Credit: SLAC National Accelerator Laboratory
UED study of laser-induced alignment of molecules in nitrogen gas. The red curve shows how the distribution of molecular orientations in the gas changes over time. (1) Nitrogen molecules, which consist of two strongly bound nitrogen atoms, normally point in random directions when they tumble in a gas. (2) With an extremely short laser pulse, scientists orient the molecules so that they all point in the same direction. (3-6) This ordered state only lasts for a very brief moment before it disperses, but the rotating molecules periodically return to it, forming “molecular echoes” during which the nitrogen molecules align again. During the echoes, the molecules also switch rapidly from being aligned in one orientation to being aligned in another one that is perpendicular to the first (3-4 and 5-6). Using SLAC’s new UED instrument, the researchers have for the first time visualized this ultrafast transition (3-4, UED signals shown at the top) in real time and with atomic resolution.