AOS Hartmann User manual

Version 1.0 –10/2/12
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2021 Girard Blvd. Suite 150
Albuquerque, NM 87106
[phone] x184
www.aos-llc.com
Hartmann Sensor
Manual

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Table of Contents
1Introduction............................................................................................................................. 3
1.1 Device Operation.............................................................................................................. 3
1.2 Limitations of Hartmann Sensing .................................................................................... 3
2Quick-Start Installation Guide................................................................................................ 4
3General Wavefront Sensor Usage........................................................................................... 4
3.1 Warnings and Usage Advice............................................................................................ 4
3.2 Typical Hartmann Sensor Use –Quick Start Guide ........................................................ 5
3.2.1 Comments about Reference/Calibration Files.......................................................... 5
3.2.2 Alignment to an Absolute Reference........................................................................ 5
3.2.3 Creating a Relative Reference .................................................................................. 6
3.2.4 Making Wavefront Measurements............................................................................ 6
4Comments on Specific Hartmann Wavefront Sensors............................................................ 6
4.1 Firewire Wavefront Sensors............................................................................................ 6
4.1.1 Power ........................................................................................................................ 6
4.2 GigE Wavefront Sensors.................................................................................................. 7
4.2.1 Power ........................................................................................................................ 7
4.3 SU320KTSW-1.7RT IR Wavefront Sensor..................................................................... 7
4.3.1 Mechanical Drawing................................................................................................. 7
5Software.................................................................................................................................. 9
6Appendix: Select Camera Parameters Summary.................................................................... 9
7Appendix: Discontinued Sensor Information ....................................................................... 10
7.1 USB Webcam Hartmann Sensors (discontinued) .......................................................... 10
7.1.1 General Installation Notes: ..................................................................................... 10
7.1.2 Warnings:................................................................................................................ 10
7.2 Fire-I Webcam Firewire Wavefront Sensors (discontinued) ......................................... 11
7.2.1 Instructions and Warnings ...................................................................................... 11
7.2.2 Mounting................................................................................................................. 11
7.2.3 Package Dimensions............................................................................................... 12

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1 Introduction
The Hartmann wavefront sensor was developed in 1904 by J. Hartmann to do optical metrology
of large optics. Hartmann’s original sensor was fabricated by combining a plate with an array of
holes and photographic film. Electronic imagers replaced the photographic film. In 1971
Roland Shack suggested using a lens array instead of the array of holes for better optical
efficiency, thereby creating the Shack-Hartmann wavefront sensor. The modern Hartmann
sensor consists of a lens array (Shack-Hartmann) or an aperture array (Hartmann) in front of an
electronic (CCD or CMOS) imager.
The Hartmann sensor described here consists of an aperture array mounted in front of a
commercially available web camera. This manual will begin by describing the operation of a
general Hartmann sensor. Then the installation will be described. Finally the operation of the
software will be described.
1.1 Device Operation
A beam of light illuminating a Hartmann sensor is divided into pieces by the sub-apertures of the
aperture array. The position of each spot diffracted from the apertures is directly proportional to
the average wavefront slope. Wavefront slope measurements are made differentially by
comparing the position of the diffracted spots on the
sensor with those measured for a reference wavefront.
The ratio of the motion of the spot position in both
axes to the distance between the aperture array and the
imager is the gradient of the wavefront. The
wavefront can be reconstructed by integrating the
measured wavefront gradient.
Figure 1.1.1 shows an example of a reference
wavefront, shown in green, superimposed on a
wavefront being measured (blue) in 1D. The dotted
lines show the wavefront impinging on the aperture
array. The motion of the spots is directly proportional
to the average slope over the sub-apertures.
1.2 Limitations of Hartmann Sensing
Hartmann sensing is a very powerful technique for measuring both intensity and phase
simultaneously, but it has some limitations. The spatial resolution of a Hartmann sensor is
inherently lower than the underlying imager because accurate spot determination requires an
array of camera pixels. The temporal resolution of a Hartmann sensor is typically limited by the
camera frame rate, but can be also limited by the image processing required to create a wavefront
or wavefront slope from the image.
The slope measurement accuracy of a Hartmann sensor is limited to its ability to determine the
spot position accurately. There are several things that impact the accuracy of this measurement.
Spot position determination is typically done using centroiding or taking the first moment of the
spot. This accuracy of this measurement is proportional to the number of bits of resolution in the
Figure 1.1.1 - Reference wavefront
(green) and measurement wavefront
(blue).

