlap, but their wavelengths might not line up anymore. You Clear Scientists know that overlapping light waves interfere with each other. And from this interference, you can use geometry to figure out the atomic spacing (5 nm in this example).