MOGlabs MOA, Manual, Page: 32 / 66

22
Chapter 5. MOA: external seed alignment
installed, this distance will be quite short). To optimise the align-
ment, use a
walking
procedure as follows, where
M1
and
M2
refer to
external mirrors in the case of
MOA(C)
.
(a) Make sure that the seed laser beam is incident and centred at
the
TA
block input aperture by adjusting
M1
and
M2
.
(b) Ensure a power sensor is installed after the
TA
output, prefer-
ably after the output isolator.
(c) For the
horizontal
axis first, adjust
M1
to achieve maximum
output power from the
TA
. Next adjust only the horizontal axis
of
M2
to optimise the output power from the
TA
. Call this power
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 8d and 8e
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 8e is instead lower than
P
REF
, readjust the horizontal axis of
M1
anti-clockwise to return
to the original angle (as noted at step 8d), then reoptimise the
horizontal axis of
M2
to return to
P
REF
. Now iterate steps 8d
and 8e with an
anticlockwise
adjustment at step 8d.
(h) Once
P
REF
is maximised, iterate steps 8d through 8g for the
vertical
direction.
(i) Iterate the horizontal and vertical alignment procedures until
P
REF
is maximised.