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. 31           July 11, 1995

Table of Contents


    1. OPERATIONS UPDATE
    2. OPEN HOUSE AT LAWRENCE BERKELEY NATIONAL LABORATORY
    3. MAGNETO-OPTICAL TECHNIQUES EXTENDED INTO THE SOFT X-RAY REGIME
    4. CONTEST -- 1995 USERS' MEETING T-SHIRT AND MUG DESIGNS

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

Beam availability for the last two weeks was 96% overall and 95% during user shifts. Short outages were caused by a blown fuse in a quadrupole power supply, a beamline vacuum interlock trip, and three storage ring rf trips.

Operations summary for July 11 - July 30
1.9-GeV, 260-mA, 320-bunch operations for users:
    July 12, 08:00-16:00
    July 13-16, 08:00-23:15
1.5-GeV, 400-mA, 320-bunch operations for users:
    July 19, 08:00-16:00
    July 20-23, 08:00-23:15
1.0-GeV, 400-mA, 320-bunch operations for users:
    July 26, 08:00-16:00
    July 27-30, 08:00-23:15
Accelerator Physics:
    July 11, 18, & 25, 08:00-23:15
    July 12, 19, & 26, 16:00-23:15
Maintenance:
    July 17 & 24, 08:00-16:00, with startup 16:00-23:15

2. OPEN HOUSE AT LAWRENCE BERKELEY NATIONAL LABORATORY

"Opening Doors to the 21st Century" and "Share the Wonder" are the themes of a special lab-wide open house to be held on Saturday, October 28. The event will showcase LBNL's outstanding people and programs, giving the public a glimpse of their commitment and excitement about their work. A variety of activities are being planned for 10 a.m. to 3 p.m., including tours, displays, and hands-on demonstrations. Everyone is welcome and encouraged to attend -- the open house is designed to appeal to adults, young people, scientists, science students, and non-scientists alike.

This kind of opportunity comes only once every several years at LBNL, so mark your calendars now for a day of exploration. Future issues of ALSNews will give more information on ALS programs for the open house, transportation to the laboratory, and other details as the day draws closer.

3. MAGNETO-OPTICAL TECHNIQUES EXTENDED INTO THE SOFT X-RAY REGIME
(contact: jbkortright@lbl.gov)

Researchers from the Center for X-Ray Optics at LBNL have taken the first measurements of the magneto-optical Kerr effect (MOKE) using soft x-rays, a technique which can provide element-specific information from heterogeneous magnetic samples. With their newly developed spectroscopic polarimeter, Jeff Kortright and Marybeth Rice used x-ray MOKE to measure the hysteresis loop associated with Fe in an Fe/Cr sample. The shape of a hysteresis loop (the closed path traced by a medium's magnetization as a function of an applied magnetic field) reveals valuable information about a material's ability to sustain magnetization and resist reversal of its magnetization. These are key properties of interest in the development of new magnetic materials for use in more advanced disk drive recording heads and data storage media.

When linearly polarized light is reflected off a magnetized medium, its plane of polarization is rotated (known as the Kerr effect). The measurement of MOKE in the visible light region is commonly used to characterize magnetic materials, but the extension of this technique into the soft x-ray regime offers the ability to study element-specific contributions to the net magnetic properties of homogenous and heterogeneous materials. Soft x-ray MOKE can be either bulk sensitive or surface sensitive depending on the incidence angle and photon energy used, thus allowing the study of magnetic properties of surfaces, buried interfaces or layers. MOKE is closely related to magnetic circular dichroism (MCD), which measures differential absorption of left and right circularly polarized light. The nature of the two techniques is very different, however, and they provide complementary capabilities for the characterization of magnetic materials.

The soft x-ray MOKE experiment at the ALS required the development of a tunable linear polarizer, which took the form of a laterally graded multilayer designed to reflect at 45 degrees, the Brewster angle in the x-ray range. This polarizer forms the heart of the spectro-polarimeter used in the experiment. Light for the experiment came through the Beamline 6.3.2 vertical aperture, which selected an incident beam with 99% linear polarization (as measured using the spectro-polarimeter). The sample, an Fe/Cr multilayer mounted within a solenoidal electromagnet, was positioned to reflect the polarized beam into the polarimeter at an incidence angle of 1 degree. The Kerr effect -- the rotation of the beam's plane of polarization as a function of the applied magnetic field -- was measured by means of the polarizer (which was positioned to reflect a particular plane of polarization) and a detector (which recorded the intensity of light reflected by the polarizer). The measured intensity was used to calculate the degree of rotation of the light, which in turn gave a measurement of the amount of magnetization of the sample.

The energy of the incident photons was tuned to the Fe L[3] edge, where magneto-optical rotation associated with Fe is a maximum. The intensity measurements described above gave the shape of the Fe hysteresis loop as a graph of intensity at the detector versus magnetic field at the sample.

Continued work beyond this initial experiment will investigate the extent to which element-specific hysteresis loops can provide a better understanding of the magnetic properties of multi-component materials. The optical rotation techniques used in the MOKE experiment can also be applied to the study of molecules where chiral structure yields natural optical activity.

4. CONTEST -- 1995 USERS' MEETING T-SHIRT AND MUG DESIGNS
(contact: jccross@lbl.gov)

*WHO* will submit the winning design in the ALS T-shirt/mug contest? Will it be a user? (What beamline?) Will it be an ALS staff member? (What group?) Will great bursts of creativity come from outside the ALS community?

*WHAT* will the style be? Humorous? Dramatic? Cubist? Impressionist? Warhol, Picasso, or Matisse? Will it be a users' view of the ALS? A visionary's? A funding agency's?

Most important, *WHEN* will this design be submitted? August 1 is the deadline for designs for ALS T-shirts and mugs to be available at this years Users' Meeting.

We hope this has sparked your imagination and your enthusiasm -- we have very few submissions so far and need your input for a T-shirt and/or mug we will all enjoy! Here are the design guidelines:

T-shirt designs should be no larger than 22 cm high by 28 cm wide (8.5 by 11 inches) and should use four or fewer colors. Mug designs should be no larger than 7.5 cm by 7.5 cm (3 by 3 inches) and should use one or two colors. Rough drawings or concepts are acceptable as well as more polished artwork. The words "Advanced Light Source" or "ALS" must appear somewhere in the designs.

Send your designs by August 1 to:

Jane Cross
Advanced Light Source
Lawrence Berkeley Laboratory, MS 2-400
1 Cyclotron Road
Berkeley, CA 94720
or fax to Jane Cross at (510) 486-7696.