Download SR Beamlines in the VUV

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Ｎ
KEK layout
PF-AR
PF-2.5GeV
Layout of the Photon Factory
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Synchrotron radiation beamlines
in the vacuum ultraviolet and
soft X-ray region
Kenji ITO e-mail: [email protected]
Photon Factory, IMSS, KEK, Tsukuba, Ibaraki 305-0801, Japan
Introduction
Optical elements
mirrors geometrical shape
reflectivity
grating basic understanding
geometrical optics  ray tracing
varied-line spacing grating
Monochromators
normal incidence type
grazing incidence type
Summary
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What is the role of beamlines for SR usage?
1) conducting SR from the storage ring to the
experimental stations
2) shaping SR beam, spatially and energetically,
to meet the experimental requirements
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Definition of VUV and SX
VUV: vacuum ultraviolet
EUV: extreme ultraviolet
SX: soft X-ray
VUV-SX photons cannot propagate in the atmosphere!!!
1 mm
SiO2
100 nm
10 nm
VUV
IR
UV
Extreme Ultraviolet
10 eV
Be
Soft X-rays
SiL
1 eV
1 nm
100 eV
0.1 nm
2a0
Hard X-rays
CK NK OK
1 keV
SiK
CuK
10 keV
D. Attwood, “Soft X-rays and extreme ultraviolet radiation” (1999)
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VUV-SX beamlines must be kept at
ultra-high vacuum (UHV)
1) To facilitate the propagation of the VUV-SX photons
2) Not to disturb the storage ring
no mechanically-rigid window is available!!!
3) To protect the optical elements from contamination,
oil-free primary pumps are recommended!!!
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Layout of a typical beamline
shielding wall
branch-beam shutters
main beam-shutters
X-ray Beamline
Hutch
SR
VUV Beamline
Interlock System
pre-focusing mirror
monochromator
post-focusing mirror
Construction of a VUV-SX beamline
What kinds of measurements are required?
Photon energy range
Photon flux
Beam size
Photon band width
Polarization
Purity
Coherence
Beamline optics
pre-focusing mirrors
monochromator
post-focusing mirrors
Light source
bending magnet
undulator
multipole wiggler
This procedure does not work for a multipurpose beamline.
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Optical elements
used in the VUV-SX beamlines
1) reflection mirrors as a focussing tool
2) diffraction gratings, zone plates, multilayered mirrors, filters and crystals as
dispersion tools
monochromators as a beamline system
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Mirrors for SR use
1) focusing of VUV-SX light by various shapes of mirror:
sphere, cylinder, parabola, paraboloid, ellipse, ellipsoid, toroid, etc
2) for better reflectivity in the VUV-SX region:
substrate: SiC, Si, SiO2, metal, other glass
coating materials: Au, Pt, Os,…
with modern technology:
1-m long mirrors available
surface roughness < 0.5 nm in rms
slope error < 1 mrad  beamspot size
Focusing mirrors of spherical shape
Astigmatism of spherical mirror
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Aberration of spherical mirror
A
Rowland
O


circle
B
C
AO  r
OB  rt
1 1
2
 
r rt R cos
1 1 2 cos
 
r rs
R
OC  rs
focussing plane
To avoid astigmatism:
Focusing mirrors of toroidal shape

source
r
focus
r´
1 1
2
 
r r ' R cos 
sagittal
R
tangential
1 1 2 cos 
 
r r'

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Parabolic mirrors to avoid aberration
In 2D focusing: paraboloidal
Y2=4aX
a=f cos2
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Elliptical mirrors to reduce aberration
F1
F2
(X/a)2+(Y/b) 2 =1
For 2D focusing: ellipsoidal shape mirrors
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Reflectivity of mirrors
Rs 
Rp
a 2  b 2  2 s cos   cos 2 
Rs=Rp2 for 45°
a  b  2 s cos   cos 
 a 2  b 2  2a sin  tan   sin 2  tan 2  

