beamlines
Journal ofSynchrotron
Radiation

Design and performance of a new VIS–VUV
photoluminescence beamline at UVSOR-III

ISSN 1600-5775

Received 28 June 2013
Accepted 4 December 2013

Kazutoshi Fukui,a* Ryu-ichi Ikematsu,a Yoshinori Imoto,a Mamoru Kitaura,bKazumichi Nakagawa,c Takao Ejima,d Eiken Nakamura,e Masahiro Sakai,eMasami Hasumotoe and Shin-ichi KimuraeaFaculty of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan, bFaculty of Science,Yamagata University, 1-4-12 Kojirakawamachi, Yamagata 990-8560, Japan, cGraduate School of HumanDevelopment and Environment, Kobe University, 3-11 Tsurukabuto, Nada-ku, Kobe, Hyogo 657-8501, Japan,dInstitute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku,Sendai, Miyagi 980-8577, Japan, and eUVSOR Facility, Institute for Molecular Science, 38 Nishigo-Naka,
Myodaiji, Okazaki, Aichi 444-8585, Japan. *E-mail: fukui@fuee.u-fukui.ac.jp

A new bending-magnet beamline with a 2.5 m normal-incidence monochromator has been constructed to serve with a light source in the visible–vacuumultraviolet region for photoluminescence, transmission and reflection spectroscopies of solids at the UVSOR-III 750 MeV synchrotron radiation light source.
The aim is to pave the way to establishing a beamline with high photon flux, highbrilliance, high energy-resolution, high linear-polarization and low higher-order
light. To obtain high photon flux and brilliance, the acceptance angle of thebending-magnet radiation was designed to be 40 mrad (H)  14 mrad (V) andthe post-mirror system employed Kirkpatrick–Baez optics. The incidence angleof the incoming light to the optical elements, except to the gratings, was set toa grazing angle in order to keep a degree of linear polarization. For achieving
high energy-resolution, an off-plane Eagle-type monochromator was adopted.
Higher-order unwanted light in the energy range below  11 eV was suppressed
to be less than 0.1%.
Keywords: beamline; normal-incidence monochromator; photoluminescence.

1. Introduction

2. Design

Solid-state optical devices in the ultraviolet (UV) region havebrought about significant improvements in telecommunication, illumination, environmental and medical applications, and are expected
to lead to further progress. For technological and scientific researchon such industrially important UV materials, optical spectroscopic
instruments that cover a wide photon energy region, from the visible(VIS) to the vacuum-ultraviolet (VUV) regions, are required.
We have developed a new bending-magnet beamline, HOTRLU(High-resOlution Transmission, Reflection and LUminescence spectroscopies of solids in the VIS–VUV region), equipped with a 2.5 m
normal-incidence monochromator (NIM) at beamline BL3B ofUVSOR-III in order to realise accurate photoluminescence (PL)spectroscopy of such materials in the VIS–VUV regions. HOTRLU
has also been constructed as a succession beamline of BL1B (1 mSeya–Namioka-type monochromator beamline), which was closed
down at the end of March 2011. HOTRLU is featured as the third
specific VIS–VUV beamline at UVSOR-III: a multipurpose beamline(3 m McPherson-type monochromator beamline, BL7B; see Fukui etal., 2001), a variably polarized angle-resolved photoemission beamline with a 10 m modified Wadsworth-type monochromator(SAMRAI, BL7A; see Kimura et al., 2010), and a new PL-dedicatedbeamline (HOTRLU). In this report we describe the design details
and present performance of the HOTRLU beamline.

The beamline monochromator for PL measurements is required tosatisfy a wide photon energy range, giving a high brilliance on thesample, while maintaining a high degree of linear polarization, a highenergy-resolution and high purity (inclusion of less higher-orderlight). Thus we adopted the following target specifications for thebeamline using examples from the performance of the BL7B beamline: a photon energy coverage range of 2–24 eV, photon flux (E/E= 1000) higher than 1010 photons s1, energy resolution (E/E)
higher than 10000, beam spot size (H  V) less than 0.8 mm 0.8 mm, and degree of linear polarization higher than 0.7.
Since a NIM can maintain both incident beam profile and polarization of the outgoing beam, and the reflectivity is functional up to 30 eV, it is a good solution for achieving the above beamline
specifications. Considering the high-resolution specification, we adopt
an off-plane Eagle-type NIM (see Namioka, 1959). We use a verticaldispersion grating configuration where both entrance and exit slits
are located in the same plane. Even though the reflectivity of thenormal incidence is functional up to  30 eV, the square of thereflectivity on the higher energy side becomes low and is not
appropriate for PL measurements. Therefore, the layout of thisbeamline needs to consist of a normal-incidence grating with theother optical elements at grazing incidence. This configuration alsopreserves the degree of linear polarization of the bending-magnet

