BL2B+㩷 㩷 Trajectory Simulations of C58 from C60 in the VMI Spectrometer
B. P. Kafle1, Md. S. I. Prodhan1, H. Katayanagi1, 2 and K. Mitsuke1, 2                
Dept. Photo-Molec. Sci., Inst. Molec. Sci., Okazaki 444-8585, Japan      
2Graduate Univ. Adv. Studies (SOKENDAI), Okazaki 444-8585, Japan
1

Figure 1 shows the simulated velocity map imagesof C58+ ions on the PSD at the kinetic energies of 0.1
eV (|) and 0.11 eV (). It should be noted that theseimages result from momentum distributions of the ionsin the laboratory system. We took into account the ion
trajectories generated in the elevation and azimuth
angle ranges of 0° to +90° and 0° to +180°,
respectively, which cover only one quarter of the full
3D trajectories over the 4S solid angle. The
trajectories with a given elevation angle form ahorizontal stripe, and the envelope of all the stripes
makes an arc, which clearly demonstrates thatscattering distribution in spherical symmetry can be
successfully projected on an image plane. It is likelythat C58+ fragment ions with kinetic energy differenceof 0.01eV are almost separable. Comparison between
the simulations with and without the mass gate and ionreflector confirmed that the images are not distorted in
the presence of these devices.

The performance of the mass-selective velocity
map imaging (VMI) spectrometer has been studied by
the computer simulation of the ion trajectories, by
taking an example of C58+ from C60.
The geometry of the VMI spectrometer is given in[1] and is essentially the same as that in [2]. The lenssystem contains three square electrodes, viz. repeller,
ion extractor and tube entrance, all of which have thesides of 50 mm and the internal diameters of 20 mm.
The central holes of the latter two electrodes have nomesh. Such open-hole structures have enabled us tobend the equipotential surfaces simply by
manipulating the ion-extractor voltage and to achieve
the excellent focusing of the PSD image.
We performed ion trajectory simulations utilizing
the SIMION 3D software [3] to optimize thedimensions of the electrodes. Here, dissociative
ionization of C60 was considered to take place withina region of rectangular parallelepiped ¨x¨y¨z =1×3×1 mm3. The y-direction was assigned to thepassage of SR, so that it ranges from -1.5 to +1.5 mm.
The eight corners and center of the ionization region
were chosen for the starting points of the ion flights.
From each point 171 trajectories were generated in
the range of the elevation angle T from – 90q to + 90q
at intervals of 22.5q and in the range of the azimuth
angle I from 0q to + 180q at intervals of 10q (see [2]).
Application of the pulse voltages to the repeller andmass gate (VR and VG, respectively) has been realized
by means of a “user program” of SIMION [3]. Thebase line values of all the pulse voltages were 0 V. The
amplitude and duration of VR were 300 V and 7 μs,
respectively. At the same time a pulse voltage with theamplitude of 214 V was applied to the ion extractor.
Such applications permit the ions produced during thepast 13 Ps to be guided into the drift tube. To filter C58+
ions we set the timing of VG at 44.5 Ps later than that of
VR. At the mass gate the spread of the TOF of C58+ wasestimated to be 0.65 μs which arises from the finite
volume of the ionization region and distribution of the
kinetic energy of the fragment ions. Thus, theamplitude and duration of VG were set to 120 V and 1
μs, respectively. A continuous voltage of 320 V wasapplied to the retarding grid of the ion reflector.
Most of the simulated trajectories of C58+ were
found to go beyond the retarding grid and reach the
PSD, whereas the trajectories of C60+ and C56+ werereflected completely. This observation may provide
evidence for exclusive imaging detection of C58+
without interference from the neighboring ions, C60+
and C56+, with the same kinetic energies.