 Rs  2
 a  b 2  2a sin tan   sin 2  tan 2  


2
2

2a 2   n 2  k 2  sin 2 


2b 2   n 2  k 2  sin 2 

2

2

2
 4n 2 k 2 

 4n 2 k 2 

1
2
1
2




 n 2  k 2  sin 2 
 n 2  k 2  sin 2 
Complex refractive index
Ñ = n - ik
complex dielectric constant
complex atomic scattering factor
Reflectivity of gold at 21.2 eV
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1.0
0.8
Reflectivity
Rp
0.6
Brewster angle
Rs
Rp=0 for dielectric material
0.4
0.2
0.0
0
10
20
30
40
50
60
Incidence angle
70
80
90
Atomic scattering factor for Au
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~
F  f 1  if 2

f1  Z  C 
 2 m a ( )d
2
2
E


0
f 2  ( / 2)CEm a ( )
K  1    i
  Df1
  Df 2
~
N  n  ik
~2 ~
N K
Henke, Gullikson and Davis, Atomic Data and Neclear Data Tables, 54, 181 (1993)
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Reflectivity of gold
for s-polarization
N
M5
L3
Mirrors can play the role
of low pass filters.
1°=17.45 mrad
Henke et al., Atomic and Nuclea Data Tables, 54, 181 (1993)
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Surface roughness reduces the reflectivity
R=R0 exp[-(4s sinf/l)2]
s : micro surface roughness in rms <0.5 nm
f : glancing angle
glancing angle =1 deg
1.0
glancing angle =1 deg
1.0
Reflectivity
0.8
Reflectivity
5 deg
30 deg
0.6
5 deg
0.8
0.6
0.4
0.4
0.2
0.2
0.0
normal incidence
30 deg
normal incidence
0
2
4
wavelength (nm)
0.0
0
10
20
30
wavelength (nm)
40
6
50
8
10
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Gratings as
dispersion elements
Diffraction grating
Zone plate
Multi-layered mirror
Filters
Crystals
1) Introduction
2) Efficiency
3) Geometrical optics  ray tracing
4) Varied-line spacing grating
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Equation for diffraction grating
I a
2
sin 2 b / l sin   sin  sin 2  ND / 2
sin 2 D / 2
b / l 2 sin   sin 2
a: amplitude of incident light
D
2d
(sin   sin )
l
I has maximal values for D=2m.
40
d=5b
N=10
30
I
ml
sin   sin  
d
10
20
10
0
-4
-3
-2
-1
0
m
1
2
3
4
0
-1
0
1
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Dispersion of diffraction grating
sin   sin  
ml
d
 l 
d cos 
  
m
   
Angular dispersion:
Reciprocal linear dispersion:
 l 
10 6 d [mm ] cos  cos f
  
nm / mm
mr '[mm ]
 q  
Focal plane

q

r´
grating
f
Diffraction efficiency
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ml
sin   sin  
d
m=2 m=1 m=0
incident
light


m=-1
m=-2
m>0 positive order
inside order
m<0 negative order
outside order
Diffraction efficiency can be calculated by the scalar theory
for l/d<<1. Rigorous numerical calculations based on Maxwell
equations gives solutions with much better precision.
Note that the efficiency strongly depends on the polarization of
incident radiation.
Blazed grating
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Maximal efficiency can be achieved at
b
-b=b-.

mlbK=2dsinbcosK
where blazed wavelength is lbK
and deviation angle is 2K= -.

b
d
Calculated by M. Neviere
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Laminar grating(1)


Grating equation

i
sin+sin=ml/d
h
d
E0=100 cos2(d/2)
Em=(400/m22) sin2(d/2)
100
m=0
Efficiency(%)
80
d=(2/l)h(sini+sin)
Primary maximum
60
l/d=[2mcosi+(sin)/p]
40
m=1
20
0
0
Efficiency
×(p2/4+m2)
where P=h/d
2
4
6
3
10 l/d
8
10
12
Laminar grating(2)
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When the path difference
between 1 and 2 is equal to l/2,
destructive interference occurs.
1
2
i
h(sini+sin)= l/2

