AMULETAdvanced Metrology Using

LasEr Tracers

John Dale

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Project Aim

• To take Frequency Scanning Interferometry (FSI) from the lab into a product

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Frequency Scanning Interferometry (FSI) Absolute measurements

• Used for several projects in Oxford– ATLAS– LiCAS– MONALISA

• Ratio of phase advance is equal to the ratio of the lengths

• Reference interferometer is an absolute length scale– Can determine D if L known

• Scalable– Any number of measurement

interferometers

Tunable Laser

Reference Interferometer: L

Measurement Interferometer: D

Measurement Interferometer: D2

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Intensity

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Project Tasks• Improve FSI Technique

• Practicality• Stability• Traceability

• Implement FSI in a laserTRACER

• Reduce equipment cost

• Simultaneous multiple length-measurements

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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

Frequency StabilisedLaser

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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

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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

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LaserTRACER Implementation• Install into LaserTRACER head

• Take advantage of:– Tracking capabilities– Stabilised construction– Market presence

• Many possible configurations

• Multiple measurement interferometers

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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.

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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

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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