MOGlabs MOA User manual

Amplified laser system
Model MOA/MSA
Revision 1.09

Limitation of Liability
MOG Laboratories Pty Ltd (MOGLabs) does not assume any liability aris-
ing out of the use of the information contained within this manual. This
document may contain or reference information and products protected by
copyrights or patents and does not convey any license under the patent
rights of MOGLabs, nor the rights of others. MOGLabs will not be liable
for any defect in hardware or software or loss or inadequacy of data of
any kind, or for any direct, indirect, incidental, or consequential damages
in connections with or arising out of the performance or use of any of its
products. The foregoing limitation of liability shall be equally applicable
to any service provided by MOGLabs.
Copyright
Copyright c MOG Laboratories Pty Ltd (MOGLabs) 2017 – 2019. No
part of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical, pho-
tocopying or otherwise, without the prior written permission of MOGLabs.
Contact
For further information, please contact:
MOG Laboratories P/L
49 University St
Carlton VIC 3053
AUSTRALIA
[phone]
[email protected]
MOGLabs USA LLC
419 14th St
Huntingdon PA 16652
USA
[phone]
www.moglabs.com

Preface
The MOGLabs MSA amplified laser system provides up to 4 W of tun-
able highly coherent optical radiation for atomic cooling, Bose-Einstein
condensation, ion trapping, and other spectroscopic applications. It re-
produces the optical spectrum of the input seed laser, maintaining the
linewidth while increasing the output power by up to 400 times (+26 dB).
It can be configured as amplifier only (MOA) or with cateye seed laser
(MSA). Options include fibre coupling, and input and output Faraday iso-
lators. The MOGLabs DLC and LDD drivers are ideally suited for operating
the seed and amplifier components of the MSA.
We hope that the MSA works well for your application, and please let
us know if you have any suggestions for improvement of the MSA or this
document, so that we can make life in the lab better for all.
MOGLabs, Melbourne, Australia
www.moglabs.com
i

ii

Safety Precautions
Your safety and the safety of your colleagues depends on careful attention
to proper operation of this product. Please read the following safety in-
formation before attempting to operate. Also please note several specific
and unusual cautionary notes before using the MOGLabs MSA and MOA,
in addition to the safety precautions that are standard for any electronic
equipment. The directions here apply to both MSA and MOA (amplifier-
only) configurations except where explicitly stated otherwise.
WARNING
Do not operate the amplifier without input seed laser. The input seed
power must be at least 10 mW, and properly mode-matched to the tapered
amplifier diode. Operation without appropriate seed can destroy the
tapered amplifier diode.
CAUTION
USE OF CONTROLS OR ADJUSTMENTS OR
PERFORMANCE OF PROCEDURES OTHER THAN THOSE
SPECIFIED HEREIN
MAY RESULT IN HAZARDOUS RADIATION EXPOSURE
Laser output from the MSA and MOA can be dangerous. Please ensure that
you implement the appropriate hazard minimisations for your environment,
such as laser safety goggles, beam blocks, and door interlocks. MOGLabs
takes no responsibility for safe configuration and use of the laser. Please:
•Avoid direct exposure to the output beams, both from the injection
seed input aperture and the amplified output aperture.
•Avoid looking directly into either beam.
iii

iv
•Note the safety labels (examples shown in figure below) and heed
their warnings.
•The MSA or MOA must be operated with a controller with keyswitch
interlock. The MSA must not be powered unless the keyswitch is
inserted and switched on. It should not be possible to remove the
keyswitch without turning off the power to the MSA or MOA.
•When the seed laser and amplifier are switched on, there should
be a delay of two seconds before the emission of laser radiation,
mandated by European laser safety regulations (IEC 60825-1).
WARNING Do not operate the amplifier without input seed laser. Then input
seed power must be at least 10 mW, and properly mode-matched to
the tapered amplifier diode. Operation without appropriate seed can
destroy the tapered amplifier diode.
NOTE The MOGLabs MSA and MOA are designed for use in scientific re-
search laboratories. They should not be used for consumer or medical
applications.
Protection Features
The MOGLabs MSA and MOA include a number of features to protect you
and the device. They should be used with a power supply that provides
additional safety features such as key lock operation, current limit, tem-
perature limit, cable continuity and short-circuit detection, soft-start and
turn-on delay.
Protection relay When the power is off, or the temperature controller is
off, the amplifier diode is shorted via a normally-closed relay.
LEDsSeparate LED indicators illuminate when the seed laser and amplifier
diode current supplies are enabled.

