MOGlabs MOA, Manual, Page: 23 / 66

4.2 Substantial adjustment to seed alignment
13
9. Remove input isolator 2 (if installed between
M1
and
M2
), preferably
by removing the entire isolator, ring clamp and right angle bracket
as one assembly. First ensure the isolator inputs and outputs are
covered to protect against items being magnetically attracted into
the isolator optics. Please take care if using steel tools and removing
screws, to avoid magnetic attraction into the isolator optics.
10. Pre-align the seed laser beam and the reverse propagating
TA
beam
using
M1
and
M2
. The beams should be collinear and overlapping at
locations
A
and
C
in fig. 4.1.
11. Re-install input isolator 2 if applicable, ensuring the seed laser is
well-centred on the input and output isolator apertures. The isolator
end faces should generally be orthogonal to the propagating beam
direction.
12. Measure the transmission efficiency of the Faraday isolator(s). If
the amplifier configuration has two input isolators, the isolator close
to the seed laser should be installed first. Compare the isolator
efficiency with the efficiency value specified in the system test report.
If the value from the test report and the measured efficiency are
different by more than 10%, contact
MOGL
abs customer support.
13. Remeasure the seed laser power before the
TA
diode (after the input
isolator) and adjust the seed laser current to achieve the same power
specified in the system test report. The seed laser should still be
stable, not near a mode-hop.
14. The
TA
injection current should now be chosen to match a value in
the table
Guide for seed coupling at low and high tapered amplifier
current
from column
TA current (mA)
in the test report.
15. Using
M1
and
M2
accurately align the seed laser beam with the
TA
reverse propagating beam using the following
walking
procedure:
(a) Make sure the seed laser is incident and centred on the
TA
block input aperture by adjusting
M1
and
M2
.