MOGlabs DLC202 User manual

External Cavity Diode Laser Controller
Models DLC-202, DLC-252, DLC-502
Revision 6.00

Limitation of Liability
MOG Laboratories Pty Ltd (MOGlabs) does not assume any liabil-
ity arising 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) 2010. No part
of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical,
photocopying or otherwise, without the prior written permission of
MOGlabs.
Contact
For further information, please contact:
MOG Laboratories Pty Ltd
420 Victoria St
Brunswick VIC 3056
AUSTRALIA
Tel: [phone]
Fax: [phone]
Email: [email protected]
Web: www.moglabs.com

Preface
Diode lasers can be wonderful things: they are efficient, compact,
low cost, high power, low noise, tunable, and cover a large range
of wavelengths. They can also be obstreperous, sensitive, and tem-
peramental, particularly external cavity diode lasers (ECDLs). The
mechanics and optics needed to turn a simple $10 120 mW AlGaAs
diode laser into a research-quality narrow-linewidth tunable laser
are fairly straightforward [1, 2, 3, 4], but the electronics is demanding
– and, until now, not available commercially from a single supplier,
let alone in a single unit.
The MOGlabs range of ECDL controllers change that. With each DLC
unit, we provide everything you need to run your ECDL, and lock it
to an atomic transition. In addition to current and temperature con-
trollers, we provide piezo drivers, sweep ramp generator, modulator
for AC locking, lock-in amplifier, feedback servo system, laser-head
electronics protection board, even a high-speed low-noise balanced
photodetector.
We would like to thank the many people that have contributed their
hard work, ideas, and inspiration, especially Lincoln Turner, Karl
Weber, and Jamie White, as well as those involved in previous con-
troller designs, in particular Mirek Walkiewicz and Phillip Fox.
We hope that you enjoy using the DLC as much as we do. Please let
us know if you have any suggestions for improvement in the DLC or
in this document, so that we can make life in the laser lab easier for
all, and check our website from time to time for updated information.
Robert Scholten and Alex Slavec
MOGlabs, Melbourne, Australia
www.moglabs.com
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ii

Safety Precautions
Please note several specific and unusual cautionary notes before
using the MOGlabs DLC, in addition to the safety precautions that
are standard for any electronic equipment or for laser-related in-
strumentation.
WARNING The rear-panel connector for the laser is similar to standard
DVI (Digital Video Interface) plugs as used for consumer digi-
tal display devices. The pins on this connector can be at high
potential (up to 150 V). These can be hazardous to life and
should be protected by connection of the correct cable to the
laser. Under no circumstances should a standard DVI device
such as an LCD display be connected to this socket!
CAUTION Please ensure that the unit is configured for the correct voltage
for your AC mains supply before connecting. The supply must
include a good ground connection.
WARNING The internal circuit boards and many of the mounted compo-
nents are at high voltage, with exposed conductors, in partic-
ular the high-voltage piezo driver circuitry. The unit should
not be operated with covers removed.
WARNING If using a Zeeman coil modulator as described in appendix C,
the secondary potential can easily be hundreds of volts. Please
ensure that your coil and balance capacitor do not have ex-
posed connections, and that all components have sufficient
voltage rating.
NOTE The MOGlabs DLC is designed for use in scientific research
laboratories. It should not be used for consumer or medical
applications.
iii

Protection Features
The MOGlabs DLC includes a number of features to protect you and
your laser.
Softstart A time delay followed by linearly ramping the diode current;
total of 2.5 s.
Circuit shutdown Many areas of the circuitry are powered down when not in use.
The high voltage supply and piezo drivers, the diode current
supplies, the coil driver, and others are without power when
the unit is in standby mode, if an interlock is open, or a fault
condition is detected.
Current limit Sets a maximum possible diode injection current, for all op-
erating modes. Note that current supplied through the RF
connector on the laser headboard is not limited.
Cable continuity If the laser is disconnected, the system will switch to standby
and disable all laser and piezo power supplies. If the laser
diode, TEC or temperature sensor fail and become open-circuit,
they will be disabled accordingly.
Short circuit If the laser diode, TEC or temperature sensor fail and become
short-circuit, or if the TEC polarity is reversed, they will be
disabled accordingly.
Temperature If the detected temperature is below −5◦C or above 35◦C, the
temperature controller is disabled.
Internal supplies If any of the internal DC power supplies (+5,±10,±12 V) is
1 V or more below its nominal value, the respective components
(temperature controller, diode current supply) are disabled.
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v
Protection relay When the power is off, or if the laser is off, the laser diode
is shorted via a normally-closed solid-state relay at the laser
head board.
Laser LED Bright white LED illuminates when laser is switched on.
Mains filter Protection against mains transients.
Key-operated The laser cannot be powered unless the key-operated STANDBY
switch is in the RUN position, to enable protection against
unauthorised or accidental use.
Interlocks Both the main unit and the laser head board have interlocks,
to allow disabling of the laser via a remote switch, or a switch
on the laser cover.