v
Label identification
The International Electrotechnical Commission laser safety standard IEC
60825-1:2007 mandates warning labels that provide information on the
wavelength and power of emitted laser radiation, and which show the
aperture where laser radiation is emitted. Figures 1 and 2 show examples
of these labels and their location on the MSA and MOA.
Model number: MSA003
Serial number: A41706001
Manufactured: JUNE 2017
Complieswith21 CFR 1040.10,and1040.11 except for
deviationspursuantto Laser NoticeNo.50, dated24June2007
MOG Laboratories Pty Ltd, 49 University St
Carlton VIC 3053, AUSTRALIA
AVOID EXPOSURE
VISIBLE AND INVISIBLE
LASER RADIATION IS
EMITTED FROM THIS APERTURE
Aperture label engraving
US FDA compliance
Warning and advisory label
Class 4
IEC 60825-1:2007
AS/NZS 2211.5:2006
VISIBLE LASER RADIATION
AVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT
Wavelength Max Power
665 − 675nm 600mW
Figure 1: Warning advisory and US FDA compliance labels.

vi
IEC 60825-1:2007
AS/NZS 2211.5:2006
VISIBLE LASER RADIATION
AVOIDEYE OR SKIN EXPOSURE TO
DIRECT OR SCATTEREDRADIATION
CLASS 4 LASER PRODUCT
Wavelength Max Power
665 − 675nm 600mW
IEC 60825-1:2007
AS/NZS 2211.5:2006
VISIBLE LASER RADIATION
AVOIDEYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT
Wavelength Max Power
665 − 675nm 600mW
Emission indicators
Model number: MSA003
Serial number: A41706002
Manufactured: JUNE 2017
Complieswith 21 CFR 1040.10, and 1040.11 exceptfor
deviationspursuant to Laser NoticeNo.50,dated24June 2007
MOG Laboratories Pty Ltd, 49 University St
Carlton VIC 3053, AUSTRALIA
Model number: MSA003
Serial number: A41706002
Manufactured: JUNE 2017
Complieswith 21CFR1040.10, and 1040.11 exceptfor
deviationspursuant to Laser NoticeNo.50, dated 24June2007
MOG Laboratories Pty Ltd, 49 University St
Carlton VIC 3053, AUSTRALIA
FDA compliance
and serial number
Laser warning advisory
Figure 2: Schematic showing location of warning labels compliant with Inter-
national Electrotechnical Commission standard IEC 60825-1:2007, and US FDA
compliance label. Emission indicator for seed laser (left) and amplifier (right).
Aperture label engraved on front and rear apertures; warning advisory label on
right hand side, compliance label left hand side near exit aperture.

Contents
Preface i
Safety Precautions iii
1 Introduction 1
2 First light 3
2.1 Basicsetup ............................ 3
2.2 Polarisation control . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Firstlight ............................. 5
3 MSA: internal seed alignment 7
3.1 Seed laser alignment . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Seedlaser............................. 7
3.3 Seedalignment.......................... 8
3.4 MeasurePIcurve......................... 12
4 MOA: external seed alignment 15
4.1 Seedalignment.......................... 15
4.2 MeasurePIcurve......................... 19
5 Output beam optimisation 21
5.1 Astigmatism............................ 22
6 Fibre coupling 23
6.1 Fibrealignment.......................... 24
6.2 Fibre coupler collimation . . . . . . . . . . . . . . . . . . . . 26
6.3 Polarisation control . . . . . . . . . . . . . . . . . . . . . . . 27
6.4 Troubleshooting.......................... 27
7 Diode replacement 29
vii

viii Contents
A Troubleshooting 31
B Electrical connections 33
B.1 MOA amplifier headboard . . . . . . . . . . . . . . . . . . . . 33
B.2 Connectorpinouts ........................ 35
C Chassis dimensions 37

1. Introduction
The MOGLabs MSA is a semiconductor laser amplifier with injection seed
laser. The MOA is an amplifier-only configuration of the MSA, without seed
laser. The amplifier block (see figure 1.1) consists of the core semicon-
ductor tapered amplifier diode and aspheric input and output collimation
lenses in flexure xy translation stages. A cylindrical lens at the output
provides astigmatism compensation and Faraday isolators protect the am-
plifier diode and prevent the amplifier output from disturbing the seed
laser. Fibre coupling options are available for the output and also for MOA
input with an external seed laser.
Output Faraday isolator
Input Faraday isolators(s)
Tapered amplier diode
Cylindrical lens
Seed laser
Output bre coupler
Amplier block
Input aperture and waveplate mount
Mirror M1
Mirror M2
Free-space
amplier output
Fibre
output
Figure 1.1: Schematic diagram of major components in the MSA, including ta-
pered amplifier diode, cylindrical lens astigmatism compensator, Faraday isolators
and seed laser.
1

