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| In the old configuration of the 40m, the [[40m Lock Acquisition|locking acquisition]] of the Dual Recycled Michelson (DRM), is | In the old configuration of the 40m (2001-2009), the [[40m Lock Acquisition|locking acquisition]] of the interferometer works like this: the arm cavities are held out of resonance by adding an offset to of the Dual Recycled Michelson (DRM) is achieved |
3f Locking for the 2009 40m Upgrade
Introduction
With 3f locking people usually refer to a technique to lock an optical cavity of the interferometer. In that the optical cavity is locked by means of the error signal obtained by demodulating the signal from the reflection photodiode at 3 times the modulation frequency of the sideband.
This technique is different from the classical Pound-Drever-Hall locking technique. In that, by demodulating the signal from the reflection photodiode at the same frequency as that used to generate the sidebands, one obtains a signal proportional to the amplitude of the beat between the first order sidebands and the carrier. In the 3f locking, the main component extracted by the triple frequency demodulation is proportional to the beating between the first and the second order sidebands.
3f signals to lock the central part of the interferometer
In the old configuration of the 40m (2001-2009), the locking acquisition of the interferometer works like this: the arm cavities are held out of resonance by adding an offset to of the Dual Recycled Michelson (DRM) is achieved