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MONALISAan Update
David Urner
Paul Coe
MatthewWarden
Armin Reichold
Monitoring, Alignment & Stabilisation with high Accuracy
Nanobeam'08 D. Urner 2
MONALISA
• Is an interferometric metrology system for continuous monitoring of position critical accelerator components
• Consists of a fixed network of evacuated interferometric distance meters
Nanobeam'08 D. Urner 4
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
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
Nanobeam'08 D. Urner 9
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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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
Nanobeam'08 D. Urner 13
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
Nanobeam'08 D. Urner 16
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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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
<< >>
Nanobeam'08 D. Urner 22
Summary
• Very first measurements in vacuum
• Compact Launch Head
• Frequency Stabilization
• Vacuum System for ATF2