THORLABS Chromatis User manual

Chromatis™
Dispersion Measurement System
User Guide

Chromatis™ Dispersion Measurement System
Table of Contents
Chapter 1 Safety.........................................................................................................................1
Chapter 2 Description.................................................................................................................3
Chapter 3 Instrument Overview..................................................................................................5
Chapter 4 Measurement.............................................................................................................8
4.1.1 Zero-Degree Reflection and Transmission Fixture (Ø1” and Ø1/2” Optics) ........................................................ 9
4.1.2 Angle of Incidence Reflection Fixture................................................................................................................ 10
4.3.1 Configuration Settings Tab................................................................................................................................ 18
4.3.2 Motor Control Tab............................................................................................................................................. 20
4.3.3 S-Polarization Tab.............................................................................................................................................. 20
4.3.4 P-Polarization Tab ............................................................................................................................................. 21
Chapter 5 Reference Optics and Calibration ..............................................................................22
Chapter 6 Wavelength Selection Filters and Detector Gain Settings...........................................23
Chapter 7 Changing Detectors...................................................................................................25
Chapter 8 Specifications ...........................................................................................................27
Chapter 9 Mechanical Drawings................................................................................................ 28
Chapter 10 Certifications and Compliance...................................................................................30
Chapter 11 Warranty and RMA Information................................................................................31
Chapter 12 Thorlabs Worldwide Contacts ...................................................................................32

Chromatis™ Dispersion Measurement System Chapter 1: Safety
Rev. A, September 27, 2022 Page 1
Chapter 1 Safety
Warning
All statements regarding safety of operation and technical data in the manual will only apply
when the unit is operated correctly as it was designed for.
Laser Radiation Warning
The user may be exposed to laser signals after they have been attenuated via internal
components to < 1 mW in the range of 500 - 650 nm, which is Class II laser radiation. Use of
controls or adjustments or performance of procedures other than those specified herein may
result in hazardous radiation exposure.
Do not look into the optical output when the device is operating. Always disable the light
sources with the instrument head on-off switch before changing detectors, optics, or
measurement fixtures. It is possible that a Class 1 laser product with a highly diverging beam
can produce high enough irradiance levels near to or in contact with the source (for instance,
a fiber tip) so that skin or iris injury is possible.
Shock Warning
Before poweringthe unit on, make sure that the line voltage range marked on the power supply
agrees with your local supply, and that the protective conductor of the 3-conductor power cord
is correctly connected to the protective earth contact of the socket outlet. Improper grounding
can cause electric shock resulting in severe injury or even death. Do not operate without cover
installed.
Remove the AC power cord before changing the light bulb in the power supply. Do not open
the power supply when the device is connected to power. The power supply contains AC power
and will put the user at risk of shock.
Explosion Warning
This instrument must not be operated in an explosion endangered environment.

Chromatis™Dispersion Measurement System Chapter 1: Safety
Page 2 TTN202268-D02
Warranty
Do not open the CHROMATIS Dispersion Measurement System housing. There are no user-
serviceable parts in this product. Opening the device will void your warranty. Any modification
or servicing of this system by unqualified personnel renders Thorlabs free of any liability. This
device can only be returned when packaged into the complete original packaging, including all
foam packing inserts. If necessary, ask for replacement packaging.
Note: This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant
to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful
interference when the equipment is operated in a commercial environment. This equipment generates, uses, and
can radiate radio frequency energy and, if not installed and used in accordance with the instruction manual, may
cause harmful interference to radio communications. Operation of this equipment in a residential area is likely to
cause harmful interference in which case the user will be required to correct the interference at his own expense.
This device must only be operated with proper shielded connection cables. This product has been tested and
found to comply with the limits according to IEC 61326-1 for using connection cables shorter than 3 meters
(9.8 feet).
Laser Safety Precautions
It is recommended that all persons who use or are near devices emitting laser light be aware of the potential
hazards.
•Never look into the end of an optical cable connected to an optical output device that is operating. Direct
exposure to laser radiation can severely injure the human eye.
•Eye and skin exposure to direct or scattered laser radiation is hazardous and is considered potentially
extremely harmful.
•Install the laser in an enclosed area with access restricted to trained personnel. Clearly label the area and
mark the entrance with the class of laser (Class II).
•Never leave the optical outputs of the device on and unattended.
•Ensure that this device is not assembled, operated, or repaired by inexperienced or untrained personnel.
•Ensure that all mirrors and optics used are securely positioned and fixed to prevent movement. Prevent
stray reflections from surfaces at all times.
•Do not allow reflective objects to be placed in the laser beam outputs of this device. Laser light scattered
from a reflective surface can be as damaging as the original beam. Objects such as rings, watchbands, and
metal pens or pencils can be hazardous.
•Install the device so that the laser beam outputs are not at eye level.

