BL6U

Construction of New Soft X-Ray Spectroscopy Beamline BL6U
E. Shigemasa1, Y. Hikosaka1, E. Nakamura1, N. Kondo1, M. Sakai1, T. Horigome1and K. Amemiya1, 2
1
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan2
Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801, Japan
A refocusing mirror M2 has a toroidal shape, which
focuses the monochromatized radiation at the sample
position.
The practical construction of BL6U has started fromthe summer of 2008. After careful tuning of thewhole system at BL6U, the first light was observed in
December 2008. The performance tests of themonochromator have been performed, whose results
are given in a separate page in this report. High
resolution spectroscopic studies, not only in gas phase,
but in solids or surfaces, are planned to be conducted
there. The constructions of the apparatuses forhigh-resolution electron spectroscopy have also
begun.

Various types of monochromators for synchrotron
radiation have been proposed and constructed torealize vibrational spectroscopy in the soft x-ray range,
which contains the K-shell thresholds of chemicallyimportant elements like C, N, and O, since the firstsuccessful observation for the vibrational structures ofthe π* resonance in the K-shell photoabsorption
spectrum of nitrogen molecules [1]. Thanks to thehigh brilliance offered by undulator radiation, both
high-resolution and high-flux are achievablesimultaneously at a considerable high level. At theUVSOR, there is only one soft X-ray undulator
beamline for high resolution spectroscopy, BL3U, inthe photon energy region of interest.
A new project for constructing the undulator
beamline BL6U has been recently initiated. The
entrance slit-less configuration for the monochromator
has been chosen. In order to cover a wide photon
energy region (30-500 eV) with one single grating, avariable-included-angle Monk-Gillieson mounting
monochromator with a varied-line-spacing (VLS)
plane grating [2] has been selected. Design study forthe monochromator at BL6U has been completed, withthe collaboration of KEK-PF. The monochromator
designed will cover the photon energy ranging from30 to 500 eV, with the resolving power higher than
10000 and the photon flux more than 1010 photons/sec.
The resolution of the present monochromator wasstudied by ray-tracing simulation as well as analyticalestimation. It is found that a resolving power E/∆E ofmore than 10000 is achievable over the energy range
from 30 to 500 eV with one single grating. The
throughput photon flux estimated ranges from 1010 to1012 photons/sec for the ring current of 350 mA, with aresolving power of 10000.
Figure 1 shows the overall picture of the beamline
constructed, with pictorial indications for theincoming undulator radiation and important beamline
components. In front of all optical elements, there isan aperture S0, located 5.0 m from the source position.
The radiation is deflected horizontally by a toroidal
mirror M0 located 1.5 m downstream of the aperture.
M0 converges the radiation vertically onto a virtual
focal point behind the VLS grating G, and thus
converging soft X-rays illuminate G. A plane mirror
M1 is located 1.5 m behind M0. One laminar profile
plane grating, which is ruled holographically, with thevaried-line-spacing (500 l/mm at its center position), isdesigned to cover the energy range from 30 to 700 eV.
The included angle of the grating should be changed
from 167˚ to 176˚ in order to minimize the aberrations.

Fig. 1. Top view of the newly constructed soft
X-ray spectroscopy beamline BL6U.
[1] C. T. Chen, Y. Ma and F. Sette, Phys. Rev. A 40
(1989) 6737.
[2] K. Amemiya and T. Ohta, J. Synchrotron Rad. 11(2004) 171.

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BL6U

Performance of New Soft X-Ray Spectroscopy Beamline BL6U
E. Shigemasa1, Y. Hikosaka1, E. Nakamura1, N. Kondo1, M. Sakai1, T. Horigome1
and K. Amemiya1, 21
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 Japan2Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801 Japan
identified as indicated here. Assuming that thenatural width of the Kr 3d-1 5p Rydberg states is 83
meV [4] and the spectral profile observed isexpressed by a Voigt function, the monochromatorband-pass is estimated to be ~25 meV. Since thetheoretical value is about 10 meV around 90 eV, there
is room for improvement on the resolving power.