Fig. 1. Simulated 2D images of the 3D velocity
distribution of C58+ from C60 projected on the PSD.
The initial kinetic energies of C58+ were set to 0.1(|) and 0.11 eV ().
[1] H. Katayanagi, B. P. Kafle, C. Huang, Md. S. I.
Prodhan, H. Yagi and K. Mitsuke, in the Proceed. ofPure and Applied Chemistry International Conference2010 (PACCON2010), Thailand, PTC-PO-45.
[2] B. P. Kafle, H. Katayanagi, K. Mitsuke, AIP Conf.
Proc. 879 (2007) 1809.
[3] D. A. Dahl, SIMION 3D ver. 7.0, Boise Idaho,
Scientific Instrument Services Inc., 2000.

45

BL3U

Performance of a High-Precision Transmission Grating with 5555-lines/mm
Groove Density for High-Resolution Soft X-Ray Emission Spectroscopy
H. Yamane1, T. Hatsui2 and N. Kosugi1
Institute for Molecular Science, Okazaki 444-8585, Japan
2
XFEL Project Head Office, RIKEN & JST-PREST, Hyogo 679-5148, Japan
1

The X-ray emission spectroscopy (XES) measures
X-rays emitted as a photon-in/photon-out process of
the inner-shell excitation. The XES technique
combined with the synchrotron radiation is a
powerful method to investigate element-specificexcitations and occupied partial density of states ofgases, liquids, and solids under various conditions.
However, a serious problem in the conventional XES
using a grazing-incidence spectrometer based on the
Rowland circle mount is a rather low quantum
efficiency, arising from various factors, e.g., (i) the
low emission probability of ~0.1 % at the emission
point, (ii) the number of focusing elements foremitted X-rays (horizontal direction only), and (iii)the low acceptance angle and low quantum efficiency
at charge-coupling devices (CCD) detector with thegrazing-incidence geometry in the soft X-ray region.
Moreover, these factors significantly sacrifice theenergy resolution. Such problems are in generalsolved by the use of high brilliant X-ray beam of over
1012–1013 photons/s. In this case, however, one has totake care of radiation damage, in particular for soft
materials such as organic and biomolecular systems.
In order to overcome the above problems, recently,
we have developed a new type of soft X-ray emission
spectrometer using a transmission grating (TG) at
BL3U of the UVSOR facility [1]. The spectrometer
adopts a novel optical design with a Wolter type I
premirror, a free-standing TG, and a back-illuminated
CCD, which enables high efficiency (~ 1 spectrum/h
at 1011 photons/s) and high energy resolution. A selfstanding TG made of silicon carbide (SiC) with thegroove density of 6250 lines/mm (160 nm periods)
has been evaluated as a prototype TG by NTT-AT N.
However, as confirmed from the scanning electron
microscopy (SEM) image, shown in Fig. 1(a), there isa distortion of the slit structure due to the resolution
limit in the present electron-beam lithography method
during the fabrication of TG.
In FY2009, the new TG, which is focused on thestability and accuracy of the slit structure as shown in
Fig. 1(b), has been fabricated. In the new TG, the SiC
thickness is about 500 nm, the groove density is 5555
lines/mm (180 nm periods), and the size of the slit is
108 nm at the surface side and 64 nm at the backside
as shown in Fig. 1(c). The flatness of the TG surface
is identically deflected as confirmed by a ZYGO
method (not shown).
Figure 2 shows a test XES spectrum for a Si(111)
wafer, measured at an incident photon energy hȞin =100 eV with ǻEin = 28.5 meV. We have preliminary

observed a very sharp elastic peak in the Si L
resonant XES spectrum with the full-width at halfmaximum of about ǻEout = 35 meV, i.e., E/ǻEout ~3000, although the alignment of the new TG optics
has not yet completed as suggested by the tailstructure in the elastic peak, which should be fixed by
the further alignment.

(c)

900 nm

180 nm(b)
160 nm(a)

300 nm (supporting structure)

180 nm108 nmCross section

539 nm

SiC
SiN

64 nm

Si

Fig. 1. SEM image for the prototype TG (a) and new
TG (b) with the groove density of 6250 lines/mm(160 nm period) and 5555 lines/mm (180 nm period),
respectively. (c) Basic structure of the new TG.

