ALSNews is a biweekly electronic newsletter to keep users and other interested parties informed about developments at the Advanced Light Source, a national user facility located at Lawrence Berkeley National Laboratory, University of California. To be placed on the mailing list, send your name and complete internet address to ALSNews@lbl.gov. We welcome suggestions for topics and content.

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ALSNews           Vol. 70           February 5, 1997

Table of Contents


    1. OPERATIONS UPDATE
    2. FEMTOSECOND X RAYS GENERATED AT BEAM TEST FACILITY
    3. FIRST LIGHT TO MICRO-XPS BRANCHLINE
    4. REVISED ALS SAFETY HANDBOOK AND NEW USER ADVISORY NOW AVAILABLE 
    5. PROTEIN CRYSTALLOGRAPHY FUNDING -- THE BIG PICTURE

1. OPERATIONS UPDATE
(contact: rmmiller@lbl.gov)

Beam reliability for the last two weeks was 90.2% overall and 88.9% for user shifts. The user shift average was affected by the increased fill time for the camshaft-fill run last week.

Operations Summary for February 5 - February 24

Feb 05, 00:00-08:00           User scrubbing & special operations
Feb 05, 08:00- Feb 10, 07:15  1.9-GeV/340-mA/304-bunch user operations
Feb 10, 07:30-24:00           Maintenance & startup
Feb 11, 00:00-24:00           Accelerator physics
Feb 12, 00:00-08:00           User scrubbing & special operations
Feb 12, 08:00- Feb 17, 07:15  1.5-GeV/400-mA/304-bunch user operations
Feb 17, 07:30- Feb 18, 07:30  Presidents' Day holiday - no operations
Feb 18, 07:30-24:00           Maintenance & startup
Feb 19, 00:00-24:00           Accelerator physics
Feb 20, 00:00-08:00           User scrubbing & special operations
Feb 20, 08:00- Feb 24, 07:15  1.9-GeV/340-mA/304-bunch user operations

2. FEMTOSECOND X RAYS GENERATED AT BEAM TEST FACILITY
(contacts: rwschoenlein@lbl.gov and leemans@lbl.gov)

Materials scientists have long been interested in using very short pulses of x rays to study phenomena that occur on similarly short time scales. Chemical reactions, phase transitions, and surface processes are among the interactions ultimately governed by the motion of atoms on the time scale of a single vibrational period, about 100 femtoseconds (1 fs = 10**-15 second). Laser pulses this short have been available in the visible-light region of the spectrum, but probing atomic structure (as opposed to extended electronic structure) calls for x-ray pulses. Recently, a research group led by Robert Schoenlein (Berkeley Lab Materials Sciences Division) and Wim Leemans (Berkeley Lab Center for Beam Physics), using the Center for Beam Physics' Beam Test Facility at the ALS, produced x-ray pulses just 300 fs long at a wavelength of 0.4 angstroms.

The group generated these ultrashort pulses by directing 100-fs pulses from a terawatt infrared laser across the relativistic electron beam from the ALS linear accelerator (linac) at a 90-degree angle, with laser and electron beams both focused tightly at the intersection point. In this arrangement, some of the infrared photons interact with electrons and are scattered. The scattered photons have x-ray energies and travel in the same direction as the electron beam. Downstream from the point of intersection, a bend magnet diverts the electrons so that the x-ray pulses can be directly accessed. Such experiments do not interfere with the more conventional uses of the ALS, since the linac is needed to inject electrons into the storage ring only for a few minutes of each shift. (A schematic illustration of the experimental setup is available on the World Wide Web here.)

The idea of obtaining short-wavelength photons by scattering longer-wavelength laser light from a relativistic electron beam is decades old. The particular approach described above for generating femtosecond x-ray pulses was proposed more recently by Swapan Chattopadhyay and Kwang-Je Kim of Berkeley Lab's Center for Beam Physics. Earlier ideas and experiments involved laser light and electrons approaching each other in directly opposite directions, but this geometry results in a pulse length comparable to that of the electron beam, which at the ALS is several picoseconds (1 ps = 10**-12 second). However, if the laser and electron beams cross at 90 degrees, the transit time of the light through the beam determines the length of the scattered x-ray pulses, and this transit time is reduced by focusing the electron beam so that the area of interaction has a diameter of only 90 microns.

The researchers plan to shorten the x-ray pulses to about 50 fs by focusing the electron beam more strongly using plasma-based lenses. They will also attempt pump-probe experiments using laser-excited samples, to study changes in the long-range order of materials by observing the time evolution of their Bragg-diffraction peaks (generated by reflection from planes of atoms within a crystal). The brightness already achieved (~2 x 10**5 photons/s/sq. mm/sq. mrad in a 15% bandwidth) is sufficient for these experiments. An important long-term goal, however, is to use time-resolved EXAFS (extended x-ray absorption fine structure) spectroscopy to study changes in short-range order associated with chemical reactions. Substantial but realizable improvements, primarily in linac technology, could provide nearly 10**11 photons/s/sq. mm/sq. mrad in a 3% bandwidth, bright enough for such studies. In another area, the research group is using the x-ray pulses to probe the size and divergence of 100-fs slices of electron bunches. This kind of characterization will become increasingly important at advanced accelerators with bunch lengths in the sub-picosecond range.

