THORLABS SBC-VIS User manual

Operations Manual
Soleil Babinet Compensator
Models: SBC-VIS, SBC-UV, SBC-IR
Ver 1.4
15.001mm
Fast Axis
Model SBC-VIS
THORLABS
Thorlabs, Inc
435 Route 206N
Newton, NJ 07860
[phone] Ph, [phone] Fax
www.thorlabs.com

Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Table of Contents
1.0 Introduction .......................................................................................................................................................... 3
Table 1-1 Standard Features..................................................................................................................................... 3
Table 1-2 Specifications ............................................................................................................................................ 4
Figure 1-0 – Mechanical Specs ................................................................................................................................. 4
2.0 Setup ................................................................................................................................................................... 5
2.1 Unpacking............................................................................................................................................................ 5
2.2 Basic Compensator Operation ............................................................................................................................ 5
2.2.1 Digital Micrometer............................................................................................................................................. 5
2.2.2 Graduated Rotation Dial ................................................................................................................................... 5
2.2.3 45° Detent Stops .............................................................................................................................................. 6
2.2.4 Kinematic Az/El (Tip/Tilt) Adjustment ............................................................................................................... 6
2.3 Using compensator with Crossed Polarizers....................................................................................................... 6
Figure 2-1 Crossed Polarizer Setup .......................................................................................................................... 6
2.4 Calibration............................................................................................................................................................ 7
2.4.1 Calibration Procedure....................................................................................................................................... 7
3.0 Setting Compensator to a specific retardance .................................................................................................... 9
3.1 Setting the Compensator at the Calibration Wavelength .................................................................................... 9
3.2 Setting the Compensator for Other Wavelengths................................................................................................ 9
4.0 Measuring an Unknown Retardance/Birefringence........................................................................................... 10
Appendix A – Optional LabView Software and Serial Port...................................................................................... 11
A.1 Serial Interface Setup........................................................................................................................................ 11
A.2 Software Installation.......................................................................................................................................... 12
A.3 Software Operation ........................................................................................................................................... 12
Appendix B – Theory of Operation .......................................................................................................................... 18
B.1 Quartz Sellmeier and Birefringence .................................................................................................................. 19
B.2 MgF2Sellmeier and Birefringence Data............................................................................................................ 19
Appendix C – Cleaning and Maintenance ............................................................................................................... 20
Cleaning the Optics ................................................................................................................................................. 20
Cleaning the Compensator Housing........................................................................................................................ 20
Micrometer Battery Replacement ............................................................................................................................ 20
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
1.0 Introduction
The Soleil-Babinet Compensator is a continuously variable, zero order retarder (waveplate) which operates over a
broad wavelength range. The classical design of the compensator consists of a long birefringent wedge mounted
on an adjustable slide. A fixed wedge mounted to a compensator plate completes the optical system. The
retardance is adjusted by moving the position of the long wedge relative to the short wedge using a precision
digital micrometer. This allows the retardance to vary continuously while maintaining a uniform retardance across
the aperture at any given setting (see Appendix B Theory of Operation for more details).
Thorlabs offers three models: the SBC-VIS and SBC-IR use quartz optics to cover a spectral range of 400-
1000nm and 1000-2000nm respectively. The SBC-UV uses magnesium fluoride optics to extend the compensator
range into the UV from 140nm to 400nm.
Our standard Soleil-Babinet Compensators are uncoated for broad spectral operation. To minimize reflection
losses when using the compensator over narrow wavelength ranges, AR-coated versions are available upon
special request.
Applications include birefringence compensation, precision retardance measurements and high resolution
ellipsometry.
