AMULET
Advanced Metrology Using
LasEr Tracers
John Dale
Project Aim
• To take Frequency Scanning
Interferometry (FSI) from the lab into a
product
2
Frequency Scanning Interferometry
(FSI) Absolute measurements
Tunable Laser
• Used for several projects in
Oxford
Intensity
Reference
Interferometer: L
– ATLAS
– LiCAS
– MONALISA
Time
• Ratio of phase advance is
equal to the ratio of the lengths
Measurement
Interferometer: D
Intensity
• Reference interferometer is an
absolute length scale
– Can determine D if L known
• Scalable
– Any number of measurement
interferometers
Time
Measurement Interferometer: D2
3
Project Tasks
• Improve FSI Technique
• Practicality
• Stability
• Traceability
• Implement FSI in a laserTRACER
• Reduce equipment cost
• Simultaneous multiple length-measurements
4
LaserTRACER
• Developed by NPL, PTB and
marketed by Etalon AG
– A self tracking laser interferometer
– Automatically follows retro
reflector
– Uses differential interferometry
with a frequency stabilised laser
Intensity
Frequency Stabilised
Laser
5
Time
Why Absolute Measurement?
• Differential measurement
– laserTRACER tracks retro reflector
• If Absolute measurement system added
– No problems with beam breaks
– Switch from one target to the next
– Divergent beam allows simultaneous measurements
6
Current Reference Interferometers
• Evacuated folded path
reference interferometers
– Bulky
– Expensive
– Difficult to thermally stabilise
• We require
– Compact
– Can be thermally stabilised
– Long term stability
1.2m
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Compact fibre reference
interferometer
• Fibre Reference Interferometer
– Compact (Coiled)
– Cheaper
– Dispersion
• Experimental Prototype under
construction
– Fluid bath
– Insulated
– Temperature monitored
• Optical length with submicron
stability
• To be developed into a product
8
LaserTRACER Implementation
• Install into LaserTRACER head
• Take advantage of:
– Tracking capabilities
– Stabilised construction
– Market presence
• Many possible configurations
• Multiple measurement
interferometers
9
Reduced Laser Cost
• Working with laser manufacturers
– Produce simpler stripped down frequency
scanning lasers.
– Lasers which better suit FSI
• Laser is significant cost, reduction could
open other markets.
10
Why are they useful
• Particle Accelerator/Detector Alignment
• CMM and CNC Calibration
– Require calibration 1-4 times per year
– With absolute measurement capabilities, calibration much
quicker
• Combined CMM and CNC machines.
– Absolute distance measurements capability
– Especially interesting at large machines (20-30m)
– Small machines if cost reduced.
• Metrology assisted assembly
– Fitting of aeroplane wings
11
Summary
• Project will lead to a product: FSI enhanced
laserTRACER
• Generate Intellectual property
• NPL and Etalon AG have established market
presence
• laserTRACER has an established customer
base
• On the market in 4-5 years
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