THORLABS DMH40-F01 User manual

Piezoelectric Deformable Mirror
2021
DMH40(/M)-F01,
DMH40(/M)-P01
Operation Manual

Version:
Date: 1.1 15-Apr-2021
Copyright © 2021 Thorlabs

Foreword
Contents
1 General Information 1
11.1 Ordering Codes and Accessories
21.2 Requirements
21.2.1 Software Requirements
21.2.2 Hardware Requirements
2 Operating Principle 3
32.1 Mirror
52.2 Segment Structure
62.3 Closed Loop Control
82.4 Hysteresis of Piezoelectric Materials
92.5 Creep of Piezoelectric Materials
122.6 Relaxing the Mirror
3 Getting Started 13
133.1 Parts List
4 Operation 14
144.1 Operating Elements
144.2 Installing Software
154.3 Mounting
154.4 First Steps
164.5 Out-of-the-Box Test
174.6 Software Deformable Mirror
174.6.1 GUI Header
184.6.2 Menu Bar
214.6.3 Toolbar
224.6.4 Common Settings
234.6.5 Display Mirror Control
244.6.5.1 Individual Segment Control
244.6.5.2 Control in Arbitrary Groups of Segments
254.6.6 Control Panel
254.6.6.1 Zernike Control
274.6.6.2 Mirror Manipulation
284.6.6.3 Control Loop Settings
294.6.7 Color Bar
304.6.8 Status Bar
314.6.9 Display Mirror Temperature
324.6.10 The Configuration File
334.7 Closed Loop Control

5 Write Your Own Application 34
375.1 Instrument driver 32bit on 32bit systems
385.2 Instrument driver 32bit on 64bit systems
405.3 Instrument driver 64bit on 64bit systems
6 Maintenance and Service 41
416.1 Version Information
436.2 Troubleshooting
7 Appendix 46
467.1 Technical Data
497.2 Analog Feedback Connector
507.3 About Zernikes
517.4 Dimensions DMH40-xxx (Imperial)
527.5 Dimensions DMH40/M-xxx (Metric)
527.6 Safety
537.7 Return of Devices
547.8 Certifications and Compliances
557.9 Warranty
557.10Copyright and Exclusion of Liability
567.11References
577.12Manufacturer Address
587.13Thorlabs Worldwide Contacts and WEEE policy

© 2021 Thorlabs
We aim to develop and produce the best solutions for your
applications in the field of optical measurement techniques. To help
us to live up to your expectations and constantly improve our
products, we need your ideas and suggestions. We and our
international partners are looking forward to hearing from you.
Thorlabs GmbH
Warning
Sections marked by this symbol explain dangers that might result in
personal injury or death. Always read the associated information
carefully before performing the indicated procedure.
Please read this advice carefully!
This manual also contains "NOTES" and "HINTS" written in this form.
Attention
Paragraphs preceded by this symbol explain hazards that could
damage the instrument and the connected equipment or may cause
loss of data.
Note

