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Beamline
4.0.2 was the first beamline
at the ALS to provide soft x rays of variable
polarization using an elliptically polarizing
undulator (EPU).
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The
EPU magnet configuration consists of four
quadrants. In addition to varying the gap
changing the field strength it is possible
to move two quadrants along the electron beam
direction. This causes a change in field direction
(as well as in the field strength) and with
that in polarization of the emitted radiation.
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BL4.0.2
EPU during installation.
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Schematic of EPU magnet configuration.
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+EPU
parameters:
+ pure permanent magnet device
+ period length of 5 cm, 33 periods
+ device length of 1.85 m
+ minimum gap 14 mm
+The
polarization can be switched from left to
right
circularly polarized within 2 seconds (17 mm/s) and is under full user
control.
+
The
minimum energy the device can achieve
depends on the polarization:
+ horizontal polarization: 85 eV
+ vertical polarization: 165 eV
+ circular polarization: 125 eV
+ full range of linear polarization: 210 eV
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 Schematic of beamline 6.3.1 at the ALS along with the most basic
characteristics.
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+
The
beamline is equipped
with a variable-included angle, plane
grating monochromator
covering the range from 20 eV
to 2000 eV.
+
The resolving
power E/dE is
5000 at 870 eV,
7500 at 400 eV,
>20,000 at 64 eV.
+
At
the transition metal L edges (600 –
1000 eV) the photon
flux is about 3x10^12 ph/s/0.1%BW.
+
The
spot size at the sample is currently (Dec.
2006) 60 um vertically and 850 um horizontally.
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Links:
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ALS BL 4.0.2 -
Technical Specifications
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References:
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A.T.
Young, J. Feng, E. Arenholz,
H.A. Padmore, T. Henderson, S. Marks, E.
Hoyer, R. Schlueter,
J.B. Kortright, V. Martynov,
C. Steier, and G. Portmann
First commissioning results for the elliptically polarizing undulator beamline at the
Advanced Light Source
Nucl. Instr. and Meth. A 467-468, 549 (2001).
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A.T.
Young, E. Arenholz, F. Jun, H. Padmore, S. Marks, R. Schlueter,
E. Hoyer, N. Kelez, and
C. Steier
A soft x-ray undulator beamline at the Advanced Light Source with circular
and variable linear polarization for the spectroscopy and microscopy of
magnetic materials
Surf. Rev. Lett. 9, 549 (2002).
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A.T.
Young, E. Arenholz, S. Marks, R. Schlueter, C. Steier,
H.A. Padmore, A.P. Hitchcock, and
D.G. Castner
Variable linear polarization from an X-ray undulator
J. Synchrotron Rad. 9, 270 (2002).
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Contact:
Elke Arenholz (earenholz@lbl.gov)
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