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Cavity Locking by Piezo-Driven Mirror
Botao Jia
Duke University
Advisor: Dr. Nanda Sirish
HAPPEX Collaboration Meeting
Dec 1, 2006
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While the Prometheus Laser is away for fixing,
we studied cavity locking with:
• Medium finesse mirrors
• Piezo-driven mirror (designed by Gavalya)
• Non tunable, low cost laser
• Electro optic modulator
• Laselock electronics
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Transverse mode02 2
2
2
2
2
2
2
2
Ekc
n
y
E
x
E
z
Eik
z
E
Fabry-Perot Cavity Basis
YX
Z
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Transverse mode Video
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Fabry-Perot Cavity Basis
Longitudinal mode
Reflection
Transmission
Cavity length (nm)
266nm
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Eorror Signal
Piezo Scan Voltage
Reflection
Transmission
Measuring Longitudinal Mode by Scanning Piezo Voltage
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Reflection
phase
Transmission
Characteristic signals of a Fabry-Perot Cavity
Cavity length (nm)
=532nm, Reflectivity=99.85%, Finesse 2000
Reflected Intensity
Detuning Parameter
phase
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Measuring error signal in scan mode
Reflection
Error signal
Transmission
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Quasi-stable locking has been achieved by using the “laselock” box in a feedback loop with the piezo driven mirror.
Experimental setupFeedback signal
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Conclusion:
Locking is achieved. However, not very stable. Our home-made piezo doesn’t have good resolution for stable locking.
1. Laselock electronics performance in cavity locking need to be investigated further. So far we already gained lots of operating experience.
2. To try piezo with lower coefficient and higher resolution.
3. Now the Permethus laser is back. So to study and lock it to the cavity have the first priority.
Thank you