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10
Chapter 4. MSA: internal seed alignment
4. Power on the
TA
diode with an injection current of 100 mA less than
the
Maximum current, unseeded
. Adjust the seed laser current/power
so that it matches a listed value from the table
Guide for seed cou-
pling at low and high tapered amplifier current
in the system test
report, typically 10 mW (20 mW for some
TA
diodes).
5. Slightly adjust mirror
M2
first horizontally, then vertically, to achieve
the maximum possible
TA
power,
P
REF
. The power should be close
to the value in the table
Guide for seed coupling at low and high
tapered amplifier current
, either
After isolator
or
Before isolator
column, depending on where the
TA
output power is measured.
4.1.1 Abbreviated walking procedure
(a) Measure the
TA
output power while making small (e.g.
1
16
turn)
adjustments to the
horizontal
axis of
M1
until the output power
is maximised.
(b) Adjust only the horizontal axis of
M2
to further optimise
P
REF
.
(c) Repeat above two steps until
P
REF
is optimised.
(d) Repeat the above steps for the vertical axis of
M1
and
M2
until
P
REF
is optimised.
6. Compare the recorded power of the
TA
with the appropriate value
from the test report. A variation of 5% is acceptable.
7. Record a
TA
power vs.
TA
current curve of the seeded
TA
diode as a
future reference for comparison if system performance changes.
If the
TA
output power is far below the factory measured output indicated
in the system test report, proceed to section 4.2.
4.2 Substantial adjustment to seed alignment
Please
do not
proceed with the alignment steps below unless instructed
to do so in the previous section, there has been substantial seed misalign-