SSRF Long Trace Profiler with an innovative design

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SSRF Long Trace Profiler with an innovative
design
Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Tiqiao XIAO and Shaojian XIA
Shanghai National Synchrotron Radiation
Center Shanghai Institute of Applied Physics, CAS
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
What for?
SSRF Beamline Construction

• 2-30keV hard X-ray widely used
• grazing angle 2.56mrad is required
• strip like mirror around 1 meter long
• precision for surface profile reach 1mrad

• widely use of bent mirror
• dynamic measuring of mirrors under different
  moment
• dynamic measure the effect of gravity compensation

• mirrors with large size and high precision
• difficult to control the quality for suppliers in
  the world

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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Table 1. Long mirrors for the first set of
beamline at SSRF
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
laser beam
scanning
surface under test
mirror
gravity
compensator
compensator
Figure 1. Setup for measurement to the
compensation of mirror gravity
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Requirements on metrology instrument

• Large scanning range 12 m
• high repeatability 1mrad
• high resolution 0.1?0.2mrad
• applicable for measurement on mirrors with
  different surface profile

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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001

• Available commercialized instruments,such as
  WYKO,ZYGO et al.,their characteristics
• wide beam,in principle size of elements measured
  equals to beam size
• applicable for regular profile measurement
  generally
• expensive for large caliberF152 (1 million RMB)
• 
  F600(1 million USD)

Blind alley!
Pave a different way
Scan with a pencil beam LTP
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Table 2. Some of LTP in the world
Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
During RD of SSRF, we wanted to do something.
We decided to develop a long trace profiler by
ourselves.
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Goal
Preliminary scanning range 1.2m
repeatability 1.0mrad resolution
0.1mrad
In fact scanning range 350mm
repeatability 3.0mrad resolution
0.5mrad
develop an LTP on the basis of successful solve
of some key techniques
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001

• Key techniques to be solved
• f-q system based on phase plate diffraction
• compensate to system errors employing area array
  CCD
• approaches to reduce the effect of environmental
  noises, such as temperature shift, air
  turbulence et al.
• software amend to system errors
• data collection and processing

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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Principle for measuring minute profile change
with pencil beam

detector
q
P
2q
d
P
q d/2l
Set d9mm,l 10m, detectable maximum change
0.45mrad correspondent minimum radius 2.3km
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001

• The supreme problem is how to measure d value
  precisely

• Factors that affect
• sourcefrequency,polarization,spatial mode
• light transmit mediaair turbulence,temperature
  shift
• mechanic stabilityvibration,inertial stress
  release
• optical elementsmaterial uniformity, process
  quality
• detectorssignal-to-noise ratio,dynamic range
• approaches for data processing

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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Schematic diagram proposed by Bieren
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
ppLTP by Qian Shinan et al.
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Disadvantages of ppLTP

• Sensitive to environmental noises, such as
  temperature shift, air turbulence
• strict requirements on the light source stability
  in frequency, spatial mode, polarization et al

We have to keep cautious to every step during
measuring
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001


BS
x
z
PP
y
f

FT Lens
Focal Plane
SUT
Diode Laser
Optical fiber
Schematic diagram for the innovative design of
SSRF LTP
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Advantages of our design

• Restricts on light source greatly decreased
• Effect of environmental factors on precision
  greatly reduced,insensitivity to noises improved
• Instrument structure simplified

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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Results
Repeatability
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Nominal parameters for SSRF LTP
Scanning range10350mm Accuracy 0.5mrad Static
stability0.1mrad/200s Acceptance
8mrad maximum measurable mirror
length1200mm Profilearbitrary
Measuring environment Room with no air
condition and with 1-2 person in
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Future plan
Develop a Long Trace Profiler with 1.5 meters
scanning range, employing the phase-plate
diffraction based f-q system
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Acknowledgement
Fruitful discussion with Dr. A.K.Freund, Dr.
O.Hignette from ESRF are highly appreciated
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Shanghai Symposium on Intermediate-energy Light
Source 2426/9/2001
Thanks!