Ⅲ-1

Accelerators andInstrumentsⅢ -1. Accelerators and Instruments

Light sources

Development of 90° Bend-Type Spin-Rotator for
Inverse Photoemission Spectroscopy
Y. Kajiura 1, T. Inagaki 1,3, N. Yamamoto 1,2, M. Hosaka 2, A. Mano 2,
Y. Takashima 1,2, T. Konomi 3 and M. Katoh 2,3
12

Graduate School of Engineering, Nagoya University, Nagoya, 464-8603
Nagoya University Synchrotron Radiation Research Center, Nagoya, 464-8603
3
UVSOR Facility, Institute for Molecular Science (IMS), Okazaki, 444-8585

Transmission type (NEA-GaAs) spin-polarized
electron sources, in which pump laser light is injectedfrom the backside of the photocathodes and thepolarized beam is extracted from the front side, havebeen developed. By using this type of photocathodes,
the high brightness of ~2×107 A.cm-2.sr-1 and the highpolarization of ~90% were achieved [1, 2].
At UVSOR, we are planning to apply this type ofphotocathodes to the Spin-resolved Inverse
Photoemission Spectroscopy. For this purpose, acompact spin rotator is needed. A spin rotator enables
us to obtain arbitrary direction of electron spin.
Furthermore, to suppress the degradation of beam
qualities, a compact (shorter length) electron transfer
system is essential. Therefore, we have designed andmanufactured a compact spin rotator combined with
the 90° bending function.
Arbitrary spin direction according to the beam
direction is obtained by applying magnetic andelectric forces simultaneously [3]. The designed spinrotator consists of in-situ spherical electrodes(curvature radius of 50mm and electric poles gap of5mm), and a C-type bending magnet. We havedesigned the electro and magnetic components basedon numerical calculations by using the Poisson code
(2D) and Radia code (3D) [4]. The beam trajectories
were also evaluated by using the GPT code.
From the electrode structure described above, thecurvature radius of 50 mm and magnetic pole gap of> 48 mm were required for the bending magnet.
Because the beam trajectories evaluated by using only
electric or magnetic field should be equal and thevacuum chamber should be placed in the space
between the magnet and the electrodes. In the simple
C-type magnet case, it is difficult to satisfy therequirement for beam curvature due to the fringing
field. Then we have employed two sets of return yoke
and shield pole for both inject and extract sides.
As the result of the design, the spin-rotator size was
decided 198mm x 175mm x 130 mm (W, D, H).
Based on the numerical designs, we manufactured thebending magnet and the vacuum chamber (Fig.1).
The magnetic coil parameters were decided in theconsideration of wire-heating and current accuracy.
The coil consists of 30-turns electric wires and theoperation current is calculated to be around 7A.

Ⅲ -1

Figure 2 shows the measurement field values and it
is found that the result can be reproduced thenumerical calculation values with sufficient accuracy.
The beam trajectories were also evaluated fromvarious designed fields. In the case that only themagnetic field is applied, which corresponds to theparallel spin direction mode, the maximum beam
discrepancy between obtained and ideal trajectories
was obtained and estimated to be + 1.04 mm.
Because the acceptable discrepancy for beam transfer
is ±1.8 mm, it is confirmed that the designed spinrotator has sufficient performance.
Beaminject-side
175mm
198mm
130mm
Beam
extract-side
Fig. 1. 3D analysis model and fabricated spin rotator

Calculation
Experiment

B (G)

110
90
70
50
30
10
-10

-80 -40 0 40 80 120
Position (mm)Fig. 2. Result of magnetic field measurement.

[1] N. Yamamoto, T. Nakanishi et al., J. Appl. Phys.
103 (2008) 064905.
[2] X. G. Jin, N. Yamamoto et al., Appl. Phys. Ex. 1(2008) 045002.
[3]Andersen W. H. J., J. Appl. Phys. 18 (1967)1573.
[4]RADIA_URL:“http://www.esrf.fr/machine/support/ids/Public/Codes/software.html”

33

Ⅲ -1. Accelerators and Instruments

Light sources

Development of Temporal Response Measurement System forTransmission-Type Spin Polarized Photocathodes
T. Inagaki1,2, N. Yamamoto1, Y. Kajiura1, T. Konomi2, Y. Okano3, M. Adachi4, X. G. Jin1,
M. Hosaka1, Y. Takashima1 and M. Katoh2
1

Nagoya University, Nagoya 464-8601, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
Laser Research Center for Molecular Science, Okazaki 444-8585, Japan
4
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan2

Ⅲ -1

We have developed transmission-type spinpolarized photocathodes with negative electron
affinity (NEA). The spin-polarized electron beam isessential for “International Linear Collider” and so on.
It is also expected to be applied for “Spin-resolved
Inverse Photoemission Spectroscopy” [1].
In order to measure the temporal response ofphotocathodes, we developed the electron pulse
length measurement system with 20 kV DC gun (Fig.
1). In this system by using an rf deflecting cavity, theelectron beam is kicked transversely according to therf phase position and the longitudinal pulse structure
is projected to the transverse plane. We have
employed the resonance mode of TM120. The
resonance frequency is 2614 MHz for the rf cavity
and the resonance frequency corresponds to themultiple of RF acceleration frequency of UVSOR
storage ring, so the laser can be synchronized withUVSOR accelerator is used for the pump laser [2].
Temporal response of the photocathodes is evaluatedby comparing the electron pulse structure and thepump laser pulse length. The pump laser pulses areprovided by a mode-locked Ti:sapphire oscillator. In
the present system by using a pulse stretcher, thepulse length of the pump laser can be selected in therange between 20 ps and 45 ps (Fig. 2).
In the process of the rf cavity manufacturing, wemeasured the induced magnetic properties on the
beam axis by bead perturbation method and it isconsistent with the designed value. After the
installation of the rf cavity to electron gun system, thebeam deflecting test was carried out and it is foundthat the maximum induced field was about 1.4 G with
the input rf power of 5 W. This field strength isconsistent with the designed value and enough for
deflecting the 20 keV electron beam.
Furthermore, we carried out the comprehensive testfor our developed system with the GaAsP
photocathode with thickness of 600 nm. To realize
the laser transmissibility, the photocathode wasfabricated on GaP substrate. As the results, 48.3 pselectron beam pulse is obtained with 40.5 ps laser
pulse. Then the temporal response of thisphotocathode is estimated to be about 7.8 ps and we
considered that this result is consistent in view of the
thickness of GaAsP active layer [3].