J. Synchrotron Rad. (2014). 21

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Table 1
Characteristics of optical components of the HOTRLU beamline.
Pre-mirrors

Incidenceangle ( )Radius (mm)Dimensions(mm)

Coating
material

M0
M1
M285
81.1
87

1 (plane)
773.60  32300 (toroidal)
1 (plane)110  300
210  28030  440

Au
Au
Au

Gratings

Deviation
angle ( )Radius(mm)Dimensions(mm)

Coating
material

Grooves(mm1)

G1
G2
G3

44
4

2500
2500
2500

40  11040  11040  110

Au
Pt
Al

1200
600
300

Post-mirrors

Incidenceangle ( )Radius (mm)Dimensions(mm)

Coatingmaterial

M3
M48286.5

9390 (spherical)
17090 (spherical)

40  400
50  270

AuAu

radiation. However, the floor shape at the beamline usually spreads
out toward the end of the beamline. This implies that the layout of theNIM beamline with normal-incidence grating configuration is disadvantageous because user experiment space becomes insufficient.
To avoid this, we rotate the monochromator and the post-mirror
system in the horizontal plane, and introduce a plane mirror into thepre-mirror system. This mirror also acts as a higher-order cut filter if it
is vertically split-coated. The optical layout in the vertical direction is
also designed to satisfy the following two conditions: (i) the output
beam of the HOTRLU beamline is horizontal, and (ii) the heightof the output beam is  1200 mm. These conditions facilitate PL
experiments on condensed matter. For the PL measurements, notonly a high photon flux but also high brilliance is required. Thus, forgood focusing at the experimental point we employ Kirkpatrick–Baez
optics (see Kirkpatrick & Baez, 1948). An optical layout simulation
was carried out using the ray-tracing program SHADOW (see Lai &Cerrina, 1986).
The adopted parameters of the optical components are listed
in Table 1, and the top and side views are schematically shown inFigs. 1(a) and 1(b), respectively. The acceptance angle of the beamline is 40 mrad (H)  14 mrad (V), which satisfies the prerequisite
photon flux. M0 is a plane mirror for changing the direction of thebending-magnet radiation at the point S and for reducing heat load.
A radiation shield wall is located in between the M0 and M1 mirrors,
where a toroidal mirror M1 focuses incoming bending-magnet
radiation to the entrance slit S1 (1 : 1) to prevent the focal spot shapefrom deforming owing to a wide acceptance angle. A plane mirror M2

reflects the light in the horizontal direction to reserve working spacearound the sample (Q) and to correct horizontal beam misalignment,
as mentioned above. An off-plane Eagle-type monochromator withfocal length of 2.5 m consists of S1, gratings G and exit slit S2. The
monochromator satisfies both F-number matching to the pre-mirrorsystem as well as the prerequisite resolution specification. We use
three gratings (G1, G2 and G3) with different grooves, blazing angles
and coatings to cover the wide photon energy region from 2 to 30 eV.
The horizontal deviation angle of G is 4 . The total rotation angle(angle resolution) of the gratings and total linear travel (travelresolution) of the grating chamber were 6 (0.036 ) and 20 mm(0.01 mm), respectively. Four optical low-energy-pass filters (LPFs),LiF, quartz, WG32 and OG52, are available and a motorized linear
actuator can set one of them just after S2, to reject higher-order lightin the low-energy region. The post-mirror system with Kirkpatrick–Baez optics consists of two spherical mirrors M3 and M4 whichcondense incoming light from S2 horizontally and vertically. The M4
mirror also realigns the beam parallel to the floor. Finally, the horizontally propagating beam is focused onto the Q point. Both theVIS–UV and VUV spectrometers with CCD sensors for PL
measurements can be placed in the sample chamber. The calculateddegree of linear polarization on the paraxial ray of this layout is
expected to be higher than 0.7 over the whole energy region.

