For the first time, X-ray scientists have access and independent control of ultra-short two-color X-ray pulses with nearly the full peak power of the LCLS (above 50 GW). This new capability represents an improvement by an order of magnitude over what was possible before making it easier and faster for scientists to better dissect hard-to-study chemical and material science samples as well as map medically important proteins, such as signaling proteins of interest as pharmaceutical targets.

At the LCLS, researchers have demonstrated the generation of two-color X-ray pulses using twin electron bunches. In this technique, two electron bunches are generated by illuminating the injector photocathode with a train of two laser pulses separated in time by a few picoseconds. After being accelerated and compressed, the two electron bunches are spaced by tens of femtoseconds and have two distinct energies. When the high brightness bunched electron beams are delivered to a sequence of alternating magnets called an undulator, the two bunches emit two independent X-ray pulses of different photon energies.

The energy difference and the arrival time delay of the two pulses are controllable independently, which enables the study of dynamical processes excited by X-rays at the femtosecond time scale. The existing hard X-ray self-seeding system can be employed to simultaneously filter the two pulses generated by the twin bunches, allowing the generation of two narrow-bandwidth X-ray laser pulses with a wide energy separation. This enables the 3-D structural determination of previously unmapped proteins using femtosecond serial crystallography at LCLS.

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The above post is reprinted from materials provided by Department of Energy, Office of Science. Note: Materials may be edited for content and length.