The stronger the light, the brighter? But this is not always the case. When a silicon crystal is illuminated with an ultrafast X-ray laser pulse, the more photons fall on the sample, i.e. the higher the beam intensity, the brighter the diffracted image is indeed initially. However, when the intensity of the X-ray beam begins to exceed a certain critical value, the diffraction image unexpectedly weakens.
During the initial phase of X-ray interaction with matter, the incoming high-energy photons rapidly excite not only the "surface" of the atom, but also the deep atom shell electrons located near the nucleus. It turns out that the presence of holes in the deep shell of an atom greatly reduces the atomic scattering coefficient, the amount that determines the strength of the observed diffraction signal.
Our research shows that rapid electronic destruction occurs first before structural damage occurs to the material and disintegration of the sample. Therefore, the last part of the pulse no longer actually ionizes the material.
At first glance, the observed effect does not seem ideal. However, it seems that people can put this finding to good use. Different atoms were observed to react differently to ultrafast X-ray pulses, which could help more accurately reconstruct three-dimensional complex atomic structures from recorded diffraction images.
Another potential application area is to generate laser pulses with extremely short pulse durations. Because the material through which the high-intensity X-ray pulse passes would "truncate" a large portion of the already ultra-short pulse, it could be intentionally used as a "scissors" to produce shorter pulses than those currently produced. If the research is successful, it will drive another breakthrough in the imaging technology of the quantum world.