Finally, in near future we are planning to shorten
the pump laser to 1 ps by improving the pulse
stretcher and we will make systematic measurement
for the various transmission-type photocathodes.

Fig. 1. Measurement system of temporal response.

Fig. 2. Stretcher.
[1] N. Yamamoto, doctoral thesis, Nagoya University(2007).
[2] T. Niwa, master’s thesis, Nagoya University(2013).
[3] X. Jin, Institute for Advanced Research, Nagoya
University, Applied Physics Express 6 (2013) 015801,“High-Performance Spin-Polarized Photocathodes
Usinga
GaAs/GaAsPStrain-CompensatedSuperlattice”.

34

Ⅲ -1. Accelerators and Instruments

Light Sources

Study on Vacuum Ultraviolet Coherent Harmonic Generation Using
Relativistic Electron Beam and Laser

1

2

S. Sekita1, M. Hosaka2, N. Yamamoto1,2, Y. Takashima1,2,
K. Hayashi3, J. Yamazaki3, T. Konomi3 and M. Katoh3

Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
Nagoya University Synchrotron Radiation Research Center, Nagoya 464-8603, Japan
3
UVSOR, Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, JapanⅢ -1
At UVSOR-III, we are developing a coherent VUVlight source using coherent harmonic generation(CHG) technique. An optical klystron, consisting of
two Apple-II type undulators and an electro-magnetic
buncher, has been already installed in BL1U.
Recently, we installed a VUV spectrometer at the U1experimental end station and made a CHG
experiment. Figure 1 shows a schematic diagram ofthe measurement system including the spectrometerand figure 2 shows a photograph of the actual system.
In the experiment, we employ Ti:Sa laser with 800
nm wavelength and 100 fsec pulse width as a seed
light source and observe 3rd-CHG (266 nm) using thespectrometer. Figure 3 shows the measured CHG
spectrum.
The measured spectral width is 2.2 nm andassuming Fourier-transform-limited pulse the pulse
duration is 50 fs. The value is shorter than theincident laser pulse width. Measured CHG intensity is
30 times of the SR intensity (Fig. 4), however thevalue is weaker than that of the calculated one [1].
This suggests that the interaction with the laser takes
place not in the whole bunch but only limited
transverse region due to poor alignment between thelaser and the electron bunch. In the near future, weare going to install an improved laser alignment
system.

Fig. 2. Photograph of the measurement system.

Fig. 3. Observed 3rd-CHG spectrum compared withspontaneous synchrotron radiation.

Fig. 4. Observed CHG radiation intensity
Fig. 1. Schematic of the measurement system for the
CHG experiment.

[1] S. Sekita, Master’s Thesis, Nagoya University(2014).

35

Ⅲ -1. Accelerators and Instruments

Light Sources

Development of Deep Ultraviolet Pulse Compressor
for Coherent Harmonic Generation Experiments
1

H. Zen1, T. Konomi2,3 and M. Katoh2,3Institute of Advanced Energy, Kyoto University, Uji 611-0011, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
3
The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585, Japan2

Ⅲ -1

The Coherent Harmonic Generation (CHG) from
relativistic electron beam through the Free Electron
Laser (FEL) interaction with high power laser ispromising way to generate short pulse EUV coherent
radiation [1]. However, power saturation occurs when
the incident laser pulse is too strong and it limits thenumber of photon in a pulse [2]. In conventional laser,
Chirped Pulse Amplification (CPA) technique iscommonly used for avoiding damage or power
saturation and to obtain high output power. We
proposed utilization of CPA to CHG technique toovercome the saturation problem [3].
We are planning to make proof of principle
experiment at the wavelength of 266 nm, the 3rd
harmonics of Ti-sapphire laser. For the experiment,
we need a pulse duration measurement system and a
DUV pulse compressor.
In this fiscal year, we have constructed a DUVpulse compressor. The schematic diagram is shown in
Fig. 1. The pulse compressor consists of a DUVgrating, a periscope, 500-mm linear translation stage,a roof mirror and dielectric mirrors. The groupvelocity dispersion (i.e. compression factor) of thiscompressor can be controlled by changing theposition of roof mirror. Figure 2 shows thephotograph of the developed compressor. In thiscompressor, DUV laser pulse experiences four times
diffraction on the same grating.
In order to adjust the compressor and check theefficiency, DUV laser pulses (! = 266 nm) are
generated by 3rd harmonic generation of Ti-Sapphirelaser using 2nd and 3rd harmonic generation crystals.
After finishing the adjustment of compressor, theincident and transmitted DUV laser power were

measured by a power meter (PH10I-Si-USB). As theresult, the measured incident power was 470 µW andtransmitted power was 120 nW. The measured
efficiency or transmittance of the compressor was
2.6 ! 10-4 and calculated diffraction efficiency of thegrating was around 13%. The diffraction efficiency of
the grating measured in manufacturer at 300 nm andLittrow configuration was around 65%. The measured
diffraction efficiency was significantly lower thanthat. We are planning to make further investigation on
the polarization and incident angle dependence ofdiffraction efficiency to achieve higher transmission.

