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4.2 Substantial adjustment to seed alignment
11
ment, the
TA
diode has been replaced or under instruction by
MOGL
abs
support.
For most
MSA
systems, optical element
M1
is a partially reflecting fixed-
ratio beam-splitter. The transmitted part of the seed laser beam (location
B
in fig. 4.1) can be used for the following steps in seed alignment. If
M1
is instead a mirror, the seed laser beam can be accessed by inserting a
mirror directly after the seed laser (location
A
in fig. 4.1) or between the
first input isolator and
M1
. If substantial adjustments are needed, remove
M1
.
To obtain effective seeding of the
TA
diode:
1. Take note of the
Maximum current, unseeded
listed in the
MSA
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 step 1, preferably after the isolator at
location
E
in fig. 4.1.
NOTE: Measuring the
TA
output power before isolator could damage
the
TA
diode with a back-reflection from the power sensor. Take care
to avoid normal incidence reflections.
NOTE: If a sufficiently slim power sensor is not available, insert
a mirror in the beam path after (preferably) or before the output
isolator to deflect the beam to a larger sensor.
NOTE: Ensure that the
TA
output propagates through the isolator
without clipping.
3. Power on the
TA
diode with an injection current less than the
Max-
imum current, unseeded
. Adjust for a few mW in the reverse propa-
gating
TA
beam at location
C
in fig. 4.1.
4. Adjust the seed laser current/power so that it matches the minimum
listed value from the table
Guide for seed coupling at low and high
tapered amplifier current
in the system test report, typically 10 mW
(20 mW for some
TA
diodes). The seed laser should be stable in