Standard features of all the compensator versions include:
Table 1-1 Standard Features
• Continuously Variable Retardance
• Uniform Retardance over Full Aperture
• 3 Wavelength Ranges (UV, VIS, IR)
• Digital Micrometer Readout
• Graduated Rotation Ring with Vernier Readout
• 45° Index Stops for Rapid Setup
• Adjustable Kinematic Tilt Adjustment
• Optional RS-232 Interface & Software available
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Table 1-2 Specifications
Wavelength Range: 140 to 400nm (SBC-UV)
400 to 1000nm (SBC-VIS)
1000 to 2000nm (SBC-IR)
Retardance Adjustment: 0 to 2π(full wave)
Clear Aperture: 10mm diameter
Beam Deviation: < 1 arc min
Transmitted Wavefront Error: < λ/4
Surface Quality: 40-20 Scratch-Dig
Digital Readout Resolution: 0.001mm
Rotation: 360° continuous
Rotation Division Scale: 1° increments
Detent Index Stops: Every 45°
15.001mm
OPTICAL CENTER
DIGITAL MICROMETER
OPTICS HOUSING
GRADUATED ROTATION DIAL
CLEARANCE HOLE FOR #8 (M4) SCREWS (3)
KINEMATIC ADJUSTABLE TILT MOUNT
9"
4"
3.8"
2.1"
2.7"
1.5"
2.8"
0.85
0.55 0.40
Figure 1-0 – Mechanical Specs
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
2.0 Setup
2.1 Unpacking
The compensator is shipped from the factory ready to run. Carefully unpack the compensator and inspect the
optics by looking through the aperture. Remove any loose particles of dust by gently blowing a stream of
compressed air across the optic. If there are any signs of damage on the optics, contact the factory for an
immediate replacement.
2.2 Basic Compensator Operation
The compensator can be thought of as a retardation plate, or waveplate, with an adjustable retardance. Just like a
conventional waveplate, the retarder has a fast and slow axis. The fast axis is indicated on the front cover of the
optics housing.
The retardance is varied by adjusting the digital micrometer which moves the long wedge inside the compensator.
The retardance is controlled by total optical path which is determined by the position of the long wedge relative to
the fixed wedge and the compensating optic.
The adjustment range of Thorlabs Soleil Babinet Compensators is a minimum of one full zero wave of retardance
over the operating spectral range. Just like quartz waveplates, the retardance of the compensator is wavelength
dependent. Fortunately, calibrating the compensator for any given wavelength is relatively simple and is typically
done in the field for maximum accuracy (see Section 2.4).
2.2.1 Digital Micrometer
Thorlabs compensators include a precision digital micrometer to allow fast and accurate adjustments. The digital
readout can be nulled which greatly simplifies calibrating the compensator. The micrometer can display the
compensator wedge position in either units of millimeters or inches. The choice of units is not critical since the
calibration is a relative position measurement.
The digital micrometer includes an interface which can be used with the optional RS-232 interface and LabView
driver software to automate the compensator operation (see Appendix A).
The micrometer is battery operated and turns on automatically whenever the adjustment knob is moved or one of
the control buttons on the micrometer is pressed. The micrometer will automatically shut itself off after a period of
inactivity to preserve battery life. If the display starts to get dim or the micrometer no longer operates, the battery
should be replaced (see Appendix C).
2.2.2 Graduated Rotation Dial
The graduated rotation dial has laser engraved markings every 1 degree. The matching index on the
compensator body has a Vernier scale to allow for very precise continuous rotational adjustments. A thumbscrew
on the side of the compensator body locks the rotating dial in place.
To adjust the rotation, loosen the thumbscrew on the side of the compensator housing, rotate the compensator
into position, and then re-tighten the thumbscrew.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
2.2.3 45° Detent Stops
For many compensator applications, the rotational fine adjustment is set once and the compensator is then
rotated in 45° increments (e.g. when calibrating the compensator or measuring an unknown retardance). The
Thorlabs compensators include spring loaded detent stops spaced every 45° for this purpose. Simply grab the
compensator housing and rotate the compensator to the desired detent position.
Note: if the detent adjustment becomes too tight or too loose, the spring tension may need to be adjusted (see
Appendix C).
2.2.4 Kinematic Az/El (Tip/Tilt) Adjustment
The compensator includes two fine pitch ¼-80 adjustment screws on the back of the compensator housing to
provide adjustment of the azimuth and elevation for precise alignment. This design is based on a proven high-
quality kinematic approach used throughout Thorlabs mirror mounts.
2.3 Using compensator with Crossed Polarizers
Many compensator applications require using compensator between a pair of crossed polarizers in a classic
generator/analyzer configuration. In such cases, the polarizers are spaced apart with their polarization axis
rotated 90° to each other so that no light is transmitted. The compensator is then placed between the two
polarizers such as when calibrating the compensator. When using the compensator to measure an unknown
retardance, the optic to be tested is also placed between the crossed polarizers along with the compensator.