h
normal incidence: l=4h
grazing incidence: l=2h(i+)
Suppression of 2nd order!!!
Geometrical optics of
diffraction gratings(1)
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Fermat’s principle: the pathlength of an
actual ray traveling from a point A to a
point B takes an extremal or stationary
value.
dF=0, where F is the pathlength
from A to B. F: light path function
The red ray meets the grating at a point
P(,w,l) on the nth groove, the zeroth
groove being assumed to pass through O.
Two rays diffracted from the zeroth and
nth grooves are reinforced when their
path difference is equal to nml.
Light path function
F=AP+PB+nml
AP 
(  x ) 2  ( w  y ) 2  ( l  z ) 2
PB 
( x' ) 2  ( y' w ) 2  ( z' l ) 2
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Geometrical optics of
diffraction gratings(2)
Expansion of F for z=0 and n=1/d
1
1
1
1
F20 w 2  F02 l 2  F30 w 3  F12 wl 2
2
2
2
2
1
1
1
 F40 w 4  F22 w 2 l 2  F04 l 4  .....
8
4
8
F  F00  F10 w 
F00  r  r0 '
spherical aberration
ml
d
cos 2  cos  cos 2  0 cos  0




r
R
r0 '
R
astigmatism
F10   sin   sin  0 
grating equation
F20
defocus in y-direction
F02 
F30
cos  0
1 cos 
1



r
R
r0 '
R
sin 

r
 cos 2  cos 


r
R

 sin  0
 
r0 '

defocus in z-direction
 cos 2  0 cos  0


 r '
R
0





comma
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Geometrical optics of
diffraction gratings(3)
Apply Fermat’s principle to F
Fij
Fij
F
F
F
F
dF 
dw 
dl  0 
 0,
0
 0,
0
w
l
w
l
w
l
Rowland circle
Roland mount
r = R cos r0’ = R cos0
A
r
O


r0 ´
B
C
F20
cos 2  cos  cos 2  0 cos  0




r
R
r0 '
R
F30
sin 

r
 cos 2  cos 


r
R

 sin  0
 
r0 '

F20=F30=0
 cos 2  0 cos  0


 r '
R
0





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Geometrical optics of
diffraction gratings(4)
(L, M, N):direction cosine
Ray-tracing
F  AP  PB  nml
F

n
 ( L  L' )
 ( M  M ' )  ml
0
w
w
w
F

n
 ( L  L' )
 ( N  N ' )  ml
0
l
l
l
L'  L  T
n

T
w
w
n

N '  N  ml
T
l
l
M '  M  ml
(L´, M´,
N´)
1
T   p  p 2  eq 

e
2
2
     
e  1
  

w

  l 
n   
n   

p   L   M  ml
  N  ml 

w   w 
 l  l

2
2

n 
 n
 n  
2  n 
q  2m l  M
N
  ( m l ) 
   
l 
 w
 w   l  
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Geometrical optics of
diffraction gratings(5)
Equation of image plane:
x' cos( 0  f)  y' sin(  0  f)  r0 ' cos f
where
x'    L' d
y'  w  M ' d
z'  l  N ' d
r ' cos f   cos( 0  f)  w sin(  0  f)
d 0
L' cos( 0  f)  M ' sin(  0  f)
YZ-coordinate on S-plane
Y  ( y' r0 ' sin  0 ) sec( 0  f )
Z  z'

Y  r0 ' sec  0 secf  wf 100  w 2 f 200  l 2 f 020  lzf 011

 z 2 f 002  w 3 f 300  wl 2 f 120  wlzf111  wz 2 f 102  O w 4 / R 3

Y  r0 ' zg 001  lg 010  w lg 110  wzg101  w 2 lg 210  w 2 zg 201

 l 3 g 030  l 2 zg 021  lz 2 f 012  z 3 f 003  O w 4 / R 3


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Geometrical optics of
diffraction gratings(6)
S
F
SOURCE
By ray-tracing, it is possible to see
1) how the beam is focused on the slits
and at F,
2) how it spreads on the grating,
3) the geometrical through-put.
G
M
Spot diagram at exit slit
0.10
0.05
Y(mm)
M
S
0.00
-0.05
-0.10
-0.8
-0.4
0.0
Z(mm)
0.4
0.8
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Geometrical optics of
diffraction gratings(7)
Analytical expression for spot diagrams

Y  r0 ' sec  0 secf  wf 100  w 2 f 200  l 2 f 020  lzf 011
 z f 002  w f 300  wl f 120  wlzf111  wz f 102
2
3
2
2

 w4
 O 3
R

 

Z  r0 ' zg 001  lg 010  w lg 110  wzg101  w 2 lg 210  w 2 zg 201
 l g 030  l zg 021  lz f 012  z f 003
3
2
2
3
 w4
 O 3
R
Analytical merit function: Q
Q   Q l i 