99.6: Resonant XES

hvin = 100 eV'Ein = 28.5 meVTGS slit = 5 Pm
Binning 1×16
Exposure 30min

Fluorescence

CCD image / pixel

Intensity / arb. units

Si(111): Gaussian fit

WG = 35 meVElastic

99.8

100

100.2

100.4

Emission Energy / eV
Fig. 2. Si L resonant XES spectrum (hȞin = 100 eV)
for the Si(111) wafer obtained by using new TG withthe best fit curve using the Gaussian function with thelinewidth of 35 meV.

[1] T. Hatsui et al., J. Electron Spectrosc. Relat.
Phenom. 144-147 (2005) 1059.

46

BL5B

Quantum Detection Efficiency of CsI-Coated Microchannel Plates
Measured by Using Pure-Calibrated EUV Beam
G. Murakami, G. Ogawa, K. Yoshioka, H. Watanabe and I. Yoshikawa
Department of Earth and Planetary Science, Graduate School of Science,
The University of Tokyo, Tokyo 113-0033, Japan(without CsI). The QDEs are calculated by the rate of
the MCPs count to the electron yield of the photo
diode which is absolutely calibrated. Table 1 shows
the result of the measurement. It shows that the QDE
of CsI is higher than that of bare MCP by 1.2 at 30.4
nm and 1.5 at 58.4 nm respectively.
For the next step, in addition to the 30.4nm and58.4 nm lines, we plan to measure the QDE at the83.4 nm line. Then the purity of 83.4 nm line isessential, and must be investigated for the next
machine time.

Introduction
We study to optically observe the Earth’s
plasmasphere, which is filled with cold plasmas(mainly H+, He+, O+ and electrons). The He+ andO+ ions have resonance scattering emission lines inthe extreme ultraviolet (EUV) region, at 30.4 nm(HeII) and 83.4 nm (OII) respectively. The intensityof each emission is proportional to column density ofeach scattered particle under the assumption of the
optically thin condition.
Microchannel plate (MCP) detection systems havebeen widely used in a variety of laboratory and space
applications to detect EUV radiations. EUVI
(Extremity Ultra-Violet Imager) for the ISS-IMAP
mission (Ionosphere, Mesosphere, upper Atmosphereand Plasmasphere mapping onboard the International
Space Station) is under development. The instruments
consist of band-pass filters and MCP detectors. The
top MCP surface is covered with cesium iodide (CsI)
photocathode in order to enhance the quantum
detection efficiencies (QDEs).
It is very important to get the absolute efficiency of
the instrument in order to grasp the plasma density
properly. In this experiment, we measure the QDE of
the MCPs which we use as a standard detector in ourlaboratory and evaluate the effect of CsI on the QDE.
Measurement and Result
We install an Al/Mg/Al (744Å/3958Å/747Å) filter
and an Sn (1730Å) filter on the entrance of the SOR
beam to eliminate the multi-order lines from 30.4nm
and 58.4 nm lines, respectively. At first, weinvestigate the purity of each line through theentrance filter. We judge the purity from theconsistency between the wavelength characteristics ofan Al/Mg/Al sample filter for the continuous lines at
UVSOR and those for the particular lines at the EUV
facilities of Institute of Space and Astronautical
Science (ISAS). The latter is measured for theemission lines of the helium gas with the discharge
light source. Fig. 1 shows the transmittances of thesample filter measured at UVSOR and at ISAS. The
Al/Mg/Al filter and the Sn filter are used as theentrance filter at UVSOR for 30.4 nm (Fig. 1a) and58.4 nm (Fig. 1b), respectively. It is clear that bothtransmittances of the filter are consistent at 30.4 nm
and 58.4 nm. We interpret from the result that thepure 30.4nm and 58.4 nm lines can be introduced
through each entrance filter by using PGM35.
With the available pure lines, then we measure the
QDEs of the MCP detector. The half area of the top
MCP is covered with CsI and the other area is bareFig. 1. The transmittances of the Al/Mg/Al sample
filter measured at UVSOR and at ISAS. The Al/Mg/Alfilter and the Sn filter are used as the entrance filter at
UVSOR for (a) 30.4 nm and (b) 58.4 nm, respectively.
Table 1. QDEs of the MCP detector
30.4 nm58.4 nmBare
3.45r0.06%
13.04r1.71%
CsI
4.13r0.07%
19.41r2.24%