For best accuracy, high quality calcite polarizers mounted in precision rotation mounts should be used. Also, the
device under test should also be mounted in a precision rotation stage so that the optic axis of the device can be
precisely aligned.
Thorlabs carries a complete line of high quality calcite polarizers, rotation mounts and other accessories useful for
constructing this setup. Figure 2-1 shows a typical arrangement.
L
R
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Generator DUT Soleil Babinet Analyzer
Compensator PRM1 Rotation Stage
SM1PM10 Polarizer Mount
TR-series Post
PH series Post Holder
Figure 2-1 Crossed Polarizer Setup
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Generator – This stage is the input for the test laser and uses a precision polarizer (e.g. GT10 Glan Taylor calcite
polarizer) mounted in a precision rotation stage to generate a very pure linear state of polarization.
Analyzer – A second polarizer stage (identical to the generator) is used for the output analyzer. Normally this
polarizer is rotated so that its transmission axis is 90° with respect to the analyzer to achieve the crossed
condition (minimum light transmission).
DUT – When measuring the retardance of an unknown device (i.e. waveplate), the device under test (DUT) is
placed in between the crossed polarizers with its optical axis rotated 45° from the generator polarization axis.
Soleil Babinet Compensator – The compensator is placed in between the crossed polarizer, and like the DUT,
its optic axis is rotated 45° from the generator polarization axis.
2.4 Calibration
Normally, the first step to using a compensator is to calibrate it at the operating wavelength. If this is not possible,
it may be necessary to calibrate at a test laser wavelength (i.e. a single mode HeNe) and extrapolate to the
operating wavelength. Note: the SBC-COMM Serial Interface and Software package automates most of this
process.
2.4.1 Calibration Procedure
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Generator
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Analyzer
Soleil Babinet
Compensator
Laser
Target Screen
Figure 2-2 Calibration Setup
1. Set up the crossed polarizer configuration as shown in Figure 2-2
2. With the compensator removed from the setup, rotate the analyzer so that the spot transmitted onto the target
screen is minimized. At this point the polarizers are crossed.
If the calibration laser is polarized, it may be necessary to first rotate the generator so that the laser is not
blocked by the generator.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Warning: Never look directly into the laser ! Use a target screen to project the laser onto for indirect
viewing.
3. Insert the compensator in between the two polarizers. Adjust the tip/tilt adjustments so that the compensator
is perpendicular to the optical beam. This is best done by observing the back reflection from the compensator
to the test laser and adjusting the compensator so that the reflected spot is close the laser output aperture.
4. At this point, there should be some light transmitted onto the projection screen. Loosen the rotation locking
thumb screw and rotate the compensator until the transmitted spot is extinguished. Tighten the thumb screw.
At this point the fast axis of the polarizer is aligned with one of the transmission axes of the two polarizers.
5. With the rotation dial locked in place, rotate the compensator to the next 45° detent stop. There should be
some light transmitted to the target screen unless the compensator happens to be at exactly one full wave of
retardance.
6. Adjust the micrometer until the spot is extinguished. This is the first of two null to be used as a full wave
reference.
7. Press the ZERO/ABS button on the micrometer to reset the display to 00.000.
8. Continue adjusting the micrometer so that the laser spot becomes visible again. Continue adjusting in this
direction until the spot extinguishes. This is the second null.
9. Record the micrometer reading at this position. The distance indicated on the micrometer corresponds to the
calibration distance equal to one full wave of retardance at the test laser wavelength.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
3.0 Setting Compensator to a specific retardance
3.1 Setting the Compensator at the Calibration Wavelength
The calibration distance can be used to set the compensator to any fractional wave of retardance at the
calibration wavelength using the following relationship:
Xcal = calibration distance (obtained from 2.4.1)
N = desired retardance (in waves)
X
SBC = N * Xcal (eq. 3-1)
Example:
Test wavelength = 632.8nm
Xcal = 14.55
N = 0.25 (i.e. quarter wave of retardance)
X
SBC = 14.55 * 0.25 = 3.638 = micrometer setting to get a quarter wave of retardance.
