In trying to engage the power stabilisation servo, we found that its behaviour was
somewhat erratic.  The servo would lock for brief periods of time before a low frequency
change would cause the servo to go out of lock.  Engaging the integrator, when possible,
did not prevent the low frequency fluctuation from knocking the servo out of lock.
Coincidentally the free running power fluctuations through the pre-modecleaner exhibited
large (~2-5%) fluctuations too.

    Thinking that these fluctuations were perhaps caused by diffraction effects associated
with the corona aperture within the laser, a number coronia apertures were tried and their
effects on the beam were examined with a CCD camera.  Whilst looking at the beam profile of
both the oscillator and the front end, it was observed that the profile of the front end
laser was terrible.  Whilst the beam profile from the oscillator was good, it would change
at random intervals.  The front end (seed) beam was re-aligned and the overlap between the
seed beam and the oscillator output improved.

    Without re-doing the mode matching to the pre-modecleaner, the pre-modecleaner was locked.
Its transmitted power appeared more stable.  The power noise spectrum after the pre-modecleaner
appeared more stable too.  The power stabilisation servo was engaged and could be locked.
Its behaviour was noticeably better than previously.

    We could not engage the frequency stabilisation, for reasons unknown at the moment.  But
we will pursue this later this morning.





Jason, Peter