47

BL6U

Construction of a New Experimental Setup with a High-Resolution
Electron Spectrometer for Gas Phase Spectroscopy on BL6U
E. Shigemasa, E. Nakamura, N. Kondo and T. Horigome
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
autoionizing electrons from atoms and molecules
have been measured, since their peak widths are
determined by the lifetimes, which are independent
on the photon energy resolution. One example ofthe spectra obtained is given in Fig. 2, whichcorresponds to the autoionization peaks from Ar+*
populated by the recapture of the 2p photoelectronfrom Ar due to the near threshold ionization. The
narrowest peak width observed is about 4 meV(FWHM) including the Doppler broadening of ~2.9
meV, which indicates the high performance of thepresent experimental setup. The development ofsoftware to realize 2D electron spectroscopy is inpreparation.

A new project for constructing the undulator
beamline BL6U has been started since 2007. We
have decided to choose the entrance slit-lessconfiguration for the monochromator, as a result of
the successful installation of such a configuration to
BL7U. In order to cover a wide photon energy
region (30-500 eV) with one single grating, avariable-included-angle Monk-Gillieson mounting
has been selected. The practical construction of
BL6U has begun from the summer shutdown in 2008.
The first light through the monochromator has been
observed in December 2008 and then precise tuningsof the monochromator have been continued. It has
been confirmed through its performance tests that the
monochromator designed can cover the photon
energy ranging from 40 to 400 eV with the resolving
power higher than 5000 and the photon flux morethan 1011 photons/sec, when the storage ring is
operated in the top-up mode.
Parallel to the construction program of BL6U, theinstallation of a new electron spectrometer for gas
phase spectroscopy has been planned. It is wellknown that high-resolution electron spectroscopy is a
powerful tool to investigate electronic structures ofatoms and molecules, especially when high-resolution
electron spectra and their polarization dependences
are measured as a function of photon energy inhigh-resolution mode. The ability of this twodimensional (2D) electron spectroscopy has been
demonstrated in our recent work at SPring-8 [1],where a special attention is paid for detecting slow
electrons following core excitations. In order toapply high-resolution 2D electron spectroscopy to theinvestigation of the L-shell excitations of the second
row elements, a new experimental setup for BL6U
has been designed and constructed. As a highperformance hemispherical electron energy analyzer,
MBS-A1, developed by the MB Scientific AB
company, has been selected.
Figure 1 shows a photograph of the experimental
setup, which is roughly composed of a vacuum
chamber, a rotational mechanism, an MBS-A1
analyzer, a gas cell, and a double layer mu-metal
screen. The analyzer is rotatable around the photon
beam axis. The vacuum chamber and the rotational
mechanism have been designed at UVSOR, andfabricated by TOYAMA Co., Ltd.
The othercomponents of the experimental setup have been
designed by MBS, and all the components related to
MBS have been transported and assembled at
UVSOR in August 2009.
In order to check the performance of the analyzer,

Fig. 1. Photograph of a new experimental setup forgas phase electron spectroscopy at BL6U.
㩷

15000

Ar
2

-1

2p3/2 -> Hl (KE ~ 0 eV)41

3s 3p md (recapture)
10000

2

4

3s 3p

㩷

CountsAutoionization

5000

0
0.5

1.0

1.5

Kinetic Energy (eV)Fig. 2. Autoionization spectrum following the 2p
photoionization of Ar.
[1] T. Kaneyasu, Y. Hikosaka, P. Lablanquie, F.
Penent, L. Andric, G. Gamblin, J.H.D. Eland, Y.
Tamenori, T. Matsushita and E. Shigemasa, Phys. Rev.
Lett. 101 (2008) 183003.