3.2 Setting the Compensator for Other Wavelengths
Sometimes it is not possible or convenient to calibrate the compensator at the operating wavelength. For
example; the compensator is to be used in a Nd:YAG system but for logistical reasons can only be calibrated
using a low power HeNe.
In such cases, the compensator target position can be extrapolated using the calibration obtained in 2.4.1
together with the basic retardance equations for the compensator. The following equation calculates the
compensator position at the target wavelength and retardance:
XSBC = N2* λ2* B(λ2) / (λ1 * B(λ2) ) * Xcal (eq 3-2)
where: XSBC is the micrometer setting to obtain the desired retardance
XCAL is the calibration from 2.4.1
N2is the desired retardance at wavelength λ2
λ2is the new wavelength
B(λ) is the birefringence of the SBC model
For models SBC-VIS and SBC-IR, use equation B-1 in Appendix B for B(λ). For SBC-UV, use equation B-2.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
4.0 Measuring an Unknown Retardance/Birefringence
One of the applications for the Soleil Babinet Compensator is to measure the retardance of an unknown device.
From this the birefringence can easily be calculated as well. To measure the retardance of an unknown sample:
1. Set up the cross polarizer and DUT mount as shown in Figure 2-1.
2. Verify the input and output polarizers (generator and analyzer) are crossed.
3. Insert the compensator and rotate it until the spot is extinguished.
4. Insert the DUT into the rotation mount and insert into the cross polarizer setup making sure the DUT is
perpendicular to the optical path.
5. Rotate the DUT until the laser spot is extinguished on the projection screen. At this point, the optical axis of
DUT is aligned with one of the polarizer transmission axes.
6. Rotate the DUT 45°.
7. Rotate the compensator 45°.
8. Adjust the compensator until the spot is extinguished again and record the micrometer reading at this point as
XSBC.
9. The retardance at the test wavelength can now be calculated:
N
DUT = 1.0 - XSBC / XCAL (eq. 4-1)
where: NDUT is the retardation of the device at the test wavelength
XSBC is the micrometer reading from step 8.
XCAL is the calibration from 2.4.1.
To calculate the birefringence from the measured retardance, the thickness of the part must be measured
precisely (i.e. using a micrometer or other device).
B(λ) = NDUT * λ/ XDUT (eq.4-2)
where: NDUT is the retardation measured above
X
DUT is the thickness of the DUT in µm
λis the wavelength NDUT was measured at in µm.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Appendix A – Optional LabView Software and Serial Port
Extend the versatility of your compensator by using our SBC-COMM serial interface and compensator software.
The software combines an easy to use graphical interface with the performance models for all of our
compensators to allow the user to easily and quickly calibrate the compensator and “dial in” the desired
retardance at any wavelength.
Also included is a real-time mode which monitors the compensator position and gives instantaneous readouts of
the compensator retardance at a user specified wavelength.
Included are a RS-232 serial interface module, SPC interface cable for the compensator, and a CD with the
LabView drivers and a stand-alone LabView Runtime library. The SBC-COMM LabView Drivers and Serial
Interface Kit is compatible with all versions of the Thorlabs Soleil Babinet Compensators.
The software was developed in National Instrument’s LabView™ Version 6.0. A LabView Runtime Library is
included on the CD so that the software can be run stand alone.
Also included are the compensator LabView drivers for experienced users who want to adapt the compensator to
their own specific needs (you’ll need to have a licensed copy of LabView on your system).
Software and Serial Port Kit:
• CD with Micrometer Software, LabView Drivers, and documentation
• Serial Interface Unit w/ DB9 connection
• SDP Data Cable (attaches micrometer to Serial Interface Unit)
A.1 Serial Interface Setup
The compensator computer interface must be connected to a standard 9-pin serial port on the PC. If necessary,
use a 25-to-9 pin adapter (available at most local PC supply stores).
1. Select the serial port that the compensator will be connected to and note the port number (e.g. COM1, COM2)
as this will be needed later when running the software.
2. Unpack the Serial Interface Unit and SDP cables.
3. Attach the mini-DIN side of the SPC cable to the mating connector on the bottom of the compensator
micrometer. This is a keyed connector and it may be necessary to rotate the connector to align the pins with
the mating sockets.
4. Attach the rectangular end of the SPC cable to the mating connector on the Serial Interface Unit. This is also
a keyed connector and can only be plugged in one way.