3. Present performancesFig. 2 shows the throughput spectra measured at the Q point by a Si
photodiode (SPD; AX-UV100, IRD). The slit widths of S1 and S2
were set to 100 mm. The photon number estimated using the typicalquantum efficiency of AX-UV100 was  1  1010 photons s1 or
more over the whole photon energy rage from 1.7 eV to  35 eV, at abeam current of 300 mA, which is the typical current of the top-up
operation of UVSOR-III. Fig. 3 shows the system throughput with
the G3 grating for the above-mentioned LPF variation. The LPF cutoff photon energies are 11.8 eV (LiF), 7.7 eV (quartz), 3.9 eV(WG32) and 2.4 eV (OG52). We have confirmed that the intensity ofthe higher-order light is less than 0.1% of that of the first-order light;
thus we can obtain high-purity monochromated light by using theLPFs in the G3 range below  11 eV. This photon energy range isvery important for the PL measurement of solids.
Fig. 4 shows a contour map representing the beam spot profile atthe Q point, obtained by raster scan of a metallic plate with a 0.2 mmdiameter pinhole placed just before the SPD and measuring output
current. The profile shown in Fig. 4 was recorded using G2 at  12 eV( 100 nm). The full width at half-maximum (FWHM) of the profile

Figure 1
Schematic layout of the HOTRLU. (a) Top view and (b) side view. Dimensions aregiven in millimeters.

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Figure 2
Throughput spectra of the HOTRLU beamline.

Kazutoshi Fukui et al.  New VIS–VUV photoluminescence beamline at UVSOR-III

J. Synchrotron Rad. (2014). 21

beamlines

Figure 3

Figure 5

Throughput spectra with the G3 grating described in Table 1, measured with a lowenergy-pass filter.

Absorption spectrum in the spectral range of the Schumann–Runge oxygen
molecule band.

Figure 6
Photoluminescence (thick blue line) and photoluminescence excitation (thin blackline) spectra of a Gd3Ga3Al2O12 (GAGG) single crystal measured at 6 K. The
excitation energy of the PL spectrum and the emission energy of the PLE spectrum
are 6.52 eV and 3.92 eV, respectively.

Figure 4
Beam profile contour map image at the sample position measured at 100 nm using
the G2 grating described in Table 1.

was evaluated to be 0.75 mm (H)  0.25 mm (V). Beam profiles forthe other gratings were similar to that of G2 shown in Fig. 4.
However, for all gratings, profile deformations were clearly observedat the low photon energy limit.
The absorption spectrum of oxygen molecules in the spectral rangeof the Schumann–Runge bands, measured with G1 at slit widths S1and S2 of 50 mm, is shown in Fig. 5. Here the horizontal axis, representing wavelength, is not calibrated. In this spectrum the energy(wavelength) resolution (E/E) for 50 mm slit opening is roughly
5000 or more.
In Fig. 6 we show typical PL and PL excitation (PLE) spectra of a
Gd3Ga3Al2O12 crystal (GAGG; see Kamada et al., 2012) taken at theHOTRLU beamline. The sample size and the measurement
temperature were 10 mm  5 mm and 6 K, respectively. The PLspectrum (thick blue line) was measured using a 30 cm Czerny–Turner monochromator with an entrance slit width of 100 mm andwith a liquid-nitrogen-cooled back-illuminated CCD. The excitationenergy was set to 6.52 eV by G3, and both S1 and S2 were set to300 mm. A sharp PL peak at 3.92 eV was assigned to the 4f intraatomic emission of Gd3+ ions. The thin black line is a PLE spectrumof the sharp emission peak at 3.92 eV, which was measured up to30 eV by successively replacing the grating among the G3, G2 and G1J. Synchrotron Rad. (2014). 21gratings. In the PLE spectrum, sharp peaks owing to 4f intra-atomic
absorptions of Gd3+ ions and a clear sharp edge corresponding to theband-to-band absorption of the GAGG are clearly observed at
4–5 eV and at 5.96 eV, respectively. A gradual increase of the intensity in the higher energy range (> 20 eV) is also observed, which isinterpreted as the appearance of multiple electron–hole pairs inGAGG.

4. Summary
A new bending-magnet beamline at BL3B has been constructed(HOTRLU) equipped with a 2.5 m normal-incidence monochromator. The present performance of HOTRLU is as follows (theparameters in square brackets are our target performance at thedesign stage): photon energy coverage, 1.7–31 eV [2–24 eV]; photonflux (E/E = 1000),  1010 photons s1 (300 mA)1 over a wholeregion [ 1010 photons s1 (300 mA)1]; energy resolution (E/E)(G1, S1 50 mm, S2 50 mm),  5000 [ 10000]; beam spot size at asample position (H  V), 0.75 mm  0.25 mm [ 0.8 mm 0.8 mm]. Both the polarization evaluation and the resolution
improvement are future issues.
We gratefully thank Dr K. Kamada from Materials Laboratory ofFurukawa Co. Ltd for providing precious samples.

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Lai, B. & Cerrina, F. (1986). Nucl. Instrum. Methods Phys. Res. A, 246, 337–341.
Namioka, T. (1959). J. Opt. Soc. Am. 49, 460.

Kazutoshi Fukui et al.  New VIS–VUV photoluminescence beamline at UVSOR-III

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