48

BL6U

Development of a High-Resolution Angle-Resolved UV/SX
Photoemission Spectroscopy System for Solid Surface Study at BL6U
H. Yamane1, T. Horigome1, S. H. Kang2, M. Nagasaka1, H. W. Yeom2 and N. Kosugi1
1
Institute for Molecular Science, Okazaki 444-8585, Japan
2
CAWL, Yonsei University, Seoul 120-749, Korea

Recently, a new undulator beamline BL6U, which
covers the photon energy (hȞ) of 40–600 eV with theresolution power (E/ǻE) of 104 at 1011–1012 photons/s,
has been constructed. Beside the development of agaseous high-resolution photoemission spectroscopy
system at BL6U [1], we have developed a highresolution angle-resolved photoemission spectroscopy(ARPES) system for solid and surface study.
Our ARPES system consists of an analysis
chamber, sample preparation chamber, and load-lockchamber. In the analysis chamber, we have installed a(i) high- resolution angle/spatially-resolved electron
analyzer (A1ER-SES200), (ii) liquid-helium (LHe)flow cryostat (Janis ST-400 UHV) with a compact
5-axes manipulation system, and (iii) low-energy
electron diffraction optics with a micro-channel plate(OCI MCP-LEED). The MCP-LEED optics realizes
the significantly reduced sample current ( A Æ nA ~pA), and thereby, one can apply the LEED techniqueto soft materials such as organic thin films without
the radiation damage by electrons. Thus, thecombination of (i)–(iii) allows the high-precision
ARPES and photoelectron diffraction (PED)
experiments.
The A1ER-SES200 system (MBS A1 combinedwith the SCIENTA SES-200 hemispherical electron
analyzer) gives a very sharp Xe 5p3/2 peak with thefull-width at half-maximum of 4.6 meV at the passenergy (Ep) of 5 eV can be achieved (cf. 3.8 meV at
Ep = 1 eV). In the angle-resolved mode, the electron
acceptance angle (ș) is ±6–7°.
For the precise ARPES and PED experiments, wehave designed and constructed the compact LHe
5-axes manipulator (Fig. 2). An azimuthal rotation(I) is controlled by the motorized worm-&-wheel andbevel gears, which have allowance for the small
backlash and the small thermal expansion between
room and LHe temperature. The LHe temperature istransferred from the cryostat to samples via thecopper braids. At the present diameter of the copper
braids, the maximum I rotation is about ±50°, and thelowest temperature at the sample position is about
20–25 K. At this low temperature, the total energy
resolution (ǻEtot), which includes the broadening
factors from the analyzer, incident photon beam, andtemperature, is obtained to 9.9 meV at hȞ = 43.2 eV
and Ep = 5 eV for the common use, as confirmed
from the ARPES spectrum for the Fermi edge of anevaporated polycrystalline Au film (Fig. 3).
The scheduled ARPES/PED experiments at BL6U
are organic semiconductor films and interfaces, andadatoms (or small molecules) on metal surfaces.
Intensity / normalized

HeI UPS@L1Spat5

Xe 5p 3/2
'Etot

Ep
/ meV / eV

Intensity
×1.0

-20

6.0

10

×1.8

4.2

5

×25

3.8

1

-10

0

10

Relative Energy / meV

20

Fig. 1. Xe 5p3/2 peak obtained by using a Gammadata
VUV5000 He lamp and the A1ER-SES200 system at
Ep = 1, 5, and 10 eV.

LHe

Cu braids

Azimuthal
Rotation

Intensity / normalized

Fig. 2. Photo of the LHe 5-axes manipulator withouta front radiation shield and a sample-mounting puck.

20

Exit Slit = 50 Pm
A1 Slit = 0.2 mm
Ep = 5 eV

Au@T ~ 20 K

'Etot = 9.9 meV(hv = 43.2 eV)

10

0

-10

Binding Energy (vs.EF) / meV-20

Fig. 3. Fermi edge of Au film measured at Ep = 5 eV,
hȞ = 43.2 eV, and T ~ 20 K.
[1] E. Shigemasa et al., UVSOR Activity Report 37(2010) a separate page in this volume.

