MOGlabs MOA, Manual, Page: 29 / 66

5. MOA: external seed alignment
WARNING
Do not operate the amplifier above the
Maximum current, unseeded
without an appropriately coupled input seed. Operation exceeding that
condition can cause fatal structural degradation of the
TA
diode. Refer to
the
Maximum current, unseeded
specified in the amplifier test report.
MOA
installation requires aligning a seed laser with the
TA
diode to obtain
a power comparable to the value in the
MOA
test report. The
MOA
is
available in three configurations:
MOA
,
MOA(L)
and
MOA(C)
. The
MOA(C)
does not have provision for an internally mounted output isolator, so the
user should provide an external isolator for both input and output beams.
5.1 Seed alignment
To efficiently couple seed light into the
TA
diode, polarisation and spa-
tial mode matching are required; that is, the seed beam and
TA
reverse
propagating beam should have the same polarisation, beam width, and di-
vergence. The
TA
input lens in the U-chassis (see chapter 1) is optimised
by
MOGL
abs for a collimated seed laser. Depending on the amplifier
configuration, the input seed laser could be fibre coupled or free space.
With reference to figure 5.1, optimise the seed alignment using the proce-
dure below.
1. Take note of the
Maximum current, unseeded
listed in the
MOA
test
report and the maximum expected output power at this
TA
current.
2. Terminate the
TA
output beam path with a power sensor rated to at
least the power noted in the above step, preferably after the isolator
at location
D
in fig. 5.1.
NOTE: Measuring the
TA
output power before isolator could damage
the
TA
diode with a back-reflection from the power sensor. Take care
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