LOFT, Large Optics Fabrication and Testing group with OEFF & … · 2016. 9. 1. · zTrade study...
Transcript of LOFT, Large Optics Fabrication and Testing group with OEFF & … · 2016. 9. 1. · zTrade study...
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Fizeau or Twyman-Green?
Masaki Hosoda05/27/2010
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Outline
BackgroundPurpose of this presentationImportant points for an interferometer
Trade studyGhostSpatial frequency
Summary
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BackgroundIn the 3rd case study of OPTI524A, my team’s tasks were
Design an interferometerBuild an interferometerMeasure a roundness of Silicon Nitride ball.
I learned a lot I should care.Then,,,
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Purpose of this presentation
Summarize important points when we design an interferometer.
Trade study (Fizeau or Twyman-Green?)GhostSpatial frequency
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1. Trade study (Fizeau)
Source
BS
UUT
CCD
Reference
Advantage
Long Common Pass
drawback
High Stray Light Effect
(Long Coherence ~150mm)
Common Pass
75mm
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1. Trade study (Twyman-Green)Reference
Source
BS
UUT
CCD
Common Pass
Advantage
Low Stray Light Effect (Short Coherence ~50um)
drawback
Short Common Pass
OPL_reference
OPL_uut
Since Stray Light Effect in Fizeau was large,we chose Twyman-Green Interferomenterin OPTI524A.
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2. Ghost
Source
BS
UUT
CCD
m x D_source
CCD
Extended SourceBump
OPD can be washed out
Trade off
Reference
Extended source also wash out visibility of interferogram.
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3. Spatial frequency
sin mm dλ θ=[ ][ ] [ ]2
20100
mmd um
cycles≤ =
[ ][ ] [ ]1
1 0.5sin 0.025
20ummNA rad
d umλθ
⋅≥ = =
UUT
Assumptions
•UUT has sinusoidal surface irregularity.•Our target of spatial frequency is more than 50 cycles/mm.
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3. Spatial frequencyReference
Source
BS
UUT
F=100mm
F=75mm
This Field Stop (1.4mm) can define spatial frequency for a measurement.
F=300mm
F=50mm
CCD
f/5
NA=0.025
Aperture (100um)
MicroscopeObjective lens
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Conclusion
Summarized important points when we design an interferometer.
Trade studyFizeau has long common pass but need long coherence.Twymann-Green does not need long coherence but has short common pass.
GhostExtended source can reduce ghost effect but has trade off.
Spatial frequencyWe should consider spatial frequency for measurements
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Our System
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Uncertainty (temporal)
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Uncertainty (pattern)
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Surface Irregularity 1
Calibration Data Data (8 x 10 times)
15Calibration Data Data (8 x 10 times)
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Surface Irregularity 2
5.81 nm RMS
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Comparison Table
LongCoherence
ShortCoherence
SmallSource
FZ / TG(Ghost)
TG(Power)
BigSource
TG(Path Matching)(Stray Light)
TG(Path Matching)