Grating
Power
Meter

Roof Mirror
Periscope

Linear Stage
Fig. 2. Photograph of the developed pulse compressor[1] R. Prazeres et al., Nucl. Inst. Meth. A 304 (1991)
72-76.
[2] T. Tanikawa et al., Appl. Phys. Exp. 3 (2010)2702.
[3] H. Zen et al., Proc. of FEL2011 (2012) 366-369.

Grating

N = 1800 g/mm
! B(Litt) = 300 nm(60 mm x 60 mm)

500 mm Linear Translation

Roof
MirrorFrom CHG-FEL (Lower Beam)
Periscope

To Pulse Duration Measurement (Higher Beam)

Fig. 1. Schematic drawing of pulse compressor.

36

Motorized
LinearStage

Ⅲ -1. Accelerators and Instruments

OthersPerformance Evaluation of New Type Nuclear Emulsion with Electron BeamK. Ozaki1, S. Aoki1, K. Kamada1, E. Shibayama1, S. Takahashi1, S. Tawa1, F. Mizutani1,
H. Kawahara2, H. Rokujo2 and GRAINE collaboration
1

Department of Human Environment Science, Kobe University, Kobe 657-8501, Japan
2
Graduate School of Science, Nagoya University, Nagoya, 464-8602, JapanWe are promoting GRAINE project [1], which isballoon-borne experiment to explore the gamma-ray
astrophysics with nuclear emulsion.
Nuclear emulsion is a 3-dimensional tracking
detector with 0.1 µm precise position resolution.
Nuclear emulsion records the track of silver grains
produced by trajectory of charged particle (see Fig. 1).
Self-production of new type emulsion has developedat Nagoya University since 2010. The performance
evaluation of new type emulsion is presented. This
work is mainly for next balloon experiment of
GRAINE in 2014, Australia.
In order to control / improve the sensitivity to thecharged particle, four types of emulsions which arechanged the amount of silver halide were developedat Nagoya University. Emulsion films were made bycoating emulsion on both side of plastic base. Thesefilms were exposed to electron beam at UVSOR toevaluate their sensitivity. After development the films,
the measurement of the numbers of silver grains wasdone with optical microscope.
Figure 2 shows the result of measurement of Grain
Density (GD: counts of silver grains per 100µm) for
four types of emulsions. Development time is 25
minutes for all types. There is good correlation
between GD and the amount of silver halide. GD ofconventional nuclear emulsion (OPERA film [2]) is
about 30, so we could succeed to improve thesensitivity by increasing the amount of silver halide.
While multiple coulomb scattering increases due tothe increasing the amount of silver halide, so there istrade-off.
It is also important to evaluate about characteristicof long-term preservation of new type emulsion film.
In the case of GRAINE, it takes about 6 months fromfilm production to balloon flight. This time we haveevaluated about the highest silver halide type ofemulsion. Films were exposed to electron beam at
UVSOR just after production, and 1, 2.4, 3.8, 4.9
months after production. Preservation environment isshielded place with lead block at room temperatureand humidity (about 14-20 degree and 40-60 %RH).
After development the films, the measurement of GD
was done with optical microscope.
Figure 3 shows the result of long-term preservationof new type emulsion film. Development time is 20
minutes mainly, but film of 3.8 months after is 25
minutes. Black and red circle means difference ofmeasurement person. GD is almost stable after
5months. There is no problem about characteristic oflong-term preservation to perform the GRAINE andother experiments.

Fig. 1. Microscopic view of emulsion recorded
charged track.

Fig. 2. The amount of silver halide dependence ofGrain Density.

Fig. 3. Characteristic of long-term preservation of
new type emulsion film.
[1] S. Aoki et al., <arXiv: 1202. 2529 [astro-ph.IM]>.
[2] T. Nakamura et al., Nucl. Instr. Meth. A 556(2006) 80.

37

Ⅲ -1

Ⅲ -1. Accelerators and Instruments

BL2B

Reconstruction of the Beamline BL2B for Development of Photoelectron
Spectroscopy for Organic Materials
S. Kera1, K. R. Koswattage1,2, K. Yonezawa1, J. P. Yang1, Y. Nakayama1, K. K. Okudaira1and H. Ishii1
1

2

Ⅲ -1

Graduate School of Advanced Integration Science, Chiba 263-8522, JapanUVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japanto the beamline and storage ring in case of accidents.
The safety interlocks at six vacuum valves of thebeam line are controlled by a system with vacuum
gauge readings. There is a touch-panel display andthe screen show a schematic drawing of the beamline
along with vacuum valve status. Further, two power
distribution units have been built for proper handlingthe electricity in the beam line.
A new end-station for the photoelectron
spectroscopy equipped with a hemispherical analyzer(SCIENTA R3000) and a liquid-He-cooled cryostat(temperature range of 15-400 K) with 5-axis stage istransferred from Chiba Univ. The experimental
chambers have been adjusted to place for thephoton-beam trajectory.