Chromatis™ Dispersion Measurement System Chapter 2: Description
Rev. A, September 27, 2022 Page 3
Chapter 2 Description
The Chromatis is a white light interferometer (WLI) designed to measure the dispersion characteristics of reflective
and transmissive optics. The WLI itself can be implemented as a simple interferometer as shown in Figure 1.
Figure 1 White Light Interferometer: A broadband, temporally incoherent light source (such as a
halogen bulb) is collimated and sent through an interferometer consisting of a broadband, low
dispersion beamsplitter, and two delay arms. One arm (reference arm) uses a low dispersion mirror,
while the other arm (test arm) contains the test mirror. The time delay (Δt) between the two arms is
scanned across Δt = 0. In the regions around Δt = 0, the white light signals from each arm interfere
with each other, giving an interference pattern that is detected by a photodiode and recorded by a
computer. To provide a distance reference for the time delay scan, a coherent source (HeNe laser) is
co-propagated with a vertical offset to the white light. The HeNe fringes are recorded on a separate
photodiode.
The white light interference pattern contains information about the relative phases of the light from the test arm
and the reference arm. A computer is used to process the interference pattern and extract the phase and
dispersion properties of the mirror under test. This device also can measure the dispersion of a transmissive
sample by replacing the test mirror with a low dispersion mirror and placing the transmissive sample in the beam
path.
The Chromatis dispersion measurement system directly measures the phase of the optic under test and converts
the phase to dispersion through numerical derivatives
a
:
𝑃ℎ𝑎𝑠𝑒 = 𝜑
𝐺𝑟𝑜𝑢𝑝 𝐷𝑒𝑙𝑎𝑦 (𝐺𝐷) = 𝑑𝜑
𝑑𝜔
a
More in-depth information can be found in: S. Diddams and J. Diels, "Dispersion measurements with white-light
interferometry," J. Opt. Soc. Am. B 13, 1120-1129 (1996).

Chromatis™Dispersion Measurement System Chapter 2: Description
Page 4 TTN202268-D02
𝐺𝑟𝑜𝑢𝑝 𝐷𝑒𝑙𝑎𝑦 𝐷𝑖𝑠𝑝𝑒𝑟𝑠𝑖𝑜𝑛 (𝐺𝐷𝐷) = 𝑑2𝜑
𝑑𝜔2
𝑇ℎ𝑖𝑟𝑑 𝑂𝑟𝑑𝑒𝑟 𝐷𝑖𝑠𝑝𝑒𝑟𝑠𝑖𝑜𝑛 (𝑇𝑂𝐷) = 𝑑3𝜑
𝑑𝜔3
𝐹𝑜𝑢𝑟𝑡ℎ 𝑂𝑟𝑑𝑒𝑟 𝐷𝑖𝑠𝑝𝑒𝑟𝑠𝑖𝑜𝑛 (𝐹𝑂𝐷) = 𝑑4𝜑
𝑑𝜔4
This method of dispersion measurement is very versatile because only a single element detector is needed for the
white light measurement and automatic wavelength calibration is built-in because of the HeNe optical reference.
This means that a dispersion measurement can be made at any wavelength that you can provide a broad
bandwidth source and a detector. In addition, an increase in real resolution is obtained by scanning over a longer
delay.
There are some practical limitations to this measurement. The Chromatis dispersion measurement system uses a
fiber-coupled white light source, which simplifies the optical setup but introduces some wavelength limitations.
Typical fiber optic cables attenuate more in the visible and greatly in the UV. In addition, the white light source
was chosen to provide the broadest measurement bandwidth possible and to provide a smooth spectral curve.
The white light source in the Chromatis allows easy characterization of mirrors designed for Ti:sapphire (around
800 nm), Yb:fiber (around 1030 nm), and Er:fiber (around 1550 nm) lasers, along with some harmonics. The output
spectrum from the white light source tapers off greatly in the visible and has no light output below 360 nm. The
typical configuration of the Chromatis system includes a silicon detector, which can measure from 500 nm to 1100
nm. For NIR applications, a InGaAs detector operating over the 900 nm to 1650 nm wavelength is also available
separately.
In addition, real world measurement issues like light noise, amplifier noise, and digitization put a limit on the
amount of time delay you can scan before the integrated noise becomes greater than the signal. Chromatis uses
low noise components, but the time delay scan still is limited to less than approximately 10,000 fs for typical
measurements. At this level, absolute noise is high, but very sharp and very high dispersion features can be
resolved; however, most optics do not require this extreme resolution. Optics that do require this resolution have
very large dispersions and the relative noise is still very low (GDD noise/GDD value). At more moderate resolutions
(5 nm is ideal for most optics), both the absolute and relative noise is low and standard deviations of less than 5
fs2are typical over most of the measurement range for only a few scans. The Chromatis software interface has
built-in averaging so that the effects of this noise can be reduced simply by increasing the number of scans.