© 2021 Thorlabs1
DMH40
1 General Information
The Thorlabs' Piezoelectric Deformable Mirror DMH40 is used to correct distorted wavefronts
that result from common sources of wavefront aberrations, such as astigmatism and coma.
The Thorlabs DMH40 Deformable Mirror consists of a piezoelectric disk with a segmented back
electrode glued to a glass substrate carrying the continuous reflective surface. The segmented
back electrode controls a number of independent mirror segments. Each segment area can be
forced to perform a local concave or convex bending, depending on the applied voltage.
Thereby the mirror can assume any desired shape to compensate for distorted wavefronts.
Besides individual or grouped segment control, the Thorlabs Deformable Mirror software
provides pre-defined voltage patterns for generation of Zernike function shapes. An adaptive
control algorithm based on these Zernike coefficients allows closed loop operation in conjunc-
tion with a feedback signal from our Shack-Hartmann wavefront sensors.
Each DMH40 deformable mirror has a Ø14 mm pupil and is available with one of two optical
coatings: UV-Enhanced Aluminum for 250 nm to 450 nm wavelength or Protected Silver for 450
nm to 20 mm wavelength.
Compared to the Thorlabs deformable mirror DMP40, the DMH40 has a more than 2 fold larger
stroke (hoisting capacity) resulting in a more than 2 fold curvature of the mirror. While, the
DMP40 can tilt the mirror due to its outer arms, the DMH40 can be tilted by using a kinematic
mount.
Attention
Please find all safety information and warnings concerning this product in the chapter Safety
in the Appendix.
1.1 Ordering Codes and Accessories
Item#
Short Description
DMH40-F01
Piezoelectric Deformable Mirror, UV-Enhanced Aluminum, 14 mm Pupil Dia-
meter, Imperial
DMH40/M-F01
Piezoelectric Deformable Mirror, UV-Enhanced Aluminum, 14 mm Pupil Dia-
meter, Metric
DMH40-P01
Piezoelectric Deformable Mirror, Protected Silver, 14 mm Pupil Diameter, Im-
perial
DMH40/M-P01
Piezoelectric Deformable Mirror, Protected Silver, 14 mm Pupil Diameter,
Metric
Recommended Accessories:
For Closed Loop Control setups, we recommend Thorlabs Wavefront Sensors (WFS) and Mi-
crolens Arrays (MLA) that are offered in combination.
Wavefront Sensor
(WFS Item# Prefix)
Short description
WFS20
High Speed Shack-Hartmann Wavefront Sensor
WFS30
General Purpose Shack-Hartmann Wavefront Sensor
WFS40
Large Area Shack-Hartmann Wavefront Sensor
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1 General Information
2
Microlens Arrays:
Microlens Arrays
(WFS Item# Suffix)
Short description
-5C
based on Thorlabs MLA150-5C
-7AR
based on Thorlabs MLA150-7AR
-14AR
based on Thorlabs MLA300-14AR
1.2 Requirements
These are the requirements for the PC intended to be used for operation of the DMH40.
1.2.1 Software Requirements
The Thorlabs Deformable Mirror software is compatible with the following operating systems:
·Windows®7 SP1 and later (32-bit, 64-bit)
·Windows®8.1 (32-bit, 64-bit)
·Windows®10 (32-bit, 64-bit)
For operation of the DMH40, Microsoft®.Net Framework version 4.6.2 or higher must also be
installed. This software comes with the Thorlabs Deformable Mirror software installation pack-
age, available for download on the software tab of the Piezoelectric Deformable Mirror website.
For the Control Loop operation a Thorlabs Wavefront Sensor with a software version of 5.0
and later is required. For optimal performance, please use the latest software version available
online.
1.2.2 Hardware Requirements
CPU: 2 GHz or higher
RAM: 4 GB
Graphic card: 256 MB memory (shared)
Graphic resolution: min.: 1024 x 768; recommended: 1280 x 800
Hard disk: 1.2 GB (32 bit) / 2.6 GB (64 bit) free storage space
Interface: USB 2.0 port, USB cable according the USB 2.0 specification
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DMH40
2 Operating Principle
DMH40 structure - rear view
showing 40 mirror segments
The heart of the Thorlabs DMH40 is a deformable mirror. It is comprised of a glass substrate
with a reflective coating that has a thin piezo ceramic disk with segmented electrodes glued to
the back side.
The mirror is mounted via 3 mounting joints shown above.
2.1 Mirror
Cross section of the DMH40 inner mirror
The above sketch shows a simplified cross section of the inner mirror. The common electrode
for all segments is connected to ground (0 V), while the back side electrode is divided into 40
single segments that can be controlled individually by a DC voltage in the range 0 – 300 V
each.

© 2021 Thorlabs
2 Operating Principle
4
During the gluing process, a control voltage of 150 V is applied to all segment electrodes. For
this reason, a flat mirror surface will appear at a control voltage level of 150 V, applied to all
segments. At voltages <150 V, the piezo material above the corresponding electrode will ex-
pand, leading to a local concave shape, while a voltage >150 V shrinks the piezo and leads to a
local convex shape:
Applying a voltage to a piezo segment
Applying the same voltage higher or lower than 150 V to all 40 electrodes results in a pure
spherical mirror shape. An arbitrary surface shape can be generated by applying a defined
voltage pattern.
Note
The mirror will be nearly flattened after connecting it to the power supply and to a PC with the
installed Thorlabs Deformable Mirror software! The reason is that the software will initialize the
hardware only after PC connection is made. Whenever no power is connected to the DMH40,
the mirror will be concave (0 V position).