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intensity measurement and the number of pixels being illuminated, but is typically accurate to
around 1/10th of a pixel size. Averaging over many frames can be used to increase the
resolution, but only by the square root of the number of averages. Another thing that impacts
spot position determination accuracy is structure on the intensity pattern illuminating a sub-
aperture. This effect can be mitigated to some extent by moving from an aperture array to a lens
array (Shack-Hartmann wavefront sensing), but there will always be coupling between the
intensity variations and the spatial variation of the slope. In the case where there is significant
variation in the wavefront slope and the intensity over a sub-aperture, the Hartmann sensor can
be thought of as measuring a weighted-average of the wavefront slope over that sub-aperture.
2 Quick-Start Installation Guide
Install the AOS software.
Plug in the camera.
Set it up to be properly illuminated.
Run the AOS Adaptive Optics software.
3 General Wavefront Sensor Usage
3.1 Warnings and Usage Advice
Cleaning: The Hartmann array is not designed to be cleaned. It can be sprayed gently
with pressurized air to remove dust, but aggressive cleaning will damage the device.
Damage induced by cleaning will void the warranty.
Mounting: Each device has specific mounting suggestions below. It is not
recommended to mount the wavefront sensor using the beam tube at the front-end of the
camera.
Saturation: It is very important to avoid saturating the camera during operation.
Saturation can result in inaccurate measurements. There is some ability for the user to
control the gain and exposure interval in software, but in extreme cases, this will have to
be addressed in hardware via absorbing neutral density filters. Do not use reflecting
neutral density filters! They will cause the Hartmann spots to be corrupted such that an
accurate measurement cannot be made.
Slope Dynamic Range: The Hartmann sensor has a certain range of slopes over which it
can accurately measure. The maximum dynamic range is obtained when the edge of the
focal spots reach the edge of the areas of interest (AOIs). Beyond this point, the
Hartmann sensor cannot accurately measure the slopes without heroic processing.
Camera Parameters: Each Hartmann sensor has a set of parameters obtained during
calibration of the device. It is important to make sure that these parameters are used
during the operation of the device.
Imaging: When imaging onto the wavefront sensor, plan on creating the image on the
lens/Hartmann array, not on the image sensor itself.
Non-English Windows Operating Systems: The software is designed for US English
Windows Operating Systems. Many of the data files for the AOS software use comma
separated values (CSV) with decimal numbers. Some foreign operating systems switch
the characters such that commas and periods mean different things. If using a foreign

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operating system, the meaning of commas and periods in numeric values may need to be
switched before the software will operate properly.
3.2 Typical Hartmann Sensor Use –Quick Start Guide
Hartmann sensors measure the differential tilt between two images. When using a Hartmann
sensor, the reference can be taken by the user or can be that provided by AOS. The next section
describes how to align a Hartmann sensor to an absolute reference file. The following section
describes how to create a relative reference file and use the AOS Hartmann Wavefront Sensor
(HWFS).
3.2.1 Comments about Reference/Calibration Files
Upon startup the software tries to load the calibration data in a file called defaultCal.txt. If this
file does not exist, the user gets a warning message and the sensor loads without any calibration
data. The user can overwrite the existing defaultCal.txt file with a new calibration file at any
time by deleting the old file and renaming the new calibration file to defaultCal.txt. The user can
load a calibration file at any time using the File-Open-Calibration menu option. The terms
reference and calibration as will be used interchangeably throughout this manual.
3.2.2 Alignment to an Absolute Reference
The reference image provided by AOS is taken under relatively uniform illumination of a planar
wavefront. When using the AOS reference (also referred to as the absolute reference), it is
critical to align the sensor to that reference. To facilitate this, the wavefront sensor needs to be
mounted on a kinematic stage that allows the sensor to be tilted in the two axes perpendicular to
the beam propagation direction. There are several different ways of creating a mount like this.
Figure 7.1.1 shows an AOS Hartmann Sensor attached to a ThorLabs KM100P Kinematic Prism
Mount in such a way as to enable both of these axes to be manipulated. Unfortunately, the
mount shown here does not allow the sensor angle to be manipulated independent of motion the
sensor relative to the optical axis, but for fine tuning the sensor position it is effective.
The procedure for aligning the HWFS an absolute reference is:
1. Align the sensor by eye so that it is normal to the incident beam.
2. Launch the HWFS software.
3. Load the absolute reference (calibration) file.
4. Turn off tilt removal in the Setup Tab.
5. Begin acquisition in continuous mode.
6. Adjust the two tilt axes to minimize the
tilt by looking at the wavefront
amplitude in the Wavefront Display
Window, tilt amplitude in the Slopes
Display Window, or rms tilt amplitude
in the Analysis Tab.
With this procedure, it is possible to align the
sensor such that the tilt is off by exactly one
dynamic range of the wavefront sensor. The
only way of determining this is to compare the
reference image and the measured image on the
Figure 3.2.1 - Illustration of how a tilted
wavefront (blue) can be exactly one slope
dynamic range away from the reference
wavefront (green)

