MONALISAan Update

David Urner

Paul Coe

MatthewWarden

Armin Reichold

Monitoring, Alignment & Stabilisation with high Accuracy

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MONALISA

• Is an interferometric metrology system for continuous monitoring of position critical accelerator components

• Consists of a fixed network of evacuated interferometric distance meters

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Concepts

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QD0

Shint

ake

Mon

itor

Table

Compact Straightness MonitorVery Schematic View of ATF2 Setup

10cm

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Compact Straightness Monitor

• 6D position transferred from left to right– breaking of symmetries is important

• Preliminary simulation results of CSM Resolution: – y:10nm – distance meter resolution: 1nm = Resolution in z-direction– Positional change of optics components with respect to each other: 1nm. That’s the challenge!

10cm

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Measurement lines

We measure distances along measurement lines using two techniques:•Absolute distance interferometry <m resolutions•Displacement interferometry nm resolutions

Each line is the same, and is capable of performing both types of measurement.

Absolute distanceDisplacement

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Interferometer operation

Intensity

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Interferometer operation

Phase = 2π (Optical Path Distance) / Wavelength

Φ = 2π D / λ = 2π D (ν / c)

D = (c/ 2π) (ΔΦ/Δnu)

R = (c/ 2π) (Δθ/Δnu)D = R (ΔΦ/Δθ)

ΔD = (c/2π ν) ΔΦ

Fixed Frequency Interferometry

Frequency Scanning Interferometry

frequeny scanning

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Distance meter

• Measurement Frequencies:– FFI: up to 10kHz– FSI: up to 1Hz

• Long term stability determines low frequency behaviour– Minutes possible– Lot of work needed to extend to hours or days.

• Advantage of interferometric measurement system is fairly low cost per line.– Use of telecom frequency allows use of cheap commercial

hardware– Cheap amplification of light– Current estimate: as low as £800 per distance metre

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Current Status

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Vacuum System

8 way fibre ribbon

Tapered hole

Vacuum vessel wall

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First Measurements

in Vacuum

• Unexpected mechanical behaviour

• Tensioning of a drum – more mechanical

vibrations in vacuum– Hard to separate these

from resolution effects

• Need for vibration isolation and possibly damping

Cha

nge

in L

engt

hM

easu

red

Fre

quen

cy

Pressure1 Atm vac

Vacuum features

air

Atm Vac

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Atm vac

Changing Pressure

• Good agreement between FSI and FFI

• Decent correlation between pressure and measured OPD

Displacement (microns)

-0.2 0 0.2

Calculated overall change: 69m

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FSI• Dominated by actual vibrations!

– Need damping

– Need better launch head

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Compact Launch Head

• Launch Head needs following features:– Compact– Stable/rugged

• Temperature• Vibrations

– Cheap• Prototype:

– Adjustable– Currently being built

• Future: Jig to position– Glue components onto

substrate

Titanium

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Fixed Frequency Interferometry• Improvement of amplifier to reduce temperature

dependence• Test of Amplifier for White Noise behavior:

– Linear with laser power– With high laser power translates to 1pm/√Hz

• Spectrum above 1kHz seems to be white noise dominated

• Spectrum below 1kHz clearly vibration dominated– Vibration Isolation– Stable launch head

• Eventually see effects from– Air turbulences– Laser frequency instabilities

0 1 2 3 4 5 Frequency [kHz]

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Frequency Stabilisation• Lock laser to spectral feature of rubidium• Use a frequency doubling crystal to reach this

frequency

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Frequency Stabilisation• All parts are at Oxford• Mechanical assembly in progress

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Old design

Vacuum System at KEK

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Double bellow system: - Advantage:

- smaller frame - Disadvantage:

- active feedback- slightly less good compensation of forces

New Design

Vacuum System at ATF2

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Double bellow system:

OpticsVacuum

Compensation Chamber2 Atmosphere pressure

Active feedback: - measure pressure in inner and outer bellow chamber - stabilize sum of pressures

+

Valve to air

Valve to pressured air

<< >>

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Summary

• Very first measurements in vacuum

• Compact Launch Head

• Frequency Stabilization

• Vacuum System for ATF2

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