© 2021 Thorlabs5
DMH40
2.2 Segment Structure
View onto the mirror surface
Electrode numbering is shown for a mirror with the reflective surface facing the viewer.
Note
The instrument driver software accepts zero-based segment indices in the range 0 – 39, while
the user interface in the software refers to the numbering as shown in the above diagram.
The segments 25 to 40, surrounding the mirror pupil, are used to get defined curvatures even
at the pupil's rim. This improves the quality and amplitude of the Zernike terms generation.

© 2021 Thorlabs
2 Operating Principle
6
2.3 Closed Loop Control
The Thorlabs Deformable Mirror software allows for closed loop control using a sensor and the
DMH40 to be set up in order to achieve flat, spherical, or other wavefront shapes. Basically,
there are two methods to build closed loop feedback: either by using a photo detector with the
analog feedback input of the DMH40 (1) or by using a wavefront sensor feedback loop with the
respective software solution (2).
1) Analog Feedback Loop
A part of the manipulated beam, derived from a polarization independent beam splitter, is direc-
ted via a focusing lens and a pin hole onto a photo detector (PD). The output signal of the
photo detector is connected to an Analog Feedback Connector (not included). This Analog
Feedback Connector can then be plugged into the DMH40 analog feedback input jack. The
feedback values can be used to optimize the adaptively adjusted wavefront. A simple max
search algorithm can be programmed (not included in the GUI or driver) to optimize the wave-
front without a wavefront sensor.
This feedback method works for 2 cases:
a. Flat Wavefront
If the beam focus is located exactly in the plane of the pinhole, the optical power incident on the
photo detector will be at a maximum in the case of an ideally flat wavefront.
b. Spherical Wavefront
If the focal point is located in front of or behind the pinhole, the optical power into the photo de-
tector will be maximized when the wavefront is spherical.
The analog feedback input (2.5 mm stereo jack) of the DMH40 provides two separate inputs
dedicated to voltage and current feedback signals. The current input can be connected directly
to a photodiode.
Note
There is no internal calibration for the current and voltage values. These are just feedback val-
ues that are suited for maximum search algorithms but not for exact measurements!
2) Wavefront Sensor Feedback Loop
Using the measurement results of a Thorlabs Wavefront Sensor, the Thorlabs Deformable Mir-
ror software can control the wavefront reflected from the DMH40 according to the settings. This
way it is possible to generate a flat wavefront.
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DMH40
The Thorlabs Deformable Mirror software uses the wavefront sensor measurement data
provided via the WFS DataSocket interface (included with the Thorlabs Wavefront Sensor soft-
ware).
In the section Closed Loop Control of this manual, this control loop method is described.
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© 2021 Thorlabs
2 Operating Principle
8
2.4 Hysteresis of Piezoelectric Materials
Hysteresis is a well known effect in ferromagnetic and ferroelectric materials.
Due to the hysteresis of the PZT (lead zirconate titanate) material used for the Deformable Mir-
ror, the mirror stroke depends not only on the actual applied control voltages, but also on the
"history" of recent changes. This "memory effect" is caused by internal states of the material
that differ for increasing and decreasing voltages.
Due to the hysteresis effect, the mirror stroke does not follow the same track each time the con-
trol voltage is increased or decreased. The diagram below shows a typical hysteresis curve of
the spherical deformation at a voltage oscillation between 0 V and 300 V (i.e., the same voltage
change is applied to all 40 mirror segments).
DMH40 Hysteresis Curve
The hysteresis is expressed as the maximum difference divided by the maximum stroke
between the two tracks. For this particular sample the hysteresis is 3.5 µm or 14% related to
the total stroke range of 24.5 µm. The max hysteresis of the used material for the DMH40 is
25%.
For this reason, a control voltage of 150 V (half of the maximum control voltage) will not always
produce a flat mirror (zero spherical deformation); the previous control voltage needs to be
taken into account. For instance, a flat shape is achieved when the voltage is increased from
0V towards 171V and the same shape is achieved when decreasing the voltage from 300V
down to 123V.
Note
The maximum concave and the maximum convex stroke may differ slightly as well!
Hysteresis Compensation
The Thorlabs Deformable Mirror software incorporates a hysteresis compensation. The driver
software monitors all consecutive voltage changes for each segment individually and applies a
corrected voltage, calculated based on a mathematical algorithm, to the mirror segments.
Consequently, when controlling the DMH40 via the Thorlabs Deformable Mirror software, the
mirror behaves almost like a mirror without a hysteresis effect. Both tracks of the hysteresis
curve will collapse to a straight line.