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HWFS. The corner sub-apertures of the AOS HWFS are not well illuminated due to the limited
size of the Hartmann screen clear aperture, so a user can look at these corner sub-apertures to
determine if the HWFS is well aligned to the beam. The corner sub-apertures should be equally
illuminated when the beam is larger than the Hartmann sensor. If they are not, adjust the angle
of the camera to make the corners look equally illuminated and repeat the alignment procedure
above.
3.2.3 Creating a Relative Reference
A differential measurement is commonly used when trying to determine the effect of a change to
an optical system. Examples include trying to measure the effect of moving a lens or the effect
of a deformable mirror on the wavefront. To make a differential measurement, it is unnecessary
to align the HWFS to an absolute reference file. Instead, a relative reference file can be created
by acquiring an image and pressing the Create Reference button. When the image is acquired,
the HWFS software automatically assumes that the user wants to analyze that image relative to
the existing calibration/reference data. With a new setup these results are often not very
meaningful and should be ignored until a valid calibration can be obtained.
3.2.4 Making Wavefront Measurements
After a valid reference is established, the wavefront sensor can be used to make wavefront
measurements. Assuming that the setup is valid, this can be accomplished using the Acquire or
Continuous Acquire buttons. There is more detail on the setup below, but the most important
things to get correct is the separation between the Hartmann array and the imaging sensor and the
pixel size. These will be set properly and stored in a reference file for your sensor that is
provided by AOS. Each sensor will have a different separation value since they are hand
assembled, so make sure this is correct before making measurements.
4 Comments on Specific Hartmann Wavefront Sensors
4.1 Firewire Wavefront Sensors
The AOS software is compatible with all the Firewire
cameras manufactured by Allied Vision Technologies
(AVT). These cameras have proven to be robust and
easy to use, but do require a 1394 Firewire port on the
computer. Since these ports are becoming less
common, we are directing more of our customers to
GigE cameras.
4.1.1 Power
Our Firewire wavefront sensors require power from
the Firewire port or power being applied to the
camera directly. Figure 3.2.1 shows the 4-pin and 6-
pin connectors for the Firewire A standard. The 4-pin
Firewire adapters that are on most laptop computers
do not provide power, so the cameras will not work
Figure 3.2.1 –Images of 6-pin and 4-pin
firewire connectors

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using only this connector. Most laptop PC-card or PCMCIA cards that provide a 6-pin interface
to Firewire do not provide power without application of that power over an external connector.
We only recommend using a 6-pin desktop Firewire connector. For laptop use, you will need to
make sure you can get power to the camera. We recommend a Apricorn AFW6-4 adapter
available at the time of this writing from www.newegg.com. We also recommend getting a
FireCard400-e from Unibrain which has an external power adapter connector that can receive
external power for powering the cameras (see http://www.unibrain.com/ for more details).
4.2 GigE Wavefront Sensors
The AOS software supports any of the GigE cameras available from Allied Vision Technologies
(www.alliedvisiontec.com). We have found that these sensors work with many standard gigabit
Ethernet cards, but not all of them. AVT has an application note entitled, “Hardware Selection
for AVT GigE Cameras” (available currently at
http://www.alliedvisiontec.com/fileadmin/content/PDF/Support/Application_Notes/Hardware_S
election_for_AVT_GigE_Cameras.pdf) that lists the different tested hardware for GigE camera
acquisition including adapters and switches.
4.2.1 Power
Power to these cameras is provided either via a secondary port (often 12-pin Hirose) or over the
GigE link directly via the Power-Over-Ethernet (PoE) standard. The power application is
camera specific, so customers are encouraged to consult the camera manual for proper power
application.
4.3 SU320KTSW-1.7RT IR Wavefront Sensor
Do not mount the camera by the front end. This will cause damage to the sensor. Use the screw
holes under the camera body.
4.3.1 Mechanical Drawing
Below is a drawing of the approximate dimensions of the SU320KTS WFS in millimeters.