 

i

 1


i  WLH
2
 (Y  Y ) dwdldz 
m
Z
WLH 
2

dwdldz

Optimization of design parameters so as to minimize Q,
where m is a weight function. Triple integrals have to be done
over the grating surface. Note that Y and Z are dependent
on li (i=1, 2, …N).
Masui and Namioka, JOSA, 16, 2253 (1999)
Geometrical optics of
diffraction gratings(8)
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Hybrid design method : Koike and Namioka, JESRP, 80, 303 (1996)
Yn ( w n , l n , z n )   f ijk w ni l nj z nk
n
Z n ( w n , l n , z n )   gijk w ni l nj z nk
n
Ray-tracing of 18 rays determines fijk’s and gijk’s by solving simultaneous equations.
Optimization process using the merit function in the same manner as before.
Ray-tracing program is available at http://www.xraylith.wisc.edu/shadow/shadow.html
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Varied line spacing gratings (1)
Groove function


1
nw , l s  w    n20 w 2  n02 l 2  n30 w 3  n12 wl 2
2
1

 n40 w 4  2n22 w 2 l 2  n04 l 4  ...
8



Effective grating constant
 nw , l  
s 1/

 w  w  l 0
sin+sin=l/s
=1 for mechanically ruled grating
=s/l0 for holographic grating
s
Varied line spacing gratings (2)
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HG´70
HG´90
n20  TC  TD ,
n30 
n40 
TC sin  TD sin d

,
rC
rD
4TC sin 2 
rC
2
Namioka and Koike, Appl. Opt., 34, 2180 (1995)
n02  SC  S D
n12 
SC sin  S D sin d

rC
rD
SC  S D
4TD sin 2 d TC
TD




2
rC
rD
R2
rD
2
2
.....
cos 2  cos 
TC 

,
rC
R
SC 
1 cos 

,
rC
R
cos 2 d cos d
TD 

rD
R
SD 
1 cos d

rD
R
Monochromators
in the VUV-SX region for SR use (1)
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Normal incidence monochromators
M. Koike, “Normal incidence monochromators and spectrometers” in J.A.R. Samson and D.L. Ederer Eds., “Vacuum
Ultraviolet Spectroscopy II in Experimental Methods in Physical Sciences” Vol. 32, (Academic Press, New York,
1998, Chapter 1, pp. 1-20 review
(A) Seya-Namioka type monochromator
(B) Pseudo Rowland mount monochromator
K. Ito, Y. Morioka, M. Ukai, N. Kouchi, Y. Hatano and T. Hayaishi, RSI, 66, 2119 (1995)
(C) Eagle type monochromator
1) 6.65-m Eagle at BL-12B of the Photon Factory
K. Ito, T. Namioka, Y. Morioka, T. Sasaki, H. Noda, K. Goto, T. Katayama and M. Koike, Appl. Opt., 25, 837-847 (1986)
K. Ito and T. Namioka, Rev. Sci. Instr., 60, 1573-1578 (1989)
K. Ito, K. Maeda, Y. Morioka and T. Namioka, Appl. Opt., 28, 1813-1817 (1989)
2) undulator based 6.65-m Eagle at BL9.02 of ALS
M. Koike, P. Heimann, A. Kung, T. Namioka, R. DiGennaro, B. Gee and N. Yu, NIM, A347, 282 (1994)
A.G. Suits, P. Heimann, X. Yang, M. Evans, C.W. Hsu, K. Lu, Y.T. Lee and A.H. Kung, RSI, 66, 4841 (1995)
D.A. Mossessian, P. Heimann, E. Gullikson, R.K. Kaza, J. Chin and J. Arke, NIM, A347, 244 (1994)
3) 6.65-m Eagle with varibale polarization undulator at SU5 of LURE
L. Nahon, B. Lagarde, F. Polack, C. Alcaraz, O. Dutuit, M. Vervloet and K. Ito, NIM, A404, 418-429 (1998)
K. Ito, B. Lagarde, F. Polack, C. Alcaraz and L. Nahon, J. Synchrotron Rad., 5, 839-841 (1998)
L. Nahon, C. Alcaraz, J-J. Marlats, B. Lagarde, F. Polack, R. Thissen, D. Lepere and K. Ito, RSI, 72, 1320 (2001)
Seya-Namioka monochromator (1)
2
I 200   F200 d
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2
1
I 200
I 200
I 200
 0,
 0,
0
r
r '
K
R/r=1.220527
R/r’=1.216931
2K=69.44°
Seya-Namioka monochromator (2)
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JASS2002
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1000 rays, generated from the entrance slit 10mm long, hitting the
1800-grooves/mm grating with 100(W)60(H) mm2 : from Koike’s review
conventional grating
holographic grating recorded
with a spherical wave front
holographic grating recorded
with an aspherical wave front
E/DE3600
VLS grating with straight
grooves
E/DE3104
Through put: 23%
Pseudo Rowland mount monochromator
Robin-Romand mount
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JASS2002
Oct 21, 2002
toroidal mirror
plane mirror
toroidal mirror
plane mirror
spherical grating
of R=3m
K. Ito, Y. Morioka, M. Ukai, N. Kouchi, Y. Hatano and T. Hayaishi, RSI, 66, 2119 (1995
Pseudo Rowland mount monochromator
F20
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cos 2  cos  cos 2  cos 