© 2021 Thorlabs9
DMH40
2.5 Creep of Piezoelectric Materials
The creep effect is known in material science as a slow movement or deformation of a material
under the influence of an external stress.
In piezoelectric materials, a creep effect is considered the continuing material expansion or
shrinking after a voltage change was applied. The creep effect lets the piezoelectric material
continue its mechanical change in the same direction as was induced by the last voltage step.
The resulting stroke change is logarithmically dependent on time, which means that the creep
speed decreases over the time, but never actually ceases.
After power-on, all DMH40 control voltages are set to 150V in order to get a nearly flat shape.
Since the piezo material was at zero voltage for a long time before, the voltage step from 0 to
150V causes an immediate jump, followed by a long-term drift.
Drift after Power-On (Linear Time Scale)
The majority of the creep is observed within half an hour but it goes on over many hours. In log-
arithmic scale the drift appears as a nearly straight line:
Drift after Power-On (Logarithmic Time Scale)

© 2021 Thorlabs
2 Operating Principle
10
Relaxing the Creep
The Thorlabs Deformable Mirror software offers a Relax function. By pressing the appropri-
ate button, the control voltages of all segments are increased and decreased sequentially, start-
ing at the full range (0 to 300 V) with subsequent decreasing amplitude, reaching at the end the
mean voltage of 150 V. This way the time required to come to a stable and nearly flat mirror
shape is shortened drastically.
Drift effects occur whenever the mirror’s control voltage is changed. For instance, a step from
150V to 300V on all segments causes a step from zero to about 11.3 µm spherical amplitude.
Drift after 150 V -> 300 V Step (Short Term)
Although this 11.3 µm deflection seems to be stable after a few minutes, there is a long-term
drift towards 13.2 µm after 10 hours:
Drift after 150 V -> 300 V Step (Long Term)
12

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DMH40
Creep Consequences
Consider the creep effect particularly when performing adaptive correction using a feedback
loop control: As long as the control loop is closed, slow drift effects of the DMH40 are corrected
automatically.
As soon as the loop control is stopped, the last voltage pattern remains applied to the mirror
segments, but the physical mirror shape will start a slow, continuous creep which leads to a
wavefront drift.
Note
Even if a voltage pattern that produced a defined wavefront is reproduced exactly, the original
defined wavefront will not be reproduced exactly.
The Thorlabs Deformable Mirror software is not able to compensate for the creep effect. Creep-
ing can be eliminated only within a closed loop control system. In other words, piezoelectric de-
formable mirrors cannot be used to exactly set a deterministic wavefront distortion.
Shift of Hysteresis Curve
Finally, the creep overlays the hysteresis, so that the hysteresis curve will be shifted, depending
on the voltage applied to all segments before measuring the hysteresis curve. The diagram be-
low illustrates that.
Shift of Hysteresis Curve
The creep effect is present regardless of whether the DMH40 is switched on or off. After the
DMH40 was switched-off for a long period, the hysteresis was measured. The creep let the mir-
ror’s concave shape at 0 V increase, which leads to a shift of the hysteresis curve downwards
(blue curve).
Then a segment voltage of 300 V was applied for several hours. The hysteresis (red curve) is
shifted by about 2.1 µm towards convex direction, equivalent to about 8% of the spherical
range.
However, both hysteresis amplitudes are equal, they are just shifted.