49

BL7B

Measurement of Grating Reflectivity and Ghost Image
Created by MgF2 Plate

R. Ishikawa1, 2 , D. Fujimura1, 3, K. Ueda1, 2, H. Watanabe4, T. Bando1, T. Kobiki1,
N. Narukage1, H. Hara1, R. Kano1 and S. Tsuneta1
1
Hinode Science Center, National Astronomical Observatory of JapanMitaka 181-8588,
Japan
2
Department of Astronomy, University of Tokyo, Bunkyo-ku 113-0033, Japan3
Department of Earth & Planetary Science, University of Tokyo, Bunkyo-ku, 113-0033, Japan
4
Kwasan and Hida Observatories, Kyoto University, Yamashina-ku 607-8417, JapanWe are developing instruments for Chromospheric
Lyman-Alpha SpectroPolarimeter (CLASP), which
will be on board NASA sounding rocket. With thisrocket experiment, we will explore the magnetism of
solar outer atmosphere (chromosphere and transition
region) with the Hanle effect in the Ly-alpha line at
121.6 nm.

in mind for the CLASP spectrograph design. Using
CCD, we took images of a main beam and a ghost
image produced by MgF2 plate with the thickness of
0.5 mm at 121.6 nm. The CCD was located aroundthe focus position of BL7B. It was found that theintensity ratio of the ghost to the main beam was 25%,
and the difference in the positions imaged on the
CCD was 2.2 mm (Fig. 2). This information will be
helpful for our design of CLASP.
Finally, we briefly report the properties of the beams
at BL7B with G2 grating which we noticed in our
measurement. (1) The beam size became larger invertical direction with widening slit width of G2
grating from 10 um to 500 um. (2) The 121.6 nm
beam in the 1st order was imaged on our CCD, i.e.,around the focus position of BL7B, 0.8 mm and 10
mm away in horizontal and vertical direction,
respectively, from the 0th order beam, when the slit
width was 10 um.

Measurement of grating reflectivity at 121.6 nm
The estimation of the grating reflectivity is critical forthe development of CLASP spectrograph, since thehigh throughput is required to achieve the highpolarization sensitivity of 0.1 – 0.3%. However, we
did not have any information about the gratingreflectivity at 121.6 nm. Hence we planned toactually measure the reflectivity of an existing gratingby ourselves as a reference.
We borrowed the Toroidal Varied Line Space (TVLS)
grating from NASA MSFC for the measurement.
The groove number and the applied coating(Al/MgF2) of this TVLS grating are the same as what
we plan to develop. Fig. 1 shows the test setup for our
measurement. We set the incident angle to 12qwhichis consistent with the designed one for CLASP, andmeasured the reflectivity at 121.6 nm for the vertical(aligned to rulings) and the horizontal (wavelength
dispersion) polarization. We had already developed abeam cleaner using UV radiation at BL7B, and wereable to make perfect linear polarization light in verticaland horizontal direction combined with MgF2
waveplate. Though this grating is not optimized for
Ly-alpha line, we found that its re ectivity was
17.5% and 14.4% in horizontal and verticalpolarization, respectively, and there was no
significant difference in the reflectivity between twopolarizations. These values are higher than what we
expected before. On the basis of the conservative
estimation of CLASP throughput with these values,
we confirmed that our instrument achieves the highpolarization sensitivity of 0.1-0.3 %. We note that the
CLASP gratings will be optimized for Ly-alpha, andwe will obtain higher throughput.

Fig 1. Setup of grating reflectivity measurement for
the vertical polarization.

Measurement of ghost image
The polarization beam splitter in CLASP is made of
MgF2 plate, and the reflection from its back surface
creates a ghost image. This issue also should be kept

Fig. 2. Main beam and ghost image induced by
MgF2 plate with the thickness of 0.5 mm at 121.6 nmwith the slit width of 300 um.