r
R
r'
R
Dth is calculated by F20=0.
2 and d are chosen so that
200nm
 D rr  D th 2 is minimized.
l  30nm
K. Ito, Y. Morioka, M. Ukai, N. Kouchi,
Y. Hatano and T. Hayaishi, RSI, 66, 2119 (1995)
With a 2400-l/mm grating,
E/DE3104 can be attained.
Off-plane Eagle (1)
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6.65-m off-plane Eagle spectrograph installed at the PF in 1983
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Oct 21, 2002
Off-plane Eagle (2)
0.1nm
0.1nm
Photographic
Photoelectric
Off-plane Eagle (3)
ALS
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Oct 21, 2002
Absorbed power density
of M1 and M2 are 10.4
and 7.6 W/cm2.
M1: spherical
M2: toroidal
M4: cylindrical
M5: cylindrical
M6: toroidal
Koike, Heimann, Kung, Namioka, DiGennaro, Gee and Yu, NIM, A347, 282 (1994)
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Off-plane Eagle (4)
VUV high-resolution beamlineAutoionization spectrum of neon (4300 l/mm grating)
with variable polarization at SU5
of SACO (LURE)
20x10
3
Slits 20
12d'
mm : FWHM (raw) = 0.22 meV
R ~ 97000
140
Slits : 10 mm
FWHM (raw) = 0.184 meV
R ~ 117000
120
ion yield (counts/sec)
13d'
18s'
100
80
60
40
10
20
14s'
0
21.6116
+
Ne Ion Yield (counts/sec)
15
21.6118
21.6120
photon energy (eV)
5
2
P 3/2
39s'
0
21.56
21.58
21.60
21.62
21.64
21.66
Photon energy (eV)
With a 4300-l/mm grating,
E/DE1.2105 can be attained.
Nahon, Alcaraz, Marlats, Lagarde, Polack, Thissen, Lepere and K. Ito, RSI, 72, 1320 (2001)
Monochromators
in the VUV-SX region for SR use (2)
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Grazing incidence monochromators
(A) Spherical grating monochromator (SGM) or Dragon
C.T. Chen, NIM, A256, 595 (1987); C.T. Chen and F. Sette, RSI, 60, 1616 (1989).
(B) SX700 (PGM, elliptical mirror) and modified SX700
H. Petersen, Opt. Com., 40, 402 (1982); H.A. Padmore, RSI, 60, 1608 (1989);
H. Petersen et al., RSI, 66, 1777 (1995).
(C) Monk-Gillieson type monochromator
M. Hettrick et al., Appl. Opt., 27, 200 (1988); M. Koike and T. Namioka, RSI, 66,
2114 (1995).
(D) Harada type monochromator (PGM)
T. Harada, M. Itou and T. Kita, Proc. SPIE, 503, 114 (1984); M. Itou, T. Harada and
T. Kita, Appl. Opt., 28, 146 (1989).
(E) Grasshopper monochromator: Rowland mount
F.C. Brown et al., NIM, 152, 73 (1978); F. Senf et al., RSI, 63, 1326 (1992).
SGM at the BL-16B of the PF (1)
Change the exit-slit position to
satisfy the condition of F20=0
Shigemasa et al., JSR, 5, 772 (1998)
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SGM at the BL-16B of the PF (2)
N2
Theoretical estimation for
resolving power
Ar
Shigemasa et al., JSR, 5, 772 (1998)
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SX-700
H. Petersen, Opt. Com., 40, 402 (1982)
F20
cos 2  cos  cos 2  cos 