© 2021 Thorlabs
2 Operating Principle
12
2.6 Relaxing the Mirror
In the previous, chapters some essential properties of piezoelectric materials - hysteresis and
creep (drift) - were described. These properties have a non-negligible impact on the control of
the mirror surface by applying voltages. The resulting surface shape depends not only on the
present voltage pattern, but also on the "history" of previous changes.
Example: Assume a starting condition where the mirror was flat at 150 V:
1. The segment voltage has been changed from 150 V to 300 V (maximum convexity), and
then back to 150 V.
In this case, the hysteresis' impact is that after applying 150 V the mirror remains some-
what convex. The creep effect, on the other hand, makes the surface continue to move in
the direction of the last adjustment: the mirror surface becomes more and more flat. If we
wait long enough, it will become concave.
2. The segment voltage has been changed from 150V to 0V (maximum concavity) and then
back to 150V.
This is the opposite case: The mirror remains slightly concave due to hysteresis, and con-
tinues to flatten over time due to creep.
The effects described above are more significant, the larger the change in the applied voltage.
The Thorlabs Deformable Mirror software provides a Relax feature to eliminate or at least to
minimize the above impacts. It will carry out 3 steps:
1. Remember the actual voltage pattern
2. Damped oscillation of the applied voltage symmetrically with respect to the original voltage.
This means that to a segment with an initial voltage of 150V a "sequence" of 300 V - 0 V -
285 V - 15 V -... 165 V - 145 V - 150V will be applied during relax. This maximum relax
amplitude will be the less the closer the initial segment voltage was to the limit (0 V or 300
V).
3. Restore the voltage pattern that was present prior to Relax
This way, the mirror is moved in both directions with decreasing amplitude so that hysteresis
and creep (drift) effects will be minimized.
When should the Relax be done?
Relax is recommended to prevent recently-made large voltage changes from impacting the next
experiment, e.g.:
·after starting up the software
·after applying voltage patterns and their subsequent restoration
·prior to a new experiment
·prior to starting closed loop control using a wave front sensor
How to Relax segments
To relax the mirror segment, click the 'Relax' button in the tool bar.
An appropriate tool tip appears when hovering the mouse over the the the 'Relax' button.
8

© 2021 Thorlabs13
DMH40
3 Getting Started
Inspect the shipping container for damage. When opening the package, please do not cut
through the cardboard.You might need the box for storage or for returns.
If the shipping container seems to be damaged, keep it until you have inspected the contents
and you have inspected the DMH40 mechanically and electrically. Keep the container for stor-
age or in order to return the product in case of future problems.
Verify that you have received the following items within the package:
3.1 Parts List
1. DMH40 or DMH40/M Deformable Mirror
2. SM2CP1 threaded cap
3. USB 2.0 cable A to Mini B, length 1.5 m
4. Power supply 100 to 240 V AC to 12 V / 1.5A DC
5. Power Cord
6. Quick Reference

© 2021 Thorlabs
4 Operation
14
4 Operation
4.1 Operating Elements
4.2 Installing Software
Note
Do not connect the DMH40 to the PC prior to software installation!
Attention
Exit all running applications on your PC as the installer may require a reboot of your PC during
installation!
Software download
Please download the software package from the software tab of the product website. The most
recent version of the software will always be available online.
Click the Software button to download the DMH40 Software ZIP archive, unpack it and open
the installation folder. Double click the application setup.exe.
Note
Depending on your Windows®Security and User Account Control settings, warnings may ap-
pear several times during the installation process, asking to allow software installation. Please
confirm that when appropriate in order to proceed with a proper software installation.
The installer checks if Microsoft®.NET Framework 4.6.2 is installed already and requires the in-
stallation of eventually missing components. An appropriate status message appears - click "In-
stall".
Usually, the Microsoft®.NET Framework is already installed and updated during the Windows®
Update process. After finishing the .Net Framework installation, the installer may require a re-
boot of the computer. Please do so.
After the reboot, the installer continues with installing the DMH40 software.
A Readme screen comes up with important information about the installed software.
Click Next > and in the next screen Finish to finalize installation process.

© 2021 Thorlabs15
DMH40
4.3 Mounting
Mounting the DMH40
The imperial version DMH40 and metric version DMH40/M each feature two different threads
for mounting of the deformable mirror on a post.
To mount the DMH40, please use either a post with a 1/4-20 or 8-32 threaded setscrew, 6 mm
in length.
To mount the DMH40/M, please use either a post with a M6 x 1 or M4 x 0.7 threaded setscrew,
6 mm in length.
Mounting Optics on the DMH40
The SM2 external thread allows mounting of appropriate mounting optics or lens tubes.
To mount a Thorlabs 30 mm cage system, both DMH40 and DMH40/M offer four 4-40 inner
threads with 5 mm depth on the front of the device.
4.4 First Steps
After installing the Thorlabs Deformable Mirror software and mounting the DMH40 to the optical
setup, proceed with the following steps:
1. Connect the power supply to the mains outlet using the provided power cord.
2. Connect the DC output of the power supply to the DC input (4).
3. Connect the USB cable to the DMH40 and to the PC. Make sure the status LED (3) lights
up, first red (no DC input recognized) and finally green (ready).
4. The operating system recognizes the connected DMH40 and installs necessary software
components (device driver).
5. Start the DMH40 software from the desktop icon.
6. The application starts and automatically connects to the DMH40.
7. A warning screen may appear: DataSocket Error: