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In this issue:
Sensing the Energy: Calibrating the LCLS
Science Today: Small, Fast and Holographic
Trailer Re-warming Party Today!
At the LHC: Fabiola Gianotti to Take ATLAS Helm
Reminder: B34 Plumbing

SLAC Today

Thursday - September 25, 2008

Sensing the Energy: Calibrating the LCLS

(Photo - sensor)
The LCLS total energy sensor will sit directly in the X-ray beam during commissioning to help calibrate diagnostic equipment. (Photo by Brad Plummer. Click for larger image.)

The Linac Coherent Light Source will generate X-rays 10 billion times brighter than any source before it. Being the first of its kind, the LCLS has presented engineers with a number of unique technical hurdles. Measuring just how much punch the LCLS beam actually packs has proved especially challenging. But a team of LCLS scientists and engineers led by Stephan Friedrich at Lawrence Livermore National Laboratory has solved the problem with a tiny sensor designed to confront the beam head on.

The power contained in a single pulse from the LCLS is estimated to contain in the neighborhood of a few billion watts—a tremendous amount to be sure. However, that power will be compressed into an unimaginably tiny sliver of time: around 100 femtoseconds, or one-tenth of a quadrillionth of a second. Because the pulses are so short, the total energy of the beam is relatively low, about 2 millijoules.

Despite their brevity, the momentary burst of X-rays still packs enough punch to instantaneously destroy most materials, a critical consideration for sensor design. Additionally, the sensor must be able to measure pulses at the full repetition rate of 120 per second.  Read more...

(Daily Column - Science Today)

Small, Fast and Holographic

Key components of the proposed ultrafast stop watch. (a) A pump laser pulse excites the sample from an angle. (b) An ultrafast X-ray pulse illuminates the sample and the scattering is detected as a hologram.

Panoramic images are captivating in any form, with their wide field of view and extremely high resolution. Now, scientists at the Stanford Synchrotron Radiation Laboratory have demonstrated a new X-ray holographic technique for imaging wide areas of a nanoscale sample without losing resolution. The results were published in the November 2007 Optics Letters.

A similar technique using light of visible wavelengths was demonstrated at Stanford more than 50 years ago, as a means of improving holographic images distorted by atmospheric disturbances. With X-rays, the finite size of the pixels in the detector blur resolution. In a hologram, this translates to a smaller field of view in the reconstructed image. To overcome this limitation, the team strategically arranged a collection of reference points on the sample to increase the effective field of view, which counters the smearing otherwise caused by the detector.

The team used the soft X-ray coherent scattering capabilities of Beamline 5–2 (now BL13–3) to image a nanostructured, 1 micron-thick gold film. Four individual arrow shapes spanning one fifth of a millimeter were milled through the film, with a strategically-placed reference point next to each arrow. The reconstructed image showed all four arrows with 50-nanometer resolution.

The new technique could prove particularly useful for studying ultrafast processes using X-ray free electron lasers such as the Linac Coherent Light Source.

To learn more about this research, see the full scientific highlight.

Trailer Re-warming Party Today!

Come to the Building 267 parking lot between 2:30 and 4:30 for munchies and merriment. This is a great chance to thank HR Director Lee Lyon for his years of excellent service and welcome Communications Director Rob Brown to SLAC.

At the LHC: Fabiola Gianotti to Take ATLAS Helm

(Photo - Fabiola Gianotti)
Fabiola Gianotti. (Photo courtesy of Fermilab Today.)

When Fabiola Gianotti first traveled to CERN as a young post-doc in the early 1990s, she was overwhelmed by the laboratory's international culture.

Starting March 1, 2009, she'll help lead that international community as she takes the reins as the ATLAS collaboration's new spokesperson.

"Clearly this is a role for which she has been training," said Fermilab theorist and colleague Chris Quigg. "From my perspective, the important characteristics in this position are a good physics sense and an effective manner with people. Fabiola has both. ATLAS has chosen well."

Gianotti, who has served as ATLAS physics coordinator from 1999 to 2003 and has worked with the collaboration since its inception, will take over from Peter Jenni, who will step down after 15 years.

"Clearly it is a big honor and big responsibility. Peter has given the most crucial contributions to develop and shape the collaboration," Gianotti said.

Jenni plans to get back to more hands-on physics, including helping to run the detector.  Read more on Fermilab Today...

Reminder: B34 Plumbing

A quick reminder for SLAC staff: please do not use any sink, toilet or shower in Building 34. Repair of a broken sewer pipe is underway, with completion expected in the coming weeks. Check back here for updates.

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