5. Attach the DB9 serial cable to the PC and note which port this is for later use.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
A.2 Software Installation
Stand Alone Version
The software consists of a stand alone version which does not require any programming skill to operate.
The stand alone version requires that the LabView run time engine (included on CD) be installed on the
target PC in order to operate
LabView Drivers
A LabView vi file is also included for users familiar with LabView programming and who would like modify
the compensator software. This requires a licensed version of LabView V6.i or higher (not included) in
order to run.
Please refer to the README.TXT file on the CD for specific installation instructions.
A.3 Software Operation
Overview:
The optional RS-232 interface and LabView drivers extend the versatility of the Soleil Babinet Compensator by
allowing automated measurements, easy wavelength conversion, and the ability to talk to the compensator from a
remote LabView program.
A serial interface on the micrometer, referred to as an SPC port by the micrometer manufacturer, allows the
position of the micrometer to be read remotely by a LabView program. Using this interface, we’ve developed a
LabView program that automates much of the manual calculations that are typically needed. For instance, with
two simple clicks of the mouse button, the compensator can be completely calibrated at the test wavelength.
We’ve embedded the wavelength-dependent birefringent data for all versions of the compensator into the
software to allow extrapolation of the retardance into any wavelength across the operating range. This allows the
compensator to be calibrated with a common lab laser (e.g. HeNe). The software is then used to calculate the
precise position the micrometer must be adjusted to in order to obtain the desired retardance at the target
wavelength.
Included on the CD are a stand-alone version (for users who do not own LabView ) as well as the LabView vi files
for those who wish to experiment and customize the program.
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Figure A.1 Compensator User Interface Screen
User Interface Fields
The fields on the user interface screen have two different background colors to distinguish the field type:
- White background fields are user input fields which require input from the user.
- Yellow background fields are calculated fields and cannot be modified by the user.
General Parameters
Model (user input) – Select the model compensator to be used with the software
Options: SBC-UV, SBC-VIS, SBC-IR
Serial Port (user input) – Select the serial port the compensator is attached to on the PC
Options: COM1, COM2, COM3, COM4
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Full Wave Calibration
Set Starting Null (button & display) – During calibration, the first null first found by manually adjusting the
retardance using the micrometer. Once the null is found, this button is pushed by the user and the software
records this position and displays it in the text box.
Set Ending Null (button & display) – During calibration, the micrometer is manually adjusted until the second null
is found (to traverse one full wave of retardance). Once the null is found, this button is pushed by the user and
the software records this position and displays it in the text box.
Enter Calibration Source Wavelength (user input) – The wavelength of the calibration laser is entered here.
This value is used to complete the full wave calibration.
Full Wave Distance (calculated field) – The software calculates the full wave distance in micrometer units as the
difference between the starting and ending nulls and displays the result here.
Target Data Input
Enter Target Retardance (waves) (user input) – Enter the desired retardance to set the compensator to.
Enter Target Wavelength (nm) (user input) – Enter the wavelength that the compensator is to be used at.
Target Micrometer Position (calculated field) – The software calculates the micrometer position that the
compensator must be set to by the user in order to get the Target Retardance at the Target Wavelength.
Current Position at Target Wavelength
Retardance (calculated fields) – As the micrometer is adjusted, the software reads the current position and
calculates the retardance at the target wavelength and displays it in three formats – waves, radians, and nm.
These fields are updated continuously once the Start button is pressed.
Waves (bar graph) (calculated field) – A bar graph displays the retardance in graphical format. The graph is
updated continuously once the Start button is pressed.
Micrometer (display only) – The current micrometer position is displayed continuously once the Start button is
pressed.
Press to Start / Stop (button) – Once the compensator has been calibrated, the software can begin polling the
micrometer and display the updated retardance fields continuously by pressing the Start button.
Note: the micrometer serial interface is powered by the lithium battery inside the micrometer. Leaving the
software in the continuous polling mode will eventually drain this battery. In order to preserve battery life, the
polling should be stopped when the unit is not in use.
Stand Alone Version
After installation, the software is ready to run as a stand alone program. During the installation process, the
LabView Runtime Engine, freely distributable program that is required to run the stand alone version, is installed.