Electronic/optical devices based on π-conjugatedmolecular semiconductors have moved out of the
field of the academic curiosity and are now regarded
as valuable brilliant technologies as found for organic
field-effect transistors and organic photovoltaics etc.
However the fundamental pictures of the intrinsic
electronic and optical properties are often hindered by
the presence of chemical and physical imperfections,eg. chemical impurities, energetic and structural
disorder. Thus, the development in the surface science
technique and the availability of research stations at
synchrotron facility suited for characterizing the wide
range of molecular materials is desired for achieving
the fundamental understanding.
The bending-magnet beamline of BL2B isdeveloped by Prof. Mitsuke et al.[1,2], where the18-m spherical grating monochromator (Dragon type)with three gratings (G1 – G3) and four mirrors (M1 –M4) to achieve a high-resolution and photon flux andhad been used for gas-phase experiments. The
monochromator can cover the energy range of 23-205
eV, a resolving power of 2,000-8,000 and photon fluxof more than 1010 photons/s[2].
We started the reconstruction of the beamline forphotoelectron spectroscopy of molecular solids in
September 2013. In the monochromator, it isnecessary to insert two plane mirrors M2 and M3
across the photon-beam between G3 grating and S2
slit in order to get precious light from G3 grating.
These mirrors should be removed from the optical
path when G1 or G2 grating is employed. However,there was a problem of the linear motion of the mirror
system due to a deformation of a vacuum rod in
between mirror and motor system. A new vacuum rod
has been replaced (TOYAMA) in order to solve themalfunction of the M2 and M3 mirror system.
A UHV chamber so called monitoring chamber has
been placed downstream of the refocusing mirror
chamber. The monitoring chamber contains threelinear motion feedthroughs, where a silicon
photodiode for absolute photon flux measurement(AXUV-100, IRD), a sapphire plate to monitor thephoton-beam position, a Au mesh of the size 100 tomonitor the relative photon flux and for the beamlinealignment. The third feedthrough is to equip thefilters to attenuate higher order light and, at thepresent foil structure of Al/Mg/Al filter (LUXEL) is
attached. The same chamber can be also employed forgold evaporation.
A new interlock system has been introduced toensure the safety of users as well as prevent damage

Fig. 1. (top) BL2B equipped with an 18-m SGM.
Two optical paths with including angles of 160° forG1 and G2 and 140° for G3 are indicated. S2: exit
slit; Q: sample point (after ref [1]). (bottom)
Schematic layout of BL2B.
[1] H. Yoshida and K. Mitsuke, J. Synch. Rad. 5(1998) 774.
[2] M. Ono, H. Yoshida and K. Mitsuke, Nucl.
Instrum. Meth. Phys. Res. A 467-468 (2001) 577.

38

Ⅲ -1. Accelerators and Instruments

BL3B

Observation of VUV Emission from Al2O3 and Nd:LaF3 Crystals
M. Kitaura1, S. Kurosawa2,3, J. Pejchal2, K. Fukui4, K. Nakagawa5, S. Watanabe6,
A. Ohnishi1, K. Ogasawara6, M. Hasumoto7 and M. Sakai7
1

Department of Physics, Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
2
Institute for Materials Research, Tohoku University, Sendai 980-8679, Japan3
New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8679, Japan
4
Department of Electrical and Electronics Engineering, University of Fukui, Fukui 910-8507, Japan
5
Graduate School of Human Development and Environment, Kobe University, Kobe 657-8501, Japan
6
School of Science and Technology, Kuwansei University, Sanda 669-1337, Japan
7
UVSOR facility, Institute for Molecular Science, Okazaki 444-8585, Japan
Since 2011, the BL3B beamline offfers many
researchers for the opportunity of spectroscopy
experiment using VIS, UV and VUV photons tomany researcher [1]. One of the next targets is toextent observable emission range to higher-energy
side. Few VUV emission spectroscopic experiments
have been performed in synchrotron radiation
facilities. The SUPERLUMI station at HASYLAB in
DESY was the only experimental setup for VUVemission spectroscopy; however, it still remains
closed at present. We have installed the spectroscopy
system consisting of two MgF2 lenses, a CCD
detector (Princeton Instruments SX-100B) and a
monochromator (Acton VM-502) at the BL3B. To
check whether this system works, we have measured
VUV emission and excitation spectra of Al2O3 andNd3+-doped LaF3 (Nd:LaF3) crystals at 9 K. These
crystals have been known to show VUV emission at
low temperatures [2, 3].
Figure 1 shows the emission and excitation spectraof pure Al2O3 crystals. Blue squares clearly show thatan emission band appears around 7.51 eV under
excitation at 8.92 eV. This band is excited in thefundamental absorption band of Al2O3. These data arein agreement with those published previously [2],where the 7.51 eV band was attributed to the radiativeannihilation of self-trapped excitons (STEs).
Emission and excitation spectra of Nd:LaF3 crystals
are shown in Fig. 2. As indicated by blue squares, asharp emission peak is observed around 7.08 eV
under excitation at 7.75 eV. The 7.08 eV band is
excited in the 4f!5d absorption region of Nd3+ ions(red squares). This feature suggests that the 7.08 eVband is assigned to the 5d!4f transition of Nd3+ ions.
The observed spectra are almost the same as those in
Ref [3]. Another band is seen around 5.74 eV, also
being assigned to the 5d!4f transition of Nd3+ ions.
We will install a focus mirror system the nex year
to collect VUV emission more efficiently next year.
This is vital for the detection of VUV emission,
because the sensitivity of the detector such as PMT
and CCD is relatively low in the VUV range.
Furthermore, the experimental setup for the timeresolved emission and excitation spectroscopy in thewide energy range from VIS to VUV will be also

installed for the investigation of photo-excited state
dynamics in crystalline solids.

Fig. 1. Emission (blue) and excitation spectra (red)for the Al2O3 crystal. The emission and excitation
spectra were measured at 9K for 8.92 eV excitation
and 7.51 eV emission.

