Category Physics

Using SLAC’s instrument for ultrafast electron diffraction, researchers were able to directly see the motions of atomic nuclei in vibrating molecules for the first time. In the experiment, a laser pulse (green) hit a spray of iodine gas (at right). This stimulated vibrations in the iodine molecules, which consist of two iodine atoms connected via a chemical bond (top left). The molecules were then hit by an electron beam (blue), generating a characteristic diffraction pattern (background) on a detector, from which the separation of the nuclei can be precisely determined. Credit: SLAC National Accelerator Laboratory

Artistic depiction of the generation of three correlated photons from quantum vacuum. Credit: Antti Paraoanu

It is now possible for machines to learn how natural or artificial systems work by observing them, without being told what to look for

An illustration shows what happens in a typical experiment with SLAC’s LCLS X-ray laser, top, versus what happened in this study with an especially intense X-ray pulse. Normally the X-ray pulses — which are shown coming in from the right — scatter off electrons in a sample and produce a pattern in a detector. But when researchers cranked up the intensity of the X-ray pulses, the pulses seemed to go straight through the sample, as if it were not there, and the pattern in the detector vanished. Two recent papers describe and explain this surprising result, which is due to a ‘nonlinear’ effect where particles of X-ray light team up to cause unexpected things to happen. Credit: SLAC National Accelerator Laboratory