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The installation will create a selection in the Start Menu – Programs called SBC. When this is selected, the
software will begin loading all the necessary modules and present the following screen.
Running the software:
Step 1. Select the correct COM port in the lower left of the screen. When ready press the START button.
Step 2. Select the correct compensator model.
After a brief appearance of a banner screen, the User Interface Screen as shown in Figure A2 will be
displayed. At this point the software is running and should respond to button presses.
If the software is not responding, check the COM port and if necessary, quit the program and re-start
it using the correct COM port.
Figure A2 – Stand Alone Version of User Interface Screen
Calibrating the Compensator:
In order the calibrate the compensator, you will need two linear polarizers mounted in rotation stages
and a calibration laser. Usually a HeNe laser is used as the calibration laser but other lasers could be
used as well as long as the spectral line width is not too large.
Although this procedure looks involved, after performing it once or twice you will become familiar with
it to the point that calibrations will be quick and easy.
Tip: Thorlabs carries a complete line of polarizers, optics mounts, rotation stages, and accessories.
You can find everything you need at www.thorlabs.com.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Step 1. Set the polarizers, compensator, and test laser as shown in Figure 2.2.
Step 2. With the compensator removed from the setup, rotate one of the two waveplates until the two
polarizers are exactly crossed at 90°.
Hint: It helps to place a target screen after the last polarizer so that the transmitted beam can be
safely observed. The polarizers are crossed when this beam vanishes.
Step 3. Re-insert the compensator back into the setup. The beam will re-appear since the compensator will
introduce an arbitrary elliptical polarization which is not extinguished completely by the second
polarizer.
Step 4. Loosen the rotation lock screw and rotate the compensator until the beam disappears again. At this
point, the fast axis is aligned with the transmission axis of one of the two polarizers. Tighten the lock
screw.
Step 5. Check the tip and tilt adjustment by observing the reflected beam and adjust the kinematic adjustment
screws on the back plate until the compensator is perpendicular to the beam propagation. If
necessary, repeat Step 4 to ensure the fast axis is still in alignment with the polarizer.
Step 6. The compensator must now be rotated so that the fast axis is 45° to the linear polarizer. The
compensator has spring loaded detent stops that allow the compensator to be easily positioned.
Firmly grasp the compensator optics housing and rotate the compensator 45°. If the compensator
does not move readily, the detent spring tension screw may need to be loosened first.
At this point, the compensator is aligned and ready for calibration.
Step 7. Adjust the micrometer clockwise and find the starting null point. This is the first micrometer position
closest to 0.0000 that the beam extinguishes. At this point the retardance is exactly zero waves.
Step 8. Press the Set Starting Null button to capture this location. The screen will update the text box above
the button with the current micrometer value.
Optional: If you prefer, you can press the ZERO button on the micrometer to set this position to 0.000
however this is not necessary since the software will do the necessary calculations if you leave it as
is.
Step 9. Adjust the micrometer counterclockwise to find the second null. At this point, the retardance is exactly
one wave.
Step 10. Press the Set Ending Null button to capture this location. At this point, the software calculates the
distance of one full wave of retardance.
Warning: Do not null the micrometer display from this point on. Doing so will invalidate the calibration
and you will need to repeat this procedure.
Step 11. If you haven’t done so already, enter the wavelength of the calibration laser in the “Enter Calibration
Source Wavelength” input box. This can be done either before or after the above steps.
At this point the compensator is accurately calibrated and ready to be used.
Setting The Compensator To A Target Retardance
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Once the compensator is calibrated, the software will allow you to easily set the compensator to any fractional
retardance within the operating spectral range of the unit.
Step 1. Enter the desired retardance in the “Enter Target Retardance” field. The units are in waves.
Step 2. Enter the wavelength that the target retardance is to be set for in the “Enter Target Wavelength” field.
This is necessary since the retardance is a function of wavelength for birefringent materials.
Step 3. The software will automatically calculate the position that the micrometer needs to be adjusted to
obtain the target retardance and display it in the “Target Micrometer Position” field. The user must
manually adjust the compensator to this position,
Step 4. At this point, you can turn on the automatic polling mode by pressing the “Press to Start” button. The
software will continuously poll the micrometer and update the values in the retardance display and
bar graph.