Femtosecond x-ray work was conducted by W.P. Leemans (co-principal investigator), P. Volfbeyn, M. Zolotorev, K.J. Kim, and S. Chattopadhyay (Berkeley Lab's Center for Beam Physics); R.W. Schoenlein (co-principal investigator) and T.E. Glover (Berkeley Lab's Materials Sciences Division, or MSD); A.H. Chin (University of California at Berkeley); C.V. Shank (MSD and UC Berkeley); and P. Balling (University of Aarhus, Denmark).
Funding: Office of Basic Energy Sciences of the U.S. Department of Energy, National Science Foundation.

Publications about this experiment:
R.W. Schoenlein, W.P. Leemans, et al., Science 274 (1996), p. 236.
W.P. Leemans, R.W. Schoenlein, et al., Phys. Rev. Lett. 77 (1996), p. 4182.
W.P. Leemans, R.W. Schoenlein, et al., IEEE Journal of Quantum Electronics 33 (1997), pp. 1925-1934.

3. FIRST LIGHT TO MICRO-XPS BRANCHLINE
(contact: trrenner@lbl.gov)

In the early morning of January 23, the micro x-ray photoemission spectroscopy (micro-XPS) branchline on Beamline 7.3.1 received its first light from the ALS. A change in the monochromator grating angle was the only adjustment required to steer light through the beamline and strike a phosphor target at the end of branchline 7.3.1.2. Both zero-order and dispersed light reached the target. Thorough engineering and precise survey and alignment work were credited for the smooth inauguration. The next milestone for the branchline will be characterization of the monochromator (measurements of energy resolution, flux, and beam size and stability). This work is already under way, and plans call for having light to the micro-XPS endstation within the next two weeks.

The micro-XPS endstation was created specifically for analyzing the microstructures in integrated circuits (ICs) and the silicon wafers from which ICs are made (see the next edition of ALSNews for a more detailed description of the branchline). The project was started only 10 months ago, and meeting this very tight manufacturing and commissioning goal was of key importance for the industrial partners. Sustained support from the Berkeley Lab fabrication shops made it possible to meet this demanding schedule. The micro-XPS project is led by Tim Renner and Zahid Hussain, supported by an engineering/design team led by Rob Duarte, Keith Franck, and Pat McKean and a technician team led by Greg Morrison.

Participating research team spokesperson for branchline 7.3.1.2: Baylor Triplett, Intel.
Funding for Beamline 7.3.1: IBM, Intel, and the U.S. Department of Energy.

4. REVISED ALS SAFETY HANDBOOK AND NEW USER ADVISORY NOW AVAILABLE
(contact: alsuser@lbl.gov)

In keeping with the ALS commitment to a safe workplace for everyone, a revised and improved ALS Safety Handbook and a new advisory covering the use of radioactive materials at the ALS were issued this week. The ALS Safety Handbook, edited by Joan Minton and Elizabeth Moxon, provides safety guidelines for anyone working at the ALS and covers everything from the documentation required for an experiment to the safe handling of hazardous materials. Contact numbers are also included so staff and users can readily obtain any additional information or technical assistance required to ensure the highest level of safety in our workplace.

A new User Advisory, "The Use of Radioactive Materials at the ALS (ALS Advisory 16)," details Berkeley Lab and ALS policy regarding the documentation, transportation, and storage of prepared, radioactive targets intended for experimental use at the ALS. The advisory also outlines the circumstances under which additional safety training would be required and provides contacts for additional information.

The ALS Safety Handbook and User Advisory 16 are available from the ALS User Office [Tel: (510) 486-7745, Fax: (510) 486-4773, Email: alsuser@lbl.gov]. User Advisory 16 is also posted on the World Wide Web.

5. PROTEIN CRYSTALLOGRAPHY FUNDING -- THE BIG PICTURE

When, in the last issue of ALSNews, we reported on first light to the first portion of the protein crystallography beamline, we also reported on recent commitments of funding for the beamline's second branchline and endstation. To avoid any confusion arising from the pairing of these two pieces of news, we offer here a clarification of the beamline's funding.

The initial portion of the beamline, including the wiggler, front end, and first branchline and endstation, was funded by the U.S. Department of Energy's Biological and Environmental Research Program (BER, administered by the Office of Health and Environment Research) and by the University of California through Berkeley Lab. (This initial funding was reported in ALSNews Vol. 10, January 24, 1995.) It was part of this first portion of the beamline, from the wiggler to just before the monochromator, that received first light in December. BER also funded the construction of the Structural Biology Support Facilities, a complex of laboratories and offices located near the beamline.

About half the funding for the beamline's second branchline and endstation has recently been committed by Amgen, Roche Biosciences, UC Berkeley, and Berkeley Lab matching funds.