2Chapter 1. Introduction
The tapered amplifier diode is user-replaceable (see chapter 7). Two flex-
ure stages control the transverse position of the input and output collima-
tion lenses, providing precise alignment with mechanical stability. Finely
threaded tubes control the focus of the lenses.
In normal operation, the seed laser produces a collimated beam with power
of 10 to 30 mW. The beam propagates through the first isolator, is deflected
by mirror M1 through a second isolator, deflected by mirror M2 into the
amplifier. If using an external seed laser, the seed beam will enter through
the input aperture in free-space or via a fibre coupler, then deflect from
M1. A 95:5 beamsplitter option can be used in place of mirror M1 to allow
free-space output of a fraction of the seed beam, for example to use for
locking to a frequency reference.
The seed laser beam must be mode-matched to the TA amplifier diode.
Mode matching can be checked by ensuring that the “tracer beam” output
from the ridge waveguide (input) of the TA back towards M2 and M1 is
overlapped with the seed beam propagating forwards. The seed and tracer
beams should have similar beam size along their paths, and should have
the same polarisation. See chapters 3 and 4 for more details.
The output from the TA diode propagates through a high-power Faraday
isolator and a cylindrical lens. The output from a TA diode is highly
astigmatic, expanding rapidly in one direction (the fast axis) and slowly
along the orthogonal (slow) axis. The aspheric lens on the output of the
amplifier is adjusted to collimate the fast axis, and thus over-focuses along
the slow axis. The cylindrical lens then collimates along the slow axis
only, producing a beam collimated in both transverse directions. The focal
length of the cylindrical lens is chosen to produce a beam as close as
possible to 1:1 aspect ratio; i.e. circular.
The output can then exit through the free-space output port, or be reflected
by mirrors M3, M4 to a fibre coupler. See chapter 6 for details on fibre
coupling.
For background information on tapered amplifiers, please see Refs. [1, 2].

2. First light
2.1 Basic setup
Initial installation of the device is typically a matter of mounting it to an
optical table and connecting to MOGLabs DLC and LDD controllers. Mount-
ing holes can be accessed by removing the cover, and M6 x 16 socket head
cap screws can then fix the device to the optical table. The hole spac-
ing also allows direct mounting to imperial tables for non-metric countries
(Burma, Liberia and the USA).
The MSA/MOA includes a water cooling channel for operation at unusually
high or low temperatures, or in laboratories with high or unstable air
temperature. Quick-fit connections are provided for connection to 6 mm OD
tubing, but for most applications, water cooling is not required; dissipation
to the air and/or optical table is sufficient.
1. The MSA or MOA should be firmly mounted to an optical table or
other stable surface, using the through-holes which have spacings
suitable for both metric and imperial tables.
2. The exit aperture should be directed towards a suitable power meter
or beam block.
3. Connect to MOGLabs DLC and LDD controllers, or to alternatives
using the connector pinout description in appendix B.
4. Enable the temperature controllers for seed and amplifier and check
that the temperatures are approaching their set points. Detailed
instructions for the controllers are provided in their associated user
manuals.
5. Check seed operation and alignment to the amplifier, as described
below and in the following chapters.
3

4Chapter 2. First light
2.2 Polarisation control
The polarisation of the seed and output beams can be controlled with half-
wave retarders. The seed polarisation must match the TA diode and con-
trol of the output polarisation can be useful for matching to polarisation-
maintaining (PM) singlemode fibre (see chapter 6).
For input polarisation control, a waveplate can be internal to the final
Faraday isolator (fig. 2.1) or to a waveplate holder mounted to the inside
of the chassis as shown in figure 1.1. On the output beam, a polarisation
rotator can again be an integral part of the final isolator for low-power
(<500 mW) devices. High power isolators do not have a suitable aperture
for mounting a waveplate, and instead the rotator should be be attached to
the chassis just before the fibre coupler. The test report provided with your
laser system will specify if waveplates have been added; please contact
MOGLabs if more information is required.
0.035” or
0.9mm hex key
λ/2 waveplate λ/2 waveplate
Figure 2.1: Two types of Faraday isolator. Each can be supplied with exit λ/2
waveplate inside one end-cap. The waveplate can be rotated to rotate the plane
of polarisation of the laser beam, for example to optimise coupling of seed into
the amplifier diode, or output beam into a polarisation maintaining fibre.

2.3 First light 5
2.3 First light
WARNING
Do not operate the amplifier above the maximum unseeded current speci-
fication without input seed. The input seed power must be at least 10 mW,
and properly mode-matched to the tapered amplifier diode. Operation
without appropriate seed will destroy the tapered amplifier diode.
For MOA with external seed laser, please proceed to the following chapter
(chap. 3). If you have an MSA, your seed and amplifier have been aligned in
the factory and only very minor adjustments should be required. However,
you should first check that the seed is operating correctly and that seed
and amplifier are at least approximately aligned.
1. Power on the seed laser and adjust for a few mW of output power.
Instructions on operation of the seed laser are provided separately
in the MOGLabs CEL cateye laser user manual. Please refer to the
supplied test report for nominal temperature and current settings,
and in particular be aware of the maximum current limit.
2. Measure the seed power before and after each isolator, and verify
that the beam is centred on the input to the amplifier block. It may be
necessary to use a video camera (e.g. webcam with IR filter removed),
or an infrared upconversion card, to see the seed beam.
3. Power on the amplifier diode and adjust the diode injection current
until a weak alignment (tracer) beam can be detected exiting from
the input side of the amplifier block. Do not exceed the maximum
unseeded current specified in the test data for your device (300 to
700 mA). Again, it may be necessary to use a video camera (e.g.
webcam with IR filter removed), or an infrared upconversion card, to
see the alignment beam.
4. Ensure that the tracer and seed beams overlap between isolator and
amplifier (the tracer beam should not propagate backwards through
the isolator). Both beams should have the same polarisation which

6Chapter 2. First light
can be checked using a sheet polariser (for example, a linear po-
larising filter from a photographic store). The beams should have
similar cross-sections.
If there is any concern that the system alignment has been disturbed
in shipping, please contact MOGLabs before proceeding to full seed
alignment described in chapters 3, 4.
5. If the alignment is good, arrange a power meter and recording device
(computer) to monitor and record the output power of the amplifier
for the following stages.
6. Increase the seed power to 15 mW measured at the input to the TA.
You should observe an increase of at least 50% in the amplifier output
power as the seed power increases from 1 mW to 15 mW.
7. Adjust mirrors M1, M2 to optimise the output power. Only very small
adjustments should be needed.
8. At the maximum unseeded injection current of the TA diode (see your
test report), ensure the TA is amplifying the seed by comparing the
output power seeded and useeded. Compare also to the output power
to the test results provided with your system. If the output power is
notably lower than expected, adjust the focus of the amplifier input
collimation lens and adjust mirrors M1, M2 to optimise the output
power. If unable to achieve power comparable to that of the factory
test report, please contact MOGLabs for advice.
9. If the output power is similar to factory results, then you can increase
the TA injection current while monitoring the output, until normal
operating conditions are achieved.
10. Please record a PI curve as a reference for comparison when system
performance changes. See section 4.2.

3. MSA: internal seed alignment
WARNING
Do not operate the amplifier above the maximum unseeded current speci-
fication without input seed. The input seed power must be at least 10 mW,
and properly mode-matched to the tapered amplifier diode. Operation
without appropriate seed will destroy the tapered amplifier diode.
3.1 Seed laser alignment
For the MSA, your seed and amplifier have been aligned in the factory
and only very minor adjustments should be required. Please do not pro-
ceed with the alignment steps below unless there has been substantial
misalignment, or the TA chip has been replaced. Refer to section 2.3 for
instructions on initial operation.
The following instructions apply if there has been major disruption to
the alignment, for example due to mishandling during shipping, or when
changing the TA diode.
3.2 Seed laser
Proper operation of the seed laser should be established prior to attempt-
ing operation of the amplifier. Instructions on operation of the seed laser
are provided separately in the MOGLabs CEL cateye laser user manual.
The seed laser beam can be accessed by insertion of a mirror directly after
the seed laser or first isolator, or if substantial adjustments are needed,
by removing the first mirror (M1) and opening the shutter on the MSA/MOA
input aperture. The seed laser should be stable, not near a mode-hop.
The beam profile should be similar to that of the output from the input
(ridge waveguide) side of the tapered amplifier (TA) diode, typically about
1×3 mm (1/e2full widths) and at least 10 mW power. The polarisation of
the seed laser beam must match that of the TA chip; a λ/2 waveplate will
7