Chromatis™ Dispersion Measurement System Chapter 3: Instrument Overview
Rev. A, September 27, 2022 Page 5
Chapter 3 Instrument Overview
Optical Head and Fixtures
The Chromatis instrument is designed to be easy to use. There are two separate user-swappable fixtures available
that enable three different measurement types for Ø1/2” and Ø1” optics, which are discussed in the next chapter.
For fixtures that enable measurements on a mirror-pair or Ø2” optics, please contact [e-mail].
Figure 2, Figure 3, and Figure 4 show an overview of the Chromatis optical head.
Figure 2 The Chromatis Optical Head: The fixture being used for the current measurement is
installed in the measurement area. The fixture not in use can be locked to the baseplate in the
fixture storage area. The detectors are contained in a user-accessible section; the included silicon
detectors can be replaced with the CHRDETN InGaAs detectors for NIR applications. The light
selection switch and emission indicator are shown on the front of the device. The umbilical and
data port is on the side.
Umbilical
and Data
Port
Light
Selection
Switch
Fixture
Installed for
Measurement
Fixture Storage
Area
Detectors
Alignment Knob
Alignment Viewing Screen

Chromatis™Dispersion Measurement System Chapter 3: Instrument Overview
Page 6 TTN202268-D02
Figure 3 The custom optic holders have thumbscrews for easy optic mounting while standard
mirror mounts use a typical setscrew mounting. The thumbscrews on the custom optic holders
contain spring-loaded nylon tips to provide the right amount of mounting force on the optics.
Figure 4 Umbilical and Data Port: This panel contains the instrument ON/STANDBY switch. The on
position is denoted by “I” and the standby position is denoted by “O”. The silver cable is the fiber
optic cable carrying the light from the various light sources to the instrument head. The D-sub
connector provides power and control for the various components of the Chromatis system. The
USB Motor and Data connections are plugged directly into the included laptop computer.
Power Supply Unit
The electronics for Chromatis dispersion measurement system are contained within a rack-mountable 2U
enclosure, which also can operate free-standing. There only is one user-serviceable component within the power
supply enclosure: the white light source bulb. Instructions on how to replace the white light bulb are included
with each device. There is a power switch in the back of the power supply enclosure (Figure 5) that should remain
on unless the instrument is being moved or the bulb is being replaced. When the Chromatis system is not in use,
or when optics, measurement fixtures, or the photodiodes are being removed, turn the instrument off using the
on-standby switch on the optical head (shown in Figure 4), but leave the power supply on-off switch in the On
position. This will disable all the laser light sources for increased safety and longevity. Leaving the power supply
on ensures that the motor position does not have to be re-established each time the instrument is used.
Polaris
Mount
Setscrew
Thumbscrew
On/Standby
Switch
USB 2.0 Type-B
Connector
USB 2.0 Type-B
Connector
15-Pin Male
D-Sub Connector
Fiber Optic Cable
for Light Sources
(Not Removable)

