| Tailored terahertz
pulses from a
laser-modulated electron beam
Researchers at the ALS have demonstrated
a new method to generate tunable, coherent, broadband terahertz
radiation from a relativistic electron beam modulated by a
femtosecond laser. Interaction of the ALS electron beam with
a femtosecond laser pulse as they co-propagate through a wiggler
modulates the electron energies within a short slice of the
electron bunch with about the same duration as the laser pulse.
This causes a dispersion of the electron trajectories, and
the bunch develops a hole that emits short pulses of temporally
and spatially coherent terahertz pulses synchronized to the
laser. The technique allows tremendous flexibility in shaping
the terahertz pulses by appropriate modulation of the laser
pulse. Full
story.
Publication about this research: J.M.
Byrd, Z. Hao, M.C. Martin, D.S. Robin, F. Sannibale, R.W.
Schoenlein, A.A. Zholents, and M.S. Zolotorev, "Tailored
terahertz pulses from a laser-modulated electron beam,"
Phys. Rev. Lett. 96, 164801 (2006).
Contact: John Byrd, JMByrd@lbl.gov
Electronic structure
and magnetism
in diluted magnetic semiconductors
The possibility of using electrons' spins
in addition to their charge in information technology has
created much enthusiasm for a new field of electronics popularly
known as "spintronics." An intensely studied approach
to obtaining spin-polarized carriers for data-storage devices
is the use of diluted magnetic semiconductors created by doping
ions like Mn, Fe, or Co having a net spin into a semiconducting
host such as GaAs, ZnO, or GaN. The interaction among these
spins leads to ferromagnetic order at low temperatures, which
is necessary to create spin-polarized carriers. A research
team working at ALS Beamline
4.0.2 and European Synchrotron Radiation Facility Beamline
ID8 made a big leap forward in clarifying the microscopic
picture of magnetism and anisotropy in Mn-doped GaAs by resolving
localized and hybridized d states using angle-dependent
x-ray magnetic circular dichroism (XMCD) measurements. Full
story.
Publication about this research: K.W.
Edmonds, G. van der Laan, A.A. Freeman, N.R.S. Farley, T.K.
Johal, R.P. Campion, C.T. Foxon, B.L. Gallagher, and E. Arenholz,
"Angle-dependent x-ray magnetic circular dichroism from
(Ga,Mn)As: Anisotropy and identification of hybridized states,"
Phys. Rev. Lett. 96, 117207 (2006).
Contact: Elke Arenholz, EArenholz@lbl.gov
Plans for User
Services Building
pass DOE review
Progress toward the construction of a
new User Support Building (USB) took a big step forward as
the project passed a combined Critical Decision (CD) 1, 2,
and 3 review in mid-October. The Department of Energy (DOE)
Office of Project Assessment (SC-1.3) within the Office of
Science (SC) conducts independent technical, cost, schedule,
and management peer reviews of SC construction projects and
large experimental equipment. These reviews are known as "Lehman
Reviews" after SC-1.3 Director, Dan Lehman. As spelled
out in DOE Order 413.3A, passing the CD1–CD3 review
puts the ALS on track to receiving final approval to proceed
with the project.
 Construction
of the USB will involve the demolition of Building 10, a failing
World War II–era building on the southwest side of the
ALS. The new building will include a high bay for the assembly
of experimental apparatus, a seminar room, modern analytical
laboratories, and office space for about 85 occupants and
support for over 2,000 scientific facility users. Many thanks
to the members of the project team, led by Joe Harkins, as
well as Simon Morton, who agreed to serve on the review panel,
and Steve Rossi, who represents the ALS on the project team.
UEC Corner: Election
results
by Clemens Heske
 Dear
ALS Users: Thank you for casting your vote in the recent Users'
Executive Committee (UEC) elections! Please welcome the newly
elected members of the UEC—Peter Fischer and Ken Goldberg
(Center for X-Ray Optics, Berkeley Lab) and Franz Himpsel
(University of Wisconsin-Madison). They will join the UEC
in 2007. Thank you also for approving the changes in the UEC
charter—it now much more accurately describes the various
activities of the UEC.
As you know, the ALS UEC is a group of
elected ALS users that represents the ALS user community,
both toward ALS and Berkeley Lab management, as well as toward
external persons and groups such as members of the Department
of Energy, committees reviewing the ALS, and elected officials
in Washington and elsewhere.