Fig. 2. Emission (blue) and excitation spectra (red)for the Nd3+-doped LaF3 crystal. The emission andexcitation spectra were measured at 9K for 7.75 eV
excitation and 7.08 eV emission.
[1] K. Fukui et al., J. Synchrotron Rad. 21 (2014)452.
[2] V. V. Harutunyan et al., Eur. Phys. J. B 12 (1999)
35.
[3] P. Dorenbos et al., J. Lumin 69 (1996) 229.

39

Ⅲ -1

Ⅲ -1. Accelerators and Instruments

BL7B

Stokes Parameters Measured by VUV Spectral Ellipsometer
1

Faculty of Engineering, Tohoku Inst. Tech., Sendai 982-8577, Japan
2
Faculty of Engineering, Univ. of Fukui, Fukui 910-8507, Japan

Ellipsometers are known as powerful tools todetermine optical properties such as opticalconstants of thin films or bulk materials [1]. For
typical ellipsometers, the photon beam entering thesample should be highly polarized or its polarization
state should be characterized. Contrary to typicalellipsometers, the one developed [2] is capable todetermine the photon source Stokes parameters aswell as the sample optical constants.
Figure 1 shows a schematic structure of the VUVellipsometer. Monochromatic radiation hits a sample
specimen at an angle of incidence of 67.5 or 45.
The reflected beam is detected with an inclined
photodiode with an angle of incidence of about 40.
The ellipsometer chamber can be rotated around theaxis of the incidence with angle ! using a rotational
feedthrough with magnetic sealing fluid. The analyzer
unit can also be rotated around the reflected beamfrom a sample with angle ". Intensity measurementsin the several combinations of ! and " make itpossible to analytically solve all the unknown
parameters, that is, the Stokes parameters of theincident radiation, optical constants of the sample anddetector polarization characteristics of the detector.
We used the ellipsometer at the normal incidence
monochromator beamline, BL7B at UVSOR for threesample mirrors, Au, AlN and AlN photodiode.
Complex refractive indices of AlN obtained were
published elsewhere [3-4]. Figure 2 shows Stokes
parameters obtained for the radiation emerging from
BL7B. Note that measurements were repeated threetimes for each sample incidence angles of 45˚ and
67.5˚ by changing the sample mirrors. Although thedata of S2 and S3 are somehow scattered, the data of
S1 shows better reproducibility independent of thesample mirror.
Considering the rather large vertical accepting
angle, the results obtained are considered to bereasonable. It should be also mentioned that thepolarization, in principle, could be different
depending on the electron beam condition such as
beam position and beam emittance in the storage ring.
Although we were not able to attribute the cause of
the scatter of S2 and S3, it can be probable that theelectron beam instability of the storage ring and/or
difference in illuminating condition in the beamline
optics is partly responsible for it since we observed
rather big changes in Stokes parameters over manytimes measurements.

photon
beam

!
67.5°
40°

"

Fig. 1. Schematic layout of the ellipsometer.


1.00

Stokes parameters

0.75
0.50
0.25
0.00
-0.25

(a) 45°

-0.50
-0.75

S1(Au)
S2(Au)
S3(Au)

S1(AlN)
S2(AlN)
S3(AlN)

S1(AlN PD)
S2(AlN PD)
S3(AlN PD)

-1.00
1.00

0.75

Stokes parameters

Ⅲ -1

T. Saito1, K. Ozaki2 and K. Fukui2

0.50
0.25
0.00
-0.25
-0.50

(b) 67.5°

-0.75
-1.00

5

10

15

20

25

Photon energy [eV]Fig. 2. Stokes parameters obtained by the ellipsometerusing 3 different samples. The angle of incidence tothe sample: (a) 45˚ and (b) 67.5˚.
[1] D. E. Aspnes, in: E. D. Palik (Ed.), Handbook of
Optical Constants of Solids (Academic Press, Boston,1985).
[2] T. Saito, M. Yuri and H. Onuki, Rev. Sci. Instrum.
66 (1995) 1570.
[3] K. Ozaki et al., UVSOR Activity Report 38(2010) 105.
[4] T. Saito et al., Thin Solid Films, available online
12 March 2014
( http://dx.doi.org/10.1016/j.tsf.2014.02.099 ).

40

Ⅲ -1. Accelerators and Instruments

BL7B

Efficiency Measurement of a Holographic Concave Grating
for VUV Solar Spectro-Polarimetry
H. Hara1,2, M. Kasuga2, T. Kobiki1, K. Miyagawa2 and N. Narukage3
1

National Astronomical Observatory of Japan, Mitaka 181-8588, Japan
Department of Astronomy, School of Science, The University of Tokyo,
Tokyo, 113-0033 Japan
3
Institute of Space and Astronautical Science, JAXA, Sagamihara, 252-5210, Japan2

Ⅲ -1
We are developing a payload of a sounding rocket
experiment named the Chromospheric Lyman-Alpha
Spectro-Polarimeter (CLASP) [1] (Fig. 1). CLASP is
an instrument to detect low-level polarization signals
with an order of 0.1% photometric sensitivity in the H
Lyman-alpha line at 121.6 nm for the measurement ofmagnetic fields in the upper chromosphere andtransition region of the Sun. A holographic-ruled
spherical concave grating of 110 mm diameter with a
3000 gr/mm groove density is used in the
spectro-polarimeter that requires a high efficiency(>0.18). The grating for the experiment was
fabricated by Horiba Jobin Yvon (HJY), which has
rich heritages for providing the flight gratings in thespace programs.
In parallel with developing the flight optics, wehave been developing the grating for the future use inspace astronomy with domestic companies. One ofthe programs is to make a high-efficiency holographic
concave grating in collaboration with Shimadzu
Corporation. The grating specification is almost thesame as that of the CLASP flight grating. It has aspherical concave surface of 110mm effective areawith groove density of 3,000 gr/mm and a rectangulargroove shape reshaped by the ion-beam etchingprocess. Three gratings fabricated this time are mastergratings. The grating substrate is fused silica, while
Zerodur is used for the CLASP replica gratings.
Al/MgF2 is coated on the grating surface to enhancethe diffraction efficiency.
Figure 3 shows the absolute grating efficiency of
one of three gratings measured at the beam line BL7B.
Although non-uniformity in efficiency is found overthe effective grating aperture, the efficiency is goodenough for the specification for the CLASP grating,and is comparable to the CLASP flight gratings thathave been fabricated by HJY. The reflectance of thewitness sample mirror coated by Al/MgF2 with theconcave grating is 0.75 at 121nm, so that the 30!40%
groove efficiency has been achieved. Other two
gratings have also shown good absolute efficiency of
0.24-0.28 with better uniformity over the grating
surface, though they partially have areas with low
efficiency of 0.05 due to the local failure of groove
formation.
This work was supported by a Grant-in-Aid for
Scientific Research (B) (No. 23340052) from the

