Cavity Locking by Piezo-Driven Mirror

Botao Jia

Duke University

Advisor: Dr. Nanda Sirish

HAPPEX Collaboration Meeting

Dec 1, 2006

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

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

Transverse mode Video

Fabry-Perot Cavity Basis

Longitudinal mode

Reflection

Transmission

Cavity length (nm)

266nm

Eorror Signal

Piezo Scan Voltage

Reflection

Transmission

Measuring Longitudinal Mode by Scanning Piezo Voltage

Reflection

phase

Transmission

Characteristic signals of a Fabry-Perot Cavity

Cavity length (nm)

=532nm, Reflectivity=99.85%, Finesse 2000

Reflected Intensity

Detuning Parameter

phase

Measuring error signal in scan mode

Reflection

Error signal

Transmission

Quasi-stable locking has been achieved by using the “laselock” box in a feedback loop with the piezo driven mirror.

Experimental setupFeedback signal

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