MOGlabs MOA, Manual, Page: 38 / 66

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Chapter 6. Output beam optimisation
movement of the cylindrical lens, adjustment of the
TA
output lens) or the
TA
diode has been replaced. It is non-trivial to achieve equivalent results
as represented in the system test report, so seek advice from
MOGL
abs
before proceeding.
6.1 Procedure for output beam optimisation
Please follow these steps to optimise the output beam.
1. Referring to the test report table
Guide for seed coupling at low and
high tapered amplifier current
, set the
TA
diode injection current to
a value where you expect a few mW
Unseeded
and no more than 10s
of mW
Before isolator
.
2. Cover the ends of the output isolator with e.g. masking tape and
carefully (it contains a very very strong magnet) store safely away
from metallic objects and optical benches.
3. Confirm that the
TA
output is incident exactly on the centre of the
cylindrical lens and the
TA
beam passes through the centre of the
output aperture on the amplifier chassis. If a photodiode in installed
in the
TA
output plate, the reflection from the cylindrical lens should
also be centred on this photodiode. If the
TA
beam is not centred on
the output aperture, adjust the vertical and horizontal alignment of
the
TA
beam with the fine-adjustment set screws on the top and side
of the U-chassis respectively (see fig. 1.2). If these adjustments were
not sufficient to recentre the beam, a more substantial adjustment
will be required as outlined below.
4. Reinstall and align the output Faraday isolator to maximise trans-
mission then set the
TA
current so that the
TA
is operating at no
more than 20% of full output power. Isolator alignment includes or-
thogonal translations, tilt (pitch and yaw), and rotation (roll) of the
entire isolator body. Transmission is typically 85 to 95% (refer to
the system test report).