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NOTE: Dimensions are in millimeters.

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5 Software
The software is now documented in the AOS Adaptive Optics Software Manual.
6 Appendix: Select Camera Parameters Summary
Parameter
Fire-i
Webcam
Stingray
F-033B
Guppy
F-036B
Guppy
F-503B
Marlin
F-131B
SU320KTS
W-1.7RT
Prosilica
GT1920
X Pixel Size (μm)
5.6
9.9
6.0
2.2
6.7
25
4.54
Y Pixel Size (μm)
5.6
9.9
6.0
2.2
6.7
25
4.54
Maximum
Resolution (pixels)
640 x
480
656 x
492
752 x 480
2592 x
1944
1280 x
1024
320 x 256
1936 x
1456
Imager
Dimensions (mm)
3.6 x2.7
6.5x4.9
4.5x2.9
5.7x4.3
8.6x6.9
8.0x6.4
8.7x6.6
If your camera is not listed here, more information about the camera parameters can be found at
the camera manufacturer’s website.
Manufacturer
Website
Allied Vision Technologies
www.alliedvisiontec.com
Sensors Unlimited
http://www.sensorsinc.com/
Basler
http://www.baslerweb.com/

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7 Appendix: Legacy Sensor Information
7.1 USB Webcam Hartmann Sensors (discontinued)
The USB Webcam Hartmann Wavefront Sensor has been discontinued and is being replaced
with the Firewire Webcam Hartmann Wavefront Sensor. Here are notes for legacy users:
The webcam housing is plastic, and, as such, is
susceptible to fracture due to excessive force. When
mounting the webcam, use care so as not to drop the
device or tighten any mounting screws too
aggressively so as to avoid damaging the device.
Figure 7.1.2 shows how a 8-32 screw should be
used to connect the webcam Hartmann sensor to a
standard ½” laboratory post. AOS is not responsible
for any fracture damage induced by aggressive or
careless behavior.
To facilitate alignment, the wavefront sensor needs
to be mounted on a kinematic stage that allows the
sensor to be tilted in the two axes perpendicular to
the beam propagation direction. There are several different ways of creating a mount like
this. Figure 7.1.1 shows an AOS Hartmann Sensor attached to a ThorLabs KM100P
Kinematic Prism Mount in such a way as to enable both of these axes to be manipulated.
Unfortunately, the mount shown here does not allow the sensor angle to be manipulated
independent of motion the sensor relative to the optical axis, but for fine tuning the sensor
position it is effective.
7.1.1 General Installation Notes:
Install the software provided by the webcam manufacturer using the camera
manufacturer’s instructions.
Plug in the camera if you have not already done so
for the camera manufacturer’s software. Set it up to
be properly illuminated.
Try running the QuickCapture program provided by
the manufacturer and see if the camera is responding
to light.
Install the AOS Webcam Hartmann sensor.
7.1.2 Warnings:
Bright Illumination: The underlying webcam is
designed with firmware that protects it from bright
illumination. If the sensor is illuminated with a bright light during operation, the sensor
can enter into a mode where it no longer responds. In this situation, the webcam must be
unplugged and then plugged back into the computer to reset the device. In rare
situations, the computer must be restarted.
Figure 7.1.2 - Mounting of the
USB Webcam Hartmann sensor
to a standard 1/2" post.
Figure 7.1.1 - Mounting the AOS
Hartmann Sensor to a ThorLabs
KM100P kinematic prisim mount