RoHS Certification of
Conformance
MOG Laboratories Pty Ltd certifies that the MOGlabs Diode Laser
Controller (Revision 3) is RoHS-5 compliant. MOG Laboratories
notes, however, that the product does not fall under the scope defined
in RoHS Directive 2002/95/EC, and is not subject to compliance, in
accordance with DIRECTIVE 2002/95/EC Out of Scope; Electron-
ics related; Intended application is for Monitoring and Control or
Medical Instrumentation.
MOG Laboratories Pty Ltd makes no claims or inferences of the
compliance status of its products if used other than for their intended
purpose.
vi

Contents
Preface i
Safety Precautions iii
Protection Features iv
RoHS Certification of Conformance vi
1 Introduction 1
1.1 Simplest configuration . . . . . . . . . . . . . . . . . . 1
1.2 Passive frequency control . . . . . . . . . . . . . . . . 2
1.3 DC locking to an atomic transition . . . . . . . . . . . 3
1.4 AC locking to an atomic transition . . . . . . . . . . . 4
2 Connections and controls 7
2.1 Front panel controls . . . . . . . . . . . . . . . . . . . 7
2.2 Front panel display/monitor . . . . . . . . . . . . . . . 10
2.3 Rear panel controls and connections . . . . . . . . . . 12
2.4 Internal switches and adjustments . . . . . . . . . . . 14
3 Operation 21
3.1 Simplest configuration . . . . . . . . . . . . . . . . . . 21
3.2 Laser frequency control . . . . . . . . . . . . . . . . . 22
3.3 External scan control . . . . . . . . . . . . . . . . . . . 24
3.4 Locking to an atomic transition: DC .......... 24
3.5 Locking to an atomic transition: AC .......... 27
3.6 Locking using an external signal . . . . . . . . . . . . 30
3.7 External control of lock frequency setpoint . . . . . . 31
4 Optimisation 33
4.1 Frequency reference . . . . . . . . . . . . . . . . . . . 33
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viii Contents
4.2 Noisespectra....................... 35
A Specifications 37
A.1 RF response ........................ 41
A.2 Sweep saturation and trigger . . . . . . . . . . . . . . 41
B Troubleshooting 43
B.1 STANDBY/RUN indicator ................. 43
B.2 Diode OFF/ON indicator................. 44
B.3 Locking........................... 45
C Modulation coils 47
C.1 Field requirements . . . . . . . . . . . . . . . . . . . . 47
C.2 Coilimpedance ...................... 48
C.3 Impedance matching . . . . . . . . . . . . . . . . . . . 49
C.4 Tuning ........................... 50
C.5 Shielding ......................... 51
D External modulators and injection current modulation 53
D.1 Coupling circuit . . . . . . . . . . . . . . . . . . . . . . 53
D.2 Injection current modulation . . . . . . . . . . . . . . . 54
E Photodetector 57
E.1 Photodiodes........................ 58
F Laser head board 59
F.1 Headboard connectors . . . . . . . . . . . . . . . . . . 59
F.2 Grating pivot point compensation . . . . . . . . . . . 60
F.3 RFcoupling........................ 61
G Connector pinouts 63
G.1 Photodetector....................... 63
G.2 Laser............................ 63
G.3 Interlock .......................... 64
G.4 Digitalcontrol....................... 65
H PCB layout 67
References 70