MOGlabs FSC, Руководство пользователя

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4.2 Achieving an initial lock 27
Figure 4.2:
Scanning the laser with P-only feedback on the fast output
while scanning the slow output causes the error signal (orange) to become
extended when the sign and gain are correct (right). In a PDH application,
the cavity transmission (blue) will also become extended.
11. Some applications may benefit by increasing
FAST DIFF
to im-
prove loop response, but this is typically not needed to achieve
an initial lock.
4.2.2 Locking with slow feedback
Once lock is achieved with the fast proportional and integrator feed-
back, the slow feedback should then be engaged to account for slow
drifts and sensitivity to low frequency acoustic perturbations.
1. Set
SLOW GAIN
to mid-range and
SLOW INT
to 100 Hz.
2. Set
FAST
mode to
SCAN+P
to unlock the laser, and adjust
SPAN
and
OFFSET
so that you can see the zero crossing.
3. Set
MONITOR 2
to
SLOW ERR
and observe on an oscilloscope.
Adjust the trimpot beside
ERR OFFSET
to bring the slow error
signal to zero. Adjusting this trimpot will only affect the DC
level of the slow error signal, not the fast error signal.
4. Relock the laser by setting
FAST
mode to
LOCK
and make any
necessary small adjustments to
FREQ OFFSET
to lock the laser.