The Hofstadter Memorial Lectures Monday, April 12, 2010 Professor Joachim Stohr, Director, Linac Coherent Light Source, SLAC National Accelerator Laboratory

The Department of Physics is pleased to announce that the annual Robert Hofstadter Memorial Lectures will be given this year by Professor Joachim Stohr, Director of the LCLS (Linac Coherent Light Source) at SLAC National Accelerator Laboratory.  Joachim Stöhr joined Stanford University and SLAC in January 2000 as Professor of Photon Science after spending nearly fifteen years at the IBM Almaden Research Center. He was the Director of the Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC from 2005 to 2009 before becoming Director of the world’s first x-ray laser, the Linac Coherent Light Source or LCLS.

Dr. Stöhr received his Ph.D. in Physics from the Technical University of Munich, Germany, and after coming to the US focused his research on the utilization of soft x-rays generated at powerful synchrotron radiation sources.  Over the years he pioneered several soft x-ray techniques for exploring the atomic structure and the electronic and magnetic properties of surfaces and thin films. His first book “NEXAFS Spectroscopy” (Springer, 1992) introduced a technique that is widely used today for elucidating the nature of molecular bonds in different environments such as surface complexes, polymer films, biological systems and liquids, often in combination with x-ray microscopy. His second book, “Magnetism – From Fundamentals to Nanoscale Dynamics” (Springer, 2006), which he co-authored with the late H. C. Siegmann, focused on modern aspects of magnetism such as magnetic data storage and spintronics, with emphasis on using time-resolved x-ray imaging methods to explore the dynamics of magnetic nanostructures.

Besides two books, Dr. Stöhr has authored over 250 scientific publications and several patents. He has received several scholarships, is a fellow of the American Physical Society and served on many national and international advisory committees, most notably, the Basic Energy Sciences Advisory Committee of the U.S. Department of Energy.  More information can be found on his website:  http://www-ssrl.slac.stanford.edu/stohr

Evening Public Lecture (8:00 PM on Monday, April 12, 2010) Location: Geology Corner, Rm. 105 The Light Fantastic: Birth of the X-Ray Laser and a New Era of Science Joachim Stöhr SLAC National Accelerator Laboratory Throughout history, observation with sunlight has been the basis for understanding the world around us. In 1895, W. C. Röntgen discovered a new type of “light”, X-rays, which have allowed us to see the previously invisible. Today, x-rays play a key role in medical imaging and collimated x-ray beams produced at synchrotron radiation facilities constitute a powerful research tool for exploring the invisible world of atoms and electrons inside materials. Around 1960, a new kind of visible light source, the LASER, was invented. Lasers have led to a revolution in science and technology. Laser beams have amazing properties; they are very intense, tightly bundled, and can be created as ultrashort pulses.The ordered nature of laser light has verified the concept that light itself consists of quantum objects called photons. The long wavelength of conventional laser photons, however, makes them blind to the important nanoworld. This deficiency is overcome in the X-ray LASER which can reveal details of matter down to the size of atoms. We have now created the first X-ray laser at SLAC National Accelerator Laboratory at Stanford University and my talk tells the story of this facility, the Linac Coherent Light Source or LCLS. I will describe how this 20 year project succeeded in 2009, creating x-ray beams of unprecedented brilliance and ultrashort pulse lengths. LCLS is now available for scientists from around the world to explore scientific dreams in many fields, such as  recording movies of molecular machines, taking snap shots of chemical reactions, revealing the details of how information bits are switched in computers, or capturing the signature of matter in extreme conditions that can only be created for an instance of time. Through its ability of probing matter on the fundamental length and time scales of their atomic and electronic building blocks, LCLS opens a new era of scientific discovery.

Afternoon Colloquium (4:15 PM on Tuesday, April 13, 2010)   Hewlett Teaching Center, 370 Serra Mall, Rm. 201  Birth of the X-Ray Laser:   Movies of the Dynamic Worlds of Atoms and Electrons  Joachim Stöhr  SLAC National Accelerator Laboratory My talk will describe the evolution of modern X-ray sources, culminating in the construction of the world’s first X-ray laser, the Linac Coherent Light Source or LCLS at SLAC. I will describe how this project, proposed by Claudio Pellegrini of UCLA in 1992, succeeded in 2009, creating X-ray beams of unprecedented brilliance and coherence with pulse lengths down to a few femtoseconds and power densities close to boiling the vacuum. LCLS began operation in October 2009 and is now available for scientists from around the world to explore scientific challenges in various fields. The first experiments focused on exploring the interactions of high field, ultrashort x-ray pulses with atoms and molecules. Future studies will involve studies of ultrafast processes in materials and at surfaces, pump-probe studies of chemical reactions with atomic resolution, structural studies of single macromolecules, viruses and cells as well as dynamic studies of molecular machines. Other studies will explore the intrinsic speed limits of future technologies, such as processing of information bits, that are imposed by nature not human ingenuity. Another application is the study of the properties of matter in extreme conditions, such as warm and hot dense matter, which in the laboratory can be created only for an instance of time. More generally, LCLS constitutes a new tool for addressing scientific grand challenges by its ability to probe matter on the fundamental length and time scales of their atomic and electronic building blocks. Dinner at the Faculty Club (Reception 6pm, Dinner in the Gold Lounge7pm, Tuesday, April 13, 2010) For the dinner, please register by April 3, 2010.

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Robert Hofstadter, winner of the 1961 Nobel Prize, was one of the principal scientists who developed the Compton Observatory, and a professor at Stanford University for many  years until his death.

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