Ministry of Education, Culture, Sports, Science andTechnology of Japan.

Fig. 1. Concave grating in the CLASP polarimeter.

Fig. 2. (left) Holographic spherical concave grating
fabricated by Shimadzu Corporation and (right) its
groove profile.

Fig. 3. Absolute grating efficiency of the holographic
concave grating measured at 121nm in red characters.
[1] R. Kano et al., SPIE 8443 (2012) 84434F.

41

Ⅲ -1. Accelerators and Instruments

BL7B

Performance Verification of Flight Filter Unit for CLASP Slit-Jaw System
M. Kubo1, N. Narukage1, G. Giono2, R. Ishikawa1, S. Ishikawa1, K. Aoki3, T. Kobiki1,
Y. Suematsu1, T. Bando1 and R. Kano1
12

National Astronomical Observatory of Japan, Tokyo 181-8588, Japan
Department of Astronomical Science, Graduate University for Advanced Studies (SOKENDAI), Tokyo 181-8585,
Japan
3
Department of Astronomy, University of Tokyo, Tokyo 113-0033, Japan

Ⅲ -1
CLASP is a sounding rocket program, for the firsttime, to detect the linear polarization signal in Lyman
alpha (121.567nm) emitted from the upper
chromosphere or transition region of the Sun [1]. The
telescope of CLASP focuses a solar image on a slit,
and the light passing through the slit feeds into thespectropolarimeter that measures the spectra of thelinear polarization. The outside of the slit has a mirror
surface, and the solar image outside the slit isreflected to the slit-jaw system. The slit-jaw system
will obtain Ly-alpha images by focusing optics with apair of Ly-alpha narrow band filters. The images areused to select the instrument pointing during flightand to help the interpretation of the data obtained by
the spectropolarimeter.
A filer unit (Fig.1) of the slit-jaw system holds apair of Ly-alpha filters. The Ly-alpha filters aredeveloped by the Acton Optics & Coatings. The
diameter of the filter is one inch and its thickness is
2.5mm. The filter unit is fabricated by the Genesia
Corporation. Their designs are based on
measurements of prototype of Ly-alpha filters in
FY2011 [2].
The transmissivity in Ly-alpha and the visible light
rejection performance of the Ly-alpha filters areimportant for obtaining Ly-alpha images because theamount of photons in the visible light is much higher
than photons in Ly-alpha wavelength. Figure 2 shows
the transmissivity of a witness sample that is coatedsimultaneously with the flight Ly-alpha filters. The
transmissivity is 10% in the Ly-alpha wavelength andless than 10-3 % for the visible light. The measured
transmissivity satisfies our requirements, and then thevisible light contamination is less than 1% in the
Ly-alpha images. We conclude that the flight
Ly-alpha filters are successfully fabricated.
A pair of Ly-alpha filters is mounted at the angle ofincidence (AOI) of 0 degree, and the coated surfacesof the two filters face each other at a distance of 5mm.
The ghost images are created by the reflection on theback and coated surfaces of a filter, and by thereflection between two filters. The Ly-alpha images
though the flight filter unit are taken by CCD camera
at AOI = 0 and AOI=10 degrees (Fig.3). We haveconfirmed no issue of the ghost images created by thefilter unit: (1) the intensity of ghost beams to the main
beam is less 1%, (2) the distance between the ghost
beam and main beam is expected value (about 1.7mm

in the case of AOI=10 degree), and (3) there is no
unexpected ghost pattern.

Fig. 1. Photo of the CLASP filter unit.

Fig. 2. Transmissivity of the Ly-alpha filter (red line).

Main beam

1st ghostFig. 3. Left: Main beam and ghost beam image
created by the filter unit at the AOI of 10 degree.
Right: Intensity along the dashed red line in the left
panel.
[1] R. Kano et al., SPIE 8443 (2012) 84434F.
[2] M. Kubo et al., UVSOR Activity Report 39(2011) 43.