Tip: Be sure to press the “Stop” button when finished to preserve the micrometer battery life.
Quitting the Stand Alone Version
To exit the software, select the file option from the File pull down menu. This will completely shut down the
software modules.
If you click on the ‘x’ close window button, you will need to shut down all of the individual windows that are loaded
with the SBC software as well.
Running Compensator Software within LabView
Running the software within LabView is identical to the stand alone version. Make sure all of the following
modules are available for loading:
sbc.vi
b-quartz.vi
b-mgf2.vi
readmic.vi
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Appendix B – Theory of Operation
The classic Soleil Babinet Compensator design is based on two birefringent wedges with their optic axis aligned
lengthwise and a compensator plate with its optic axis rotated 90° from the wedges. The retardance through the
total optical path is:
N
SBC = B(λ) * (X2 – X1) / λ
As seen in Figure B-1, distance X1 is fixed. However, by sliding the long wedge along the direction shown in
Figure B-1, distance X2 can be varied continuously thereby the changing the retardance continuously as well.
Since the wedge angle for the fixed and moving wedge are the same, the optical path length X2 is uniform across
the aperture. This is a unique feature of Soleil Babinet Compensators.
Figure B-1 Compensator Optics
As can be seen in the basic compensator equation above, the retardance of the compensator is a function of the
birefringence which is wavelength dependent. The birefringence can be calculated from the Sellmeier equations
below.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
B.1 Quartz Sellmeier and Birefringence
ne λ ( ) 1.28851804 1.09509924
λ
2
.
λ
21.0210186410 2
.
1.15662475 λ
2
.
λ
2100
no λ ( ) 1.28604141 1.07044083
λ
2
.
λ
21.0058599710 2
.
1.10202242 λ
2
.
λ
2100
B λ () n
e
λ () n
o
λ ()
(eq B-1)
B.2 MgF2Sellmeier and Birefringence Data
nomgf2 λ () 1 .487551072
λ
2
.
λ
20.04338408
2
0.39875034 λ
2
.
λ
2.09461442
2
2.312035347 λ
2
.
λ
223.793604
2
nemgf2 λ () 1 .41344023
λ
2
.
λ
2.03684262
2
.50497499 λ
2
.
λ
2.09076162
2
2.4904862 λ
2
.
λ
223.77199519
2
Bm λ () n
emgf2
λ () n
omgf2
λ () (eq B-2)
Note: the wavelength, λis in µm.
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Soleil-Babinet Compensator Operations Manual – Doc # N0073-D01 Rev A Ver 1.4
Page 20
Appendix C – Cleaning and Maintenance
Under normal operating conditions, the compensator requires very little maintenance. Most problems can be
traced to either a dead battery or dirty optics. Follow the guidelines below if needed.
Cleaning the Optics
Most of the time, simply blowing dust or debris off the input aperture with a gentle breeze of compressed air is all
that is needed. If the input window needs further cleaning, use an optics wipe with propanol or acetone and lightly
wipe the optics surface.
Using excessive amounts of acetone may soften the optics mounting adhesive and cause the optics to become
loose.
Note: Taking the compensator housing apart may disturb the optical alignment and is not recommended. Contact
the factory if service is needed.
Cleaning the Compensator Housing
The housing can be wiped cleaned with a lint free rag wetted with propanol or a commercial window cleaner. Do
not soak the housing – it is not watertight and any moisture introduced inside the compensator may cause
condensation problems.
Micrometer Battery Replacement
The micrometer uses a 1.5V type SR44 miniature battery. If the micrometer display goes dim or does not come
up at all, it is time to replace the battery. The battery compartment is located on the back of the micrometer. Using
the tool provided with the micrometer, a large bladed screwdriver or a coin, unscrew the battery cover, remove the
old battery and replace with a fresh one. Discard the old battery properly.
If the micrometer display does not come up after replacing the battery, contact the factory for assistance.
Thorlabs, Inc
435 Route 206N
Newton, NJ 07860
[phone] Ph, [phone] Fax
www.thorlabs.com
The Soleil Babinet Compensator was developed and manufactured for Thorlabs by Nova Phase Inc, a custom
and OEM optics manufacturer. For more information on Nova Phase products and capabilities visit their website
at www.novaphase.com.