50

BL7B

Development of MgF2 Waveplate and Polarization Analyzer

H. Watanabe1, N. Narukage2, D. Fujimura2, K. Ueda2, R. Ishikawa2, T. Kobiki2 and T. Bando2
1
Kwasan and Hida observatories, Kyoto University, Kyoto 607-8417, Japan
2
National Astronomical Observatory of Japan, Mitaka 181-8588, JapanWe developed a half waveplate and a polarization
analyzer made of MgF2 for Lyman-alpha line (121.6nm) by means of UV radiation at BL7B with the G2
grating. This is the basic experiment for“Chromospheric Lyman-Alpha Spectro-Polarimeter(CLASP)” rocket, which is planned to be launched in
2013. CLASP rocket will measure the weak vector
magnetic field in the solar chromosphere using
Lyman-alpha wavelength. As the magnetic field in thesolar chromosphere is very weak, the signal isdominated by linear polarizations from the Hanle
effect [1]. Our method is to measure the linear
polarization by taking the spectra of two orthogonal
polarization states simultaneously with a rotating half
waveplate and two polarization analyzers (one of theanalyzers works as a beam splitter).
MgF2 is a transparent crystal for UV wavelength
above 110 nm, and has birefringency with one slow
axis (ne: extraordinary refractive index) and two fastaxes (no: ordinary refractive index). In order toevaluate the performance of MgF2 polarization
analyzer, we measured the reflection/transmission(R-T) ratio as a function of the incident angle for bothp-polarized (the electric vector parallel to the opticalsurface) and s-polarized (electric vector perpendicular
to the optical surface) light. The reflected beam at
Brewstar’s angle is almost purely polarized consistingof s-polarized component, and thus is useful as apolarization analyzer. By fitting the R-T ratios shownin Fig. 2 , we found that the the Brewstar’s angle of
MgF2 is 59o, and 121.6 nm beam at BL7B is 89%
linearly polarized in the horizontal direction. The
reflection ratio at Brewstar’s angle is 29.4% fors-polarized and 0.30% for p-polarized component.
As the retardation measurement needs highlylinearly polarized light source, we set a beam cleaner
at the entrance of the chamber. The beam cleaner ismade of one Aluminum plate and one MgF2 plateboth located at incident angle of 60o (~Brewstar’s
angle for MgF2), and makes perfect linear
polarization light in horizontal direction (see Fig. 2).
The half waveplate for Lyman-alpha is also madeof MgF2 by stacking two plates whose slow axes areperpendicular to each other and whose thicknesses
slightly differ from each other. The retardation of a
waveplate is proportional to the product of the
thickness difference and (ne-no). For developing ahalf waveplate, the accurate value of (ne-no) is
necessary. There are few early works which measured(ne-no) [2]. We measured the retardation of threekinds of waveplates with thickness differences of
7.03 um, 8.46 um, and 14.04 um. We deduced thevalue of (ne-no) is 0.0035 +/- 0.00018 at 121.6 andthe thickness difference for a Lyman-alpha half
waveplate is 17.18 um. We are developing the half
waveplate for Lyman-alpha line using this result. On
the basis of R-T ratio and retardation measurements,
we can derive the optical constants of MgF2 at 121.6
nm as no=1.63, k=1.0 x 10-6. We are going to submit
these results to the Journal of the Optical Society ofAmerica in 2010 (the title will be “Optical Constantof MgF2 Plate at Lyman-Alpha Wavelength for
CLASP Experiment”).

Fig. 1. Photo of our measurement system. The
position of the waveplate and MgF2 plate arecontrolled by the stepping motors.

Fig. 2. Result of reflection/transmission ratio
measurement.
[1] J. Trujillo Bueno and A. Asensio Ramos,
Astrophysical Journal 655 (2007) 642.
[2] P. Laporte et al., J. Opt. Soc. Am. 8 (1983) 1477.

51