04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Electronic speckle pattern
interferometry at the SLHC
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Overview
• What is the SLHC?– How is Oxford involved?
• Electronic Speckle Pattern Interferometry (ESPI)– What is it?– How does it work?– How are we using it?
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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SuperLHC• ATLAS upgrade required
– Radiation damage ~10 years– Higher luminosity of SLHC
• ATLAS built for <700 fb-1
• SLHC must cope with >3000fb-1
→ New central tracker
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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The ‘stave’
• Detectors mounted on carbon fiber staves
– Low mass– Integrated cooling and services– Intrinsic mechanical stability
Bus cable
Hybrids Coolant tube structure
Carbon honeycomb or foam
Carbon fiberfacing
Readout IC’s
Silicon sensors
Staves inter-leaved
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Where does ESPI come in?
• Accurate track resolution– Need thermo-mechanical stability to -25°C
• ESPI can verify this– Sub-micron precision– Large area– Frequent sampling– Non-invasive
• Oxford has experience
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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How ESPI Works (1)
• An expanded laser beam on rough surface gives laser speckle
• Interference caused by λ scale variations on surface
How ESPI Works (2)
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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04/18/23 Robert King, Oxford University - Graduate Seminar Series
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How ESPI Works (3)
Initial pixel value
Final pixel value
|Subtraction|
Bright Bright Dark
Dark Dark Dark
Dark Bright Bright
Bright Dark Bright
→ Intensity contours = displacement contours
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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How ESPI works (4)
• Silicone diaphragm under pressure
• Each ‘fringe’ ~ λ/2 displacement
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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The Oxford Setup
• Sensitive to in-plane and out of plane motion
•In-plane •Out-of-plane
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Laser Fiber coupling
Camera Fibers
Test Object
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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In-plane deformation example
Video made by Sam Whitehead
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Summary
• Integrated stave forms part of the SLHC upgrade• Validate thermo-mechanical stability• ESPI gives submicron accuracy over large areas• Testing on prototype staves should begin soon
Images sourced from Daniel Buria-Clark’s Thesis
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Backup slides
• Out of plane measurement detail
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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In plane measurement detail
04/18/23 Robert King, Oxford University - Graduate Seminar Series
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Speckle pattern formation
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