MOGlabs MOA, Manual, Page: 22 / 66

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Chapter 4. MSA: internal seed alignment
power and frequency, i.e. not near a mode-hop and not ramping the
piezo.
5. The divergence of seed reverse propagating
TA
beams should be
matched. Remove
M2
and the input side chassis endplate, or use a
mirror to deflect the seed beam out of the chassis. Check the collima-
tion of the seed laser using a shear plate (shearing interferometer)
or
M
2
beam profiler and if necessary adjust the focus of the seed
laser to achieve collimation (refer to the
CEL
manual). If a shear
plate or
M
2
beam profiler is unavailable, the spot size of the seed
laser beam should be minimised at 5 m distance from the seed laser.
6. The reverse propagating
TA
beam is collimated with an input lens
mounted in a flexure translation mount. Allow the reverse propagat-
ing beam to propagate about 5 m, again by inserting a mirror into
the beam path to deflect the beam as required. Adjust the reverse
propagating beam divergence by rotation of the
TA
input lens mount
using the supplied lens tube spanners (see fig. 1.2 and fig 4.2). There
is an outer tube spanner for loosening the retaining lock ring and
an inner tube spanner for adjusting the lens focus. Make sure to
tighten the retaining ring once the lens position has been adjusted.
The beam spot size should be as small as possible at about 5 m
propagation distance.
7. Using the flexure alignment screws (see fig. 1.2), adjust the input lens
x − y
position so that the reverse propagating beam exits parallel to
the
MSA
chassis horizontal plane and parallel with the
MSA
chassis
long edge. It will be necessary to remove the input end plate from
the main chassis.
NOTE: The
TA
diode injection current should not be more than
Max-
imum current, unseeded
. Do not allow the
TA
reverse propagating
beam to propagate into the seed laser without a seed isolator in-
stalled; it could damage the seed laser diode.
8. Re-install
M2
, ensuring the incident beams are centred on the mirror
and are at 45
◦
angle of incidence.