42

Ⅲ -1. Accelerators and Instruments

BL7B

Waveplate Axis Alignment for the CLASP Sounding Rocket
S. Ishikawa1, G. Giono2, R. Ishikawa1, N. Narukage1, R. Kano1 and T. Bando112National Astronomical Observatory of Japan, Tokyo 181-8588, Japan
Department of Astronomical Science, Graduate University for Advanced Studies (SOKENDAI), Tokyo 181-8585,
Japan

The
Chromospheric
Lyman-Alpha
SpectroPolarimeter (CLASP) is a sounding rocket
experiment to observe the linear polarization profileof the Lyman-alpha line (vacuum ultraviolet, 121.6nm) from the Sun for the magnetic field measurementin the upper chromosphere and transition region [1].
CLASP uses a continuously rotating MgF2 halfwaveplate [2] and reflecting polarization analyzer tomeasure the Lyman-alpha linear polarization. A
digital signal to trigger the CCD camera exposure issent out from the motor every 22.5-degree rotation of
the waveplate to drive the linear polarization degree
and angle.
To measure the polarization angle
precisely, it is necessary to align the waveplate on the
motor with a small angle uncertainty. The estimatedpolarization angle uncertainty from the CCD photon
noise is 0.8-degree, and the goal was to align the
waveplate with respect to the motor with better than
0.8-degree. Before this alignment experiment, thewaveplate angle is adjusted just by looking at areference marking-off on the waveplate edge by eye,and the uncertainty is not smaller than a few degrees.
We measured the relative angle between the
waveplate and motor with the UVSOR BL7B beamwith the wavelength of the Lyman-alpha light, andadjusted the waveplate angle. The experimental
setup is shown in Fig. 1 and Fig. 2. We made thelinearly polarized Lyman-alpha beam by the UVSOR
beam with a reflecting polarization analyzer. The
polarized beam is going through the rotating
waveplate, and the polarization direction changes
continuously. The linear polarization component
parallel to the certain direction is extracted by thereflecting polarization analyzer and a time profile ofthe intensity of the extracted component is recorded
by a photodiode. The recorded time profile, whichis called the polarization modulation, and theexposure synchronization signal are recorded
simultaneously. The rotation speed of the motor is
4.8 seconds per one rotation; therefore we measured
the signals with the high sampling frequency of 1
kHz to estimate the waveplate angle with the better
precision than 0.1-degree (one sampling interval of 1
ms corresponds to 0.075-degree).
We estimated the deviation angle of the waveplatewith respect to the motor to be 0.66-degree from theobtained polarization modulation (shown in Fig. 3).
We adjusted the waveplate angle to cancel thedeviation. After the adjustment, we measured thepolarization
modulation
andtheexposure

synchronization signal again, and the deviation was~0.05-degree. Therefore, we confirmed that the
waveplate angle is successfully aligned and theremained deviation was much less than therequirement.
PhotodiodeHi-R
MirrorWaveplate +Mounting
Jig

Motor
MgF2

BL7B
beam

Hi-R
analyzer

MgF2

Fig. 1. Overview of the experimental setup.

           

Fig. 2. Photo of the experimental setup.

Fig. 3. Obtained polarization modulation. Only apart (10 seconds, ~2 waveplate rotation) of theobtained data is plotted.
[1] R. Kano et al., SPIE 8443 (2012) 84434F.
[2] R. Ishikawa et al., Appl. Optics. 52 (2013) 8205.

43

Ⅲ -1

Ⅲ -1. Accelerators and Instruments

BL7B

Development of Mechanically Ruled Grating for the VUV Application
R. Ishikawa1, S. Ishikawa1, R. Kano1, T. Bando1, M. Koyama2,
Y. Enokida2, T. Sukegawa3 and S. Tsuneta4
1

National Astronomical Observatory of Japan, Mitaka, 181-8588, Japan
Corporate Production Engineering Headquarters, CANON Inc., Kawasaki, 212-8602, Japan
3
Corporate R&D Headquarters, CANON Inc., Utsunomiya, 321-3292, Japan
4
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, 252-5210,
Japan
2

Ⅲ -1

The measured reflectivity of the NiP plane mirror
from 115 to 300 nm allows us to evaluate the opticalconstant of NiP and simulate the diffraction
efficiency of the NiP grating. We found that the 0thorder reflectivity and diffraction efficiency at +/-1storders are consistent with the simulation results withthe groove depth of 45 nm, and the groove depth of
28 nm gives us the well-balanced diffraction
efficiency between TE and TM. We also found thatthe simulation depends strongly on the opticalconstant of the material, and the evaluation isnecessary for the development of the grating.
The relative diffraction efficiency of our sample islarge and reproduced by the simulation. The
difference in efficiency between TE and TM, whichshould be avoided in the polarization measurement,
can be suppressed by optimizing the groove depth.
Thus, we conclude that the first step of thedevelopment of mechanically ruled gratings was
successfully done. Next step is to develop the coating
to enhance the absolute diffraction efficiency.

For the vacuum-ultraviolet (VUV; λ < 200nm)
applications, holographic gratings have been widelyused, but here we focus on the capability of amechanically ruled grating, since it is flexible inchoice of groove density and surface figure comparedwith the holographic grating. As a first step of thedevelopment of a mechanically ruled VUV grating,
we have fabricated a test sample made of NiP withthe groove density of 5000 lines/mm and the effective
area of 10 mm x 10 mm, and evaluated theperformance at the UVSOR BL7B. Since we consider
the possibility to apply this grating to the CLASP
sounding rocket experiment [1] in the future, which
intends to measure linear polarization at the hydrogen
Lyman-! line (121.6 nm), our experiment was donewith a focus on this wavelength. For the reference,
we have also performed the measurement of the NiPplane mirror made by cutting work.
Figure 1 shows the photograph of the surface shapeof the grating sample observed with the Atomic ForceMicroscope (AFM), and the micro-roughness isfound to be very good with 0.6 nm RMS, indicating
very low stray light. Figure 2 represents thereflectivity of 0th order with the angle of incidence(AOI) of 5 deg for TE (electric vector is parallel tothe groove) and TM (electric vector is perpendicular
to the groove). We found significant difference in thereflectivity between two incident polarization states;
the reflectivity for TM is lower than that for TE, andthe difference becomes larger at longer wavelength(λ>120 nm). At the wavelengths of 183 nm and 217
nm (shown with dotted lines in Fig. 2), the TM
reflectivity represents the local maximum, and thesewavelengths correspond to the wavelengths, where+1st and -1st orders disappear for the grating withgroove density of 5000 lines/mm at AOI=5deg. The
diffraction efficiency of +1st and -1st orders at 121.6
nm is found to be 6.4% and 7.8% for TM and 11.0%
and 12.1% for TE. The similarity in the reflectivity
among +1st and -1st orders indicates that the groove
shape is symmetrical, while the higher efficiency for
TE indicates that the groove depth is not optimizedfor 121.6 nm (see next paragraph for more detail).
We also find that the reflectivity of plane mirror
sample at AOI=5deg is 28% at 121.6 nm. Thus, therelative diffraction efficiency of our grating sample isestimated to be 22 - 43%.

