THORLABS SBC-VIS User manual

SBC-VIS and SBC-IR
Soleil-Babinet
Compensator
User Guide

Soleil-Babinet Compensator
Table of Contents
Chapter 1 Introduction ........................................................................................................................1
Chapter 2 Setup ...................................................................................................................................2
2.1. Unpacking..................................................................................................................... 2
2.2. Basic Compensator Operation .................................................................................... 2
2.2.1. Digital Micrometer ................................................................................................................. 2
2.2.2. Graduated Rotation Dial ........................................................................................................ 2
2.2.3. 45° Detent Stops ................................................................................................................... 2
2.2.4. Kinematic Azimuth/Elevation (Tip/Tilt) Adjustment ............................................................... 2
2.3. Using Compensator with Crossed Polarizers............................................................. 3
2.4. Calibration..................................................................................................................... 4
2.4.1. Calibration Procedure ........................................................................................................... 4
Chapter 3 Setting the Compensator to a Specific Retardance ......................................................6
3.1. Setting the Compensator at the Calibration Wavelength........................................... 6
3.2. Setting the Compensator for other Wavelengths....................................................... 6
Chapter 4 Measuring an Unknown Retardance/Birefringence.......................................................7
Chapter 5 Optional LabVIEW Software and Serial Support............................................................8
5.1. Serial Interface Setup................................................................................................... 8
5.2. Software Installation..................................................................................................... 8
5.2.1. Stand-Alone Version ............................................................................................................. 8
5.2.2. LabVIEW Drivers ................................................................................................................... 9
5.3. Software Operation....................................................................................................... 9
5.3.1. Overview ............................................................................................................................... 9
5.3.2. User Interface Fields ........................................................................................................... 10
5.3.3. Stand-Alone Version ........................................................................................................... 11
5.3.4. Calibrating the Compensator .............................................................................................. 12
5.3.5. Setting the Compensator to a Target Retardance .............................................................. 13
5.3.6. Quitting the Stand-Alone Version ........................................................................................ 13
5.3.7. Running the Compensator Software with LabVIEW ........................................................... 13
Chapter 6 Theory of Operation ........................................................................................................14
Chapter 7 Cleaning and Maintenance .............................................................................................16
7.1. Cleaning the Optics.................................................................................................... 16
7.2. Cleaning the Compensator Housing......................................................................... 16
7.3. Micrometer Battery Replacement.............................................................................. 16
Chapter 8 Specifications...................................................................................................................17
Chapter 9 Mechanical Drawing ........................................................................................................18
Chapter 10 Regulatory ........................................................................................................................19
10.1. Waste Treatment is Your Own Responsibility .................................................. 19
10.2. Ecological Background ...................................................................................... 19
Chapter 11 Thorlabs Worldwide Contacts........................................................................................20

Soleil-Babinet Compensator Chapter 1: Introduction
Rev E, Sept. 14, 2018 Page 1
Chapter 1 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 Chapter 6 for more details).
Thorlabs offers two models: the SBC-VIS and SBC-IR which use quartz optics to cover a spectral range of 365-800
nm and 745-1650 nm respectively.
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:
 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

Soleil-Babinet Compensator Chapter 2: Setup
Rev E, Sept. 14, 2018 Page 2
Chapter 2 Setup
2.1. Unpacking
The compensator is shipped from Thorlabs 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 Thorlabs 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
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.
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.
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.
2.2.4. Kinematic Azimuth/Elevation (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.

Soleil-Babinet Compensator Chapter 2: Setup
Page 3 6570-D02
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 1 shows a typical arrangement.
Figure 1 Typical Arrangement of Compensator with Crossed Polarizers
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.

Soleil-Babinet Compensator Chapter 2: Setup
Rev E, Sept. 14, 2018 Page 4
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
Figure 2 Setup for Calibration Procedure
1. Set up the crossed polarizer configuration as shown in Figure 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.
WARNING
Never look directly into the laser! Project the laser onto a target screen 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 to 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.

Soleil-Babinet Compensator Chapter 2: Setup
Page 5 6570-D02
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.

Soleil-Babinet Compensator Chapter 3: Setting the Compensator to a Specific Retardance
Rev E, Sept. 14, 2018 Page 6
Chapter 3 Setting the 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)
XSBC = N * Xcal (Eq. 3.1)
An example of this equation is provided here:
Test wavelength = 632.8nm
Xcal = 14.55
N = 0.25 (i.e. quarter wave of retardance)
XSBC=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 an 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(λ1) ) * Xcal (Eq 3-2)
Where: XSBC is the micrometer setting to obtain the desired retardance, Xcal is the calibration from 2.4.1, N2 is the
desired retardance at wavelength λ2, λ2 is the new wavelength, and B(λ) is the birefringence of the SBC model. For
models SBC-VIS and SBC-IR, use equation 6-1 in Chapter 6 for B(λ).

Soleil-Babinet Compensator Chapter 4: Measuring an Unknown Retardance/Birefringence
Page 7 6570-D02
Chapter 4 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 crossed polarizer and DUT mount as shown in figure 1.
2. Verify the input and output polarizers.
3. Insert the compensator and rotate it until the spot is extinguished.
4. Insert the DUT into the rotation mount and insert it into the crossed 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 the DUT is perpendicular to the optical path.
6. Rotate the DUT to 45°.
7. Rotate the compensator to 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 using the following equation:
NDUT= 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, and 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, XDUT is the thickness of the DUT in µm, λ is the wavelength, and
NDUT is measured in µm.

Soleil-Babinet Compensator Chapter 5: Optional LabVIEW Software and Serial Support
Rev E, Sept. 14, 2018 Page 8
Chapter 5 Optional LabVIEW Software and Serial Support
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 give instantaneous readouts of the
compensator retardance at a user-specified wavelength.
Included are an RS-232 serial interface module, SPC interface cable for the compensator, and a CD with the
LabVIEWTM 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 Compensator.
The software was developed in National Instrument’s LabVIEW Version 6.0. 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).
The Software and Serial Port Kit Includes:
 CD with Micrometer Software, LabVIEW drivers, and Documentation
 Serial Interface Unit with DB9 Connection
 SDP Data Cable (Attaches Micrometer to Serial Interface Unit)
5.1. 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.
5.2. Software Installation
Please refer to the README.TXT file on the CD for specific installation instructions.
5.2.1. 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 runtime engine (included on the CD) be installed on the target PC in order
to operate.