The in-vacuum type undulator U6, which has been
relocated from the long straight section U7 to the shortone U6, has 26 magnetic periods and the period lengthis 36 mm [1]. The spectral region from 50 eV to 140
eV, which is realized by changing the gap height from15 mm to 40 mm, was covered with the first harmonic
radiation [1]. There was an inherent energy gap
between the highest and lowest photon energies,
covered by the first and third harmonics, respectively.
Due to the relocation of the undulator, this gap has
been bridged. This is because the vertical betatronfunction at U6 is smaller than that at U7 and theminimum gap available becomes accordingly smaller
down to 10 mm. Correspondingly the tunability
covered by the undulator radiation is widened: thephoton energy range from 30 to 500 eV can be coveredby odd harmonics up to seventh without any energy
gap. Then a new project for constructing theundulator beamline BL6U has recently been initiated.
According to the theoretical estimations by using
the ray-tracing program XRAY-T [2] in combination
with the synchrotron radiation calculation code
named SPECTRA [3], the monochromator designedfor BL6U, which possesses a variable-included angle
mechanism, can cover the photon energy ranging from30 to 500 eV by one single grating, with the resolving
power higher than 10000 and the photon flux morethan 1010 photons/sec. We have carried out shortperformance tests of the monochromator installed.
Figure 1 shows an example of the throughput
spectra measured by a gold plate located just after theexit slit. Here the exit slit opening and the undulator
gap were set at 30 µm and 22.5 mm, respectively.
The included angle was fixed at 171°, whichcorresponds to the optimum condition for 80 eV.
The measured photocurrent has been converted to thephoton flux, by assuming that the quantum yield of
Au is equal to 3% in the entire photon energy range
of interest. The slit opening of 30 µm corresponds
to E/∆E ~ 10000 at 80 eV. It is found that thephoton flux of the fundamental peak around 100 eV
goes over 1 × 1012 photons/sec. The photon flux inthe high energy region may be improved, by changing
the included angles as satisfying their optimums
during the photon energy scanning.
Figure 2 displays a total-ion yield spectrum in thevicinity of the 3d ionization thresholds of Kr,
measured by an imaging spectrometer. The slit
opening and undulator gap were the same as theabove measurement.
Two Rydberg series
converging to the 3d ionization thresholds areFig. 1. Estimated throughput spectrum from theVLS-PGM at BL6U.

Fig. 2. Total-ion yield curve measured in the regionof the 3d subshell of Kr.
[1] A. Mochihashi, M. Katoh, M. Hosaka, K. Hayashi,
J. Yamazaki, Y. Takashima, Y. Hori, H. Kitamura, T.
Hara and T. Tanaka, AIP Conf. Proc. 705 (2004) 259.
[2] K. Amemiya, H. Kondoh, T. Yokoyama and T.
Ohta, J. Electron Spectrosc. Relat. Phenom. 124(2002) 151.
[3] T. Tanaka and H. Kitamura, J. Synchrotron Radiat.
8 (2001) 1221.
[4] O.-P. Sairanen, A. Kivimäki, E. Nõmmiste, H.
Aksela and S. Aksela, Phys. Rev. A 54 (1996) 2834.

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BL7U

Present Status of UVSOR-II BL7U for VUV Angle-Resolved Photoemission
Spectroscopy of Strongly Correlated Electron Systems
㩷 T. Ito1, 2, M. Sakai1, E. Nakamura1, N. Kondo1 and S. Kimura1, 2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
2
School of Physical Sciences, the Graduate University for Advanced Studies (SOKENDAI),
Okazaki 444-8585, Japan
1

BL7U, the VUV angle-resolved photoemission(ARPES) beamline for advanced studies of strongly
correlated electron systems, has been constructed inFY2006 and opened for users in FY2007 [1]. To
satisfy the needs from users, especially (1) higher
photon-flux, (2) reduction of higher-order light and(3) better base pressure of the photoemission chamber,
we have improved the beamline in FY2008. As aresult, we successfully achieved the sufficientthroughput for ARPES experiments.
To improve the photon-flux especially at thebulk-sensitive low photon-energy (hν < 15 eV), weupdated the lowest photon-energy grating G3 from
Au-coating to SiC-coating one. After the update ofG3, we realign the beamline to be optimized with thecenter of the undulator light. As a result, the photon
flux as well as the focusing at the sample position has
intensively been improved than that in FY2007.
Figures 1(a), (b) and (c) show the improved
throughput spectra obtained at low (red line)-,medium (red line)-, and high (red, yellow, green, bluelines)-photon energy regions compared with theprevious one (black lines), respectively. At eachenergy region, the spectrum becomes sharper andshifts to the higher energy side in the same condition,
indicating successful alignment with the optimum
parameter of the undulator light. Clear vibration
sub-bands observed higher and lower energy side of
the main peak of the throughput spectrum (Fig. 2),
which is consistent with a calculation, ensures thecorrect alignment getting the center of the undulator
light.
To reduce the intensity of higher order light at thelow photon-energy region, we equipped a VUV filterof MgF2 just after the exit slit. As a result, we
successfully reduced the higher-order light abovehν = 11 eV (see Fig. 3). Typical loss of efficiency by
the filter is less than 10%, which ensures sufficientthroughput for VUV ARPES experiments withbulk-sensitive low-photon energies.
Finally, to improve the base pressure at the sample,
we added a cryopump (ULVAC Cryogenic Inc., U8H)
and an ion pump (ULVAC, PST-200CX2) to thephotoemission chamber. As a result, we achieved thebase pressure of 5 × 10-9 Pa better than before (2 ×10-8 Pa). For further improvement of base pressure,
we plan to equip a thermal radiation shield around thesample in FY2009.

Fig. 1. Improvements of throughput spectra before
and after the realignment of optics at BL7U.

Fig. 2. Throughput spectrum at low photon-energy
region in comparison with the calculation.

Fig. 3. Throughout spectra with some undulator gap
size with and without a VUV filter, MgF2, in the low
photon-energy region.
[1] S. Kimura et al., AIP Conf. Proc. 879 (2007) 527.

41