The atomic and molecular world is abuzz with frenetic motion. Because they are so small and light, molecules and atoms react incredibly quickly to forces that act on them. Chemical reactions, in which atoms and molecules join or split, can take place in mere quadrillionths of a second.
Because all chemistry relies on the extremely rapid motion of electrons and atoms, understanding their behavior on extraordinarily short timescales can reveal clues about how chemical processes unfold. SLAC researchers use a suite of cutting-edge tools to study how atoms move—optical lasers, high-intensity X-rays and, soon, a new kind of X-ray laser, the Linac Coherent Light Source (LCLS).
Photons of light can be used to both observe and control how atoms behave. Infrared photons, for instance, just like all light, exist as both particles and waves. As waves, they take the form of electromagnetic oscillations, a rapid push/pull in the electromagnetic environment that rises and falls extremely rapidly. For visible light, these oscillations occur hundreds of trillions of times per second. Now, SLAC researchers have devised a way of generating photon pulses that can be switched on and off in roughly half the time of one oscillation. The result is only half an oscillation—all of the push, with none of the pull, giving researchers a molecular-scale "hammer" for knocking atoms and electrons around.
Using photons in this way holds promise for probing the atomic-level behavior of many different materials. Within semiconductors, for example, the motion and speed of electrons changes very rapidly. Manipulating and measuring how these electrons move could lead to more efficient solar cells, or could improve the efficiency of hydrogen production from water. Such pulses might also be used to drive ultrafast switches for computer memory, which could dramatically increase computing speed.
The LCLS is a new class of laser used to create extremely intense photon pulses in the X-ray spectrum using a beam of electrons from a particle accelerator. Once it is fully operational, the LCLS will use SLAC's existing linear accelerator to produce laser light that is one billion times brighter than any other X-ray source on earth. Its ultrafast X-ray pulses, lasting less than 100 femtoseconds (1/10 of a trillionth of a second) are ideal for characterizing atomic and molecular processes as they happen.
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