Fig. 1. Photo of grating surface.

Fig. 2. Reflectivity of NiP grating sample at 0th orderwith AOI=5 deg for TE and TM.
[1] R. Kano et al., SPIE 8443 (2012) 84434F.

44Ⅲ -1. Accelerators and Instruments

BL7B

Birefringence of MgF2 in the Vacuum Ultraviolet and Development of an
MgF2 Half-Waveplate
R. Ishikawa1, R. Kano1, T. Bando1, Y. Suematsu1, S. Ishikawa1, Y. Katsukawa1, M. Kubo1, N.
Narukage1, H. Hara1, S. Tsuneta2, H. Watanabe3, K. Ichimoto4, K. Aoki5 and K. Miyagawa5
1

2

National Astronomical Observatory of Japan, Mitaka, 181-8588, Japan
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, 252-5210,
Japan
3
Unit of Synergetic Studies for Space, Kyoto University, Kyoto 607-8417, Japan
4
Kwasan and Hida Observatories, Kyoto University, Takayama 506-1314, Japan
5
Department of Astronomy, School of Science, The University of Tokyo, Tokyo 113-0033, Japan

Figure 2 shows the birefringence of MgF2 as afunction of wavelength, derived from the phaseretardation measurement of the waveplate sample
with d1 - d2 = 15.755 µm. We found that ne − no =0.004189 ± 0.000039 at 121.57 nm. Based on thisbirefringence, we fabricated the flight waveplate with
d1 - d2 = 14.51 µm, and measured the phaseretardation to be 2π at the BL7B. Thus, we conclude
that we successfully completed the development of ahalf-waveplate for the CLASP experiment.

Spectro-polarimeteric observations in the vacuumultraviolet (VUV) region are expected to be
developed as a new astrophysics diagnostic tool forinvestigating space plasmas with temperatures of>104 K. A team of researchers from Japan, the USA,
Spain, France, and Norway has been developing thehigh-throughput chromospheric Lyman-alpha spectropolarimeter (CLASP), which is aiming to measure thelinear polarization of the hydrogen Lyman-α line (λ =121.567 nm) for the first time [1]. Precise
measurements of the difference in the extraordinary
and ordinary refractive indices are required fordeveloping accurate polarimeters, but reliable
information on the birefringence in the VUV range isdifficult to obtain. We have measured thebirefringence of magnesium fluoride (MgF2) around121.57 nm at the BL7B beamline using prototype of
MgF2 waveplates, and developed a flight halfwaveplate for the CLASP rocket experiment. Our
waveplates consist of two stacked MgF2 plates withslightly different thicknesses and their principal axes
are rotated by 90° with respect to each other.
A schematic of our experimental setup is shown in
Fig. 1. We employed three MgF2 plates set at
Brewster’s angle (59°). Using two MgF2 plates,
linearly polarized light in the horizontal direction
with a polarization degree of >99.999% was directed
onto a waveplate sample. With this configuration, we
measured the intensities Iobs at φ=0° and φ=45° (φ isthe angle of the principle axis of a waveplate from thehorizontal direction), and calculated the ratio which isafunctionofphase
retardationδ,A(λ)=Iobs(φ=45°)/Iobs(φ=0°)=[(1+PER)+(1-PER)cosδ(λ)]/2. The polarization extinction ratio (PER) is theratio of the p-polarization reflectivity to thes-polarization reflectivity. From the amplitude A(λ),
we determined δ as a function of wavelength and thenderive the birefringence ne - no using δ = 2π (ne - no)(d1 - d2)/λ, where d1 - d2 is a thickness difference of
two stacked MgF2 waveplate. One of the difficulties
in this measurement is the assignment of phasewithout 2π ambiguities. To achieve this, we measured
several waveplate samples with different thickness
differences (see [2] for more detail).

MgF2 with
AOI=59deg Photodiode(t=0.3mm) for monitor
Waveplate sample(t=1mm)

g

MgF
with
2
AOI=59deg(t=15mm)MgF 2 with
AOI=59deg(t=15mm)
Not to scale

PhotodiodeFig. 1. Schematic of the experimental setup.
0.0050ne - n o

0.00450.0040Sampled in 0.05 nm steps
Sampled in 0.02 nm steps
Derived from fitting fordata sampled in 0.02 nm steps
Laporte et al. (1983)
Chandrasekharan & Damany (1969)

0.0035
121.2

121.4

121.6

121.8

wavelength [nm]122.0

Fig. 2. Birefringence of MgF2. Values measured inprevious studies [3, 4] are also shown.
[1] R. Kano et al., SPIE 8443 (2012) 8443F.
[2] R. Ishikawa et al., Appl. Optics. 52 (2013) 8205.
[3] V. Chandrasekharan and H. Damany, Appl. Opt. 8(1969) 671.
[4] P. Laporte et al., J. Opt. Soc. Am. 73 (1983) 1062.

45

Ⅲ -1