r
R
r'
R
F20=0 with R=
r  r'
cos 2 
cos 2 
  r ' C 
C=2.25 high grating efficiency
rotation
tilting or rotation+translation
Modified SX-700
on-blaze type monochromator
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Padmore, RSI, 60, 1608 (1989); Petersen et al., RSI, 66, 1777 (1995).
M. Fijuisawa, private communication
Monk-Gillieson type monochromator
r
VLS plane grating
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Virtual image point
Source

Spherical mirror

r´
Spectral image point
cos 2  cos  cos 2  cos  mn 20l
Defocus term : F20 




r
R
r'
R
s
R=, =1 and m=+1
cos 2  cos 2  n20l
F20=0 at two wavelengths l1 and l2
F20 


r
r'
s
F30 and F40 can be taken into account, however, it is difficult to control.
Hettrick et al., Appl. Opt., 27, 200 (1988); Koike and Namioka, RSI, 66, 2114 (1995).
BL-11A (1)
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Kirkpatrick Baez optics
r=-r´ F20=0 at zeroth order and 500 eV
facilitate the optical adjustment
Amemiya, Kitajima, Ohota and Ito, JSR, 3, 282 (1996); Kitajima, Amemiya, Yonamoto
Ohta, Kikuchi, Kosuge, Toyoshima and Ito, JSR, 5, 729 (1998); Kitajima, Yonamoto,
Amemiya, Tsukabayashi, Ohta and Ito, JESRP, 101-103, 927 (1999).
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BL-11A (2)
transmission
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slit widths vs. resolution/flux
BL-11A (3)
N2 absorption
Other important points in the
construction of VUV-SX beamlines (1)
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Hardware design
Wavelength-scanning mechanism in monochromator: the
precision of grating rotation is in the order of 1/100 sec.
In-situ adjustment of optical elements, such as rotations
and translation.
Enclosing the important parts in a temperature controlled booth.
Isolation of optical elements
Optical elements or optical benches are well isolated from
mechanical vibrations caused by ventilators, mechanical
pumps, and so on. An ideal beamline is installed on a
massive concrete base.
Other important points in the
construction of VUV-SX beamlines (2)
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Installing beamlines
Anticipate how to align beamlines in its design stage.
Convenient tools for beamline alignment: theodolites and
auto-levels with a telescope and a laser
Optical alignment
VUV-SX photons are not visible!!!
Beam position monitors such as fluorescent screens,
photodiodes, and wire monitors are needed.
Other important points in the
construction of VUV-SX beamlines (3)
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Heat load on optical elements
Cooling system
For VUV-SX beamlines, direct cooling is difficult! In-Ga alloy
is used for better thermal contact between mirrors/gratings and their
water cooled holders. Entrance slits are often required to be cooled.
Thermal distortion
Selecting materials with small value for /k as substrate of mirrors
and gratings. SiC and Si are favored.
Simulation by ANSYS
Other important points in the
construction of VUV-SX beamlines (4)
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Specification of mirrors and gratings
Consult the makers about the micro roughness, slope error,
and groove density, of optical elements, for which the beamline
performance is strongly dependent.
Vacuum technology
Vacuum technology is well established to obtain 10-8 Pa (10-10 Torr).
Clean vacuum is obtained by oil-free primary pumps.
Contamination of optical elements.
cleaning with O2 discharge and UV-lamp.
Other important points in the
construction of VUV-SX beamlines (5)
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Control systems of beamline
PC-base control system for the monochromator
including the interface boards for stepping motors
and encoders
Beam channel?
Beamline interlock system to protect the
experimentalists from radiation hazards and to
avoid vacuum problems
Characterization of beamlines
Photon flux, resolving power, purity of light,
Reproducibility of the wavelength scanning
Fluctuation of the beam position on the entrance slit
Other important points in the
construction of VUV-SX beamlines (6)
Safety
Radiation safety
Gamma-ray stopper downstream of the first mirror,
which might be installed inside a cage
Flammable and toxic gases
Gas duct with a gas detection system
Exhaust steam from rotary pumps
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