MOGlabs MOA, Manual, Page: 24 / 66

14
Chapter 4. MSA: internal seed alignment
(b) Install a power sensor after the
TA
output, preferably after the
output isolator.
(c) For the
horizontal
axis first, adjust
M2
to achieve maximum
output power from the
TA
. Call this value
P
REF
.
(d) Make a small adjustment to the
horizontal
axis of
M1
in a clock-
wise direction such that the output power drops by no more than
25%. Take note of how much adjustment was made e.g.
1
16
turn
clockwise.
(e) Next adjust only the horizontal axis of
M2
to maximise the out-
put power from the
TA
. The adjustment range should be less
than half a turn of the actuator at this step, and this range
should reduce upon iteration.
(f) If the new measured power is greater than
P
REF
, this higher
power is the new reference power
P
REF
. Iterate steps 15d
and 15e until
P
REF
is maximised. It will be necessary to drop
the output power by less than 25% as the alignment improves,
e.g. 10% or 5%.
(g) If the new measured power after step 15e is instead lower than
P
REF
, readjust the horizontal axis of
M1
anti-clockwise to return
to the original angle (as noted at step 15d), then reoptimise the
horizontal axis of
M2
to return to
P
REF
. Now iterate steps 15d
and 15e with an
anticlockwise
adjustment at step 15d.
(h) Once
P
REF
is maximised, iterate steps 15d through 15g for the
vertical
direction.
(i) Iterate the horizontal and vertical alignment procedures above
until
P
REF
is maximised.
16. Check that the seed laser power before the
TA
(position
C
in fig. 4.1)
has not changed during the adjustment procedure and corresponds
to the seed power from the system test report. If it has changed,
again adjust the seed laser current so that the power at position
C
matches a listed value in the
Guide for seed coupling at low and high
tapered amplifier current
table in the system test report. Iterate the
walking procedure from step 15 again (with very small adjustments).