8Chapter 3. MSA: internal seed alignment
have been inserted into the final isolator if needed (see your test report).
Please contact MOGLabs if further information is required.
3.3 Seed alignment
If the tapered amplifier (TA) diode is operated without injection seed, all
of the electrical input energy is lost as heat, and at high current there
is significant risk of damaging the diode. At currents over 300 to 700 mA
(device dependent), it is important that an injection seed laser beam is
coupled into the TA diode so that some of the input energy is converted to
optical output rather than heat. Follow these steps to align the seed into
the TA.
1. Insert a mirror after the seed laser to deflect the beam outside the
chassis, or remove mirror M1 to allow the seed laser beam to prop-
agate through the input aperture. Adjust the seed laser collimation
so that the beam is well collimated, or weakly focusing at a distance
of at least 4 m from the seed laser. Replace mirror M1.
OUTPUT ISOLATORLENSTA DIODE
INPUT
ISOLATORS
M1
M2
MSA INTERNAL
SEED LASER
M3
M4
Optional
Figure 3.1: Configuration of MSA with internal seed laser, two isolators, amplifier,
and output isolator.
2. Remove both input isolators between seed and amplifier. Ensure
the isolator inputs and outputs are covered to protect against items
being magnetically attracted into the isolator optics.
3. Adjust the TA diode injection current until a weak alignment beam can

3.3 Seed alignment 9
be detected exiting from the input side of the TA diode. Do not exceed
the maximum unseeded current specified in the test data for your
device (300 to 700 mA). It may be necessary to use a video camera
(e.g. webcam with IR filter removed), or an infrared upconversion card,
to see the alignment beam.
4. Arrange a power meter and recording device (computer) to monitor
and record the output power of the amplifier for the following stages.
5. The TA alignment beam will have an elliptical beam profile. If nec-
essary, you can rotate the TA diode by 90◦to best match these
elliptical beam profile of the seed laser beam.
6. The beams into and out of the TA chip are focused with aspheric
lenses mounted to wire-cut flexures. Using the flexure alignment
screws (see fig. 3.2), adjust the input collimation lens position so
that the weak alignment beam exits (from the input side of the MSA)
parallel to and aligned with the MSA. Adjust the input focus by ro-
tation of the lens mount using the focus tool provided with your
amplifier (see fig. 3.2).
Flexure alignment screwsFocus toolLens focus
Figure 3.2: TA power block, showing location of flexure screws for adusting
alignment of input and output lenses.

10 Chapter 3. MSA: internal seed alignment
7. Install the first isolator and optimise transmission to the TA. The
polarisation will not match the TA diode, and therefore a waveplate
rotator will be required between the isolator and TA. Typically the
second isolator will have a waveplate mounted inside the exit aper-
ture (see fig. 2.1) which can be temporarily installed in the first
isolator.
8. Turn on your seed laser and ensure about 15 mW of power will be
available at the amplifier input. Record the seed laser power.
9. Using mirrors M1 and M2 between the seed laser and TA, align your
seed laser beam with the amplifier alignment beam. Both beams
should be colinear and collimated. To optimise the alignment, use a
’walking’ procedure as follows.
(a) For the horizontal axis first, find the maximum output power by
adjusting the mirror closest to the amplifier (furthest from the
seed), mirror M2.
(b) Take note of the output power.
(c) Adjust the horizontal axis of the mirror furthest from the am-
plifier (closest to the seed, mirror M1) clockwise such that the
output power drops by no more than 25%. Take note of roughly
how many degrees rotation were required.
(d) Adjust the horizontal axis of mirror M2 and maximise for ampli-
fier output power. Compare the new maximum amplifier output
power you have obtained to the output power photocurrent you
obtained at step (b).
(e) If your new power is greater, repeat steps (c) and (d). If your
new power is lower, adjust the horizontal axis of mirror M1 anti-
clockwise to return it to its original angle (as you noted at the
end of step (c)), then optimise the horizontal axis of mirror M2
to regain the output power you noted in step (b). If your first
horizontal clockwise adjustment of both mirrors (steps (b) and
(c)) resulted in a decrease in output power, repeat steps (c) and
(d) using an anti-clockwise adjustment instead.