I would like to thank you for giving
me the opportunity to represent your interests as chair of
the ALS UEC. My term expires at the end of December, but next
year, you'll be well represented by the new chair, Tony van
Buuren (vanbuuren1@llnl.gov),
and the new vice chair, Hendrik Ohldag (hohldag@stanford.edu).
Please do not hesitate to contact them or any other member
of the UEC
with questions, comments, suggestions, etc. Best Greetings!
Contact: Clemens Heske,heske@unlv.nevada.edu
Call for general
user proposals:
Due January 3, 2007
The User Services Office is accepting
general user proposals from scientists who wish to conduct
research in the general sciences at the ALS during the running
period from July through December 2007. The deadline for submissions
is Wednesday, January 3, 2007. (This deadline does not apply
to protein crystallography proposals, which have a separate
process and schedule.) To submit a new proposal, go to the
online form, "ALS
General User Proposal and Request for Beamtime."
 If
you have an existing proposal for which you would like to
request beam time during the July through December 2007 cycle,
you must submit a Proposal Renewal Form. Scientists with existing
proposals that are eligible for renewal will receive instructions
on how to request a login and password to access their proposal
information and forms. Proposals can be renewed for up to
three six-month cycles following their initial submission.
After a total of four cycles, a new proposal must be submitted.
The numeric rating for each proposal
will be communicated to the user along with any comments from
the Proposal Study Panel. The cutoff rating for each beamline
in the previous proposal cycle is published on the Web (see
link below). The following resources are available for further
information:
ALS
User Services Administrator
General
user proposals
ALS User Services online
forms
Beamline
information
Proposal
scores for July 2006–January 2007
Contact: alsproposals@lbl.gov
Safety First:
Report from the
ALS Staff Safety Committee
 The
ALS has made significant progress on the recommendations made
by the Berkeley Lab Radiation Safety Committee (RSC) in response
to shielding control incidents in the past year. All high-priority
items have been completed, and the remaining items have either
been completed or have RSC-approved plans. A revised Radiological
Work Authorization (RWA) for the ALS was also approved by
the RSC and has now taken effect.
The ALS Staff Safety Committee remains
very active and has taken on the following initiatives: investigation
of an incident involving the radiation safety shutter at Beamlines
5.3.1 and 5.3.2 after a small light-fixture fire, development
of guidelines for robotic safety, radiation safety procedures
for the x-ray microscopes, standardizing laser safety guidelines
on the floor, and completion of the beamline shielding endpoints.
Facilities Division has made substantial
improvements to its Ground Penetration Permit process and
we will be following that procedure. Note that in some cases,
Facilities will not grant a permit if the scans are incomplete
or show potential utilities too close to the proposed holes.
As a consequence, ALS will try to minimize penetrations in
the floor deeper than 2 inches.
In preparation for the upcoming demolition
of Building 10, we are working to consolidate and reduce the
inventory of chemicals and materials in the current User Chemistry
Lab. While the interim space in the ALS mezzanine is adequate,
it won't have the same storage capacity. Owners of these materials
are encouraged to try to reduce the amounts wherever possible.
Contacts: Jim Floyd, JGFloyd@lbl.gov
John Grinold
takes on role
of Facility Manager
 John
Grinold recently joined the ALS team as the ALS Facility Manager.
The Facility Manager is a new position designed to manage
and supervise the execution of work planning and work controls
processes. He comes to us from the Nationial Ignition Facility
(NIF) project at Lawrence Livermore National Laboratory, where
he was the field manager for switchyard and target area activities
and served as a work control officer. Extremely focused on
working safely, John will be launching new programs for hazard
identification and communication and a new improved work permit
process. John and ES&H manager Jim Floyd will be teaming
up for implementation of strong Integrated Safety Management
(ISM) processes at the ALS. His office is in Bldg. 80, Rm.
157 and his telephone extension is x6826. Please drop by or
call if you have any questions or suggestions.
Holiday closure
schedule
Berkeley Lab will close on the evening
of December 22 and reopen on the morning of January 2. During
the closure, the Lab will shut down as much heating and ventilating
equipment as possible to reduce costs. (The ALS experiment
floor will remain at normal temperature to prevent damage
to sensitive equipment.) The first user run of 2007 will be
January 5–8, following the extended installation shutdown
currently in progress. There will be no December issue of
ALSNews; the next issue will be published on January 31. From
all of us at the ALS, have a safe and happy holiday season,
and we'll see you next year! |