Chromatis™ Dispersion Measurement System Chapter 3: Instrument Overview
Rev. A, September 27, 2022 Page 7
Figure 5 Chromatis power supply front (upper picture) and back (lower picture) panels. The power
supply on-off switch is next to the power cord plug. The umbilical cables plug into the Fiber Out
and Power Out ports.
Shipping List
The Chromatis dispersion measurement system contains the following components:
•Chromatis Optical Head (Armored Fiber Cable is Permanently Attached)
•Dust Cover for Optical Head
•Chromatis Power Supply Unit
•0° Reflection and Transmission Precision Fixture
•Angle of Incidence Reflection Precision Fixture
b
•Calibrated System Optic for Transmission Measurements
•Calibrated Reference Optics (Qty. 2)
•AD1 Ø1" OD Adapter for Ø1/2" Optic, 0.25" Thick
•Laptop with Pre-Installed Software
•USB 2.0 Type-A to Type-B Cable, 10' (3.05 m) Length (Qty. 2)
•15-Pin D-Sub Cable, Female to Male, 10' (3.05 m) Length
•Region-Specific AC Power Cord
•Torx T10 Key for White Light Bulb Replacement
b
The sliding portion of the angle of incidence reflection fixture, which includes a POLARIS-K1 mirror mount with the mounted
calibrated system optic, is packaged separately from the fixture.
15-Pin Female D-Sub
Connector
AC Power
Input
Light Source
Output Port
(SMA Connector)
On/Off
Power Switch

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 8 TTN202268-D02
Chapter 4 Measurement
Alignment and Fixture Overview
The Chromatis dispersion measurement system is designed to enable easy and fast measurements of mirrors and
transmissive optics in three different modes of operation: zero-degree reflection, transmission, and angled
reflection. The included fixtures are mechanically registered and easily swappable. There are two separate fixtures
that provide these different measurements, as described below. For a fixture that facilitates measurements on a
complimentary mirror pair, please reach out to [e-mail].
Figure 6 The Chromatis optical head showing the fixture measurement position. Fixtures are
interchangeable and allow different measurement modes.
Figure 7 Fixture locking and unlocking occurs through rotation of the locking wheel in the fixture
baseplate. Rotate the wheel to the left to lock a fixture into place and rotate the wheel to the right
to unlock a fixture for removal from the baseplate.
Please note that no tools are necessary to change fixtures. Do not remove the fixture baseplate or loosen any of
the screws affixing the baseplate to the instrument breadboard.
Fixture
Location

Chromatis™ Dispersion Measurement System Chapter 4: Measurement
Rev. A, September 27, 2022 Page 9
Warning:
When changing out fixtures, ensure that the instrument On/Off switch is in the OFF position to
disable laser light from the aperture.
4.1.1 Zero-Degree Reflection and Transmission Fixture (Ø1” and Ø1/2” Optics)
Figure 8 Fixture designed for measurement of either a reflective optic at 0° angle of incidence (top
picture), or a transmissive optic at 0° - 70° angle of incidence (bottom picture).
Transmission
Optic Under Test
Goes Here
System
Optic
Optic Under
Test

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 10 TTN202268-D02
4.1.2 Angle of Incidence Reflection Fixture
Figure 9 Fixture for the measurement of a reflective optic at a user-defined angle of incidence. The
optic is placed in a front-surface-registered mount (black) and the angle of incidence is read off of the
scale on the rotation stage. The system optic is then positioned to reflect the measurement light back
into the device for analysis.
Mirror Under Test
System Optic
Angle scale

Chromatis™ Dispersion Measurement System Chapter 4: Measurement
Rev. A, September 27, 2022 Page 11
Optical Alignment with Software Guidance
The Chromatis software is designed to guide the user through each type of measurement in a step-by-step way.
The main software home screen has options for the four types of measurements. Please note that the fixture
required for the mirror pair measurement is not included with the Chromatis dispersion measurement system. To
purchase the complimentary mirror-pair fixture, contact [e-mail].
Figure 10 Home Screen of the Chromatis software. The four measurement types are available for
selection. To purchase the complimentary mirror-pair fixture required for the mirror pair
measurement, contact [e-mail].
Clicking on any of the measurement types will open a screen where you can select between a reference optic
measurement (used to verify the correct operation of the Chromatis system) and a test optic measurement (to
measure the optic under test).
Figure 11 Each measurement has two possible procedures: Reference Optic or Test Optic. Reference
Optic Alignment is used to verify that the instrument is operating properly with a known “reference”
optic. Test Optic Measurement is used to measure any other optics.

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 12 TTN202268-D02
Within the test or reference instructions is a step-by-step procedure with on-screen instructions. The user can
navigate through these instructions by clicking the “Next” and “Back” buttons. Completed steps will have a
checkmark by them.
Figure 12 Measurement instructions with “Next” and “Back” buttons in the bottom right. Follow the on-
screen instructions to perform a measurement. At any time in the procedure, you can click “Home” in
the top right and go back to the Home screen. At this time, skipping steps is not enabled.
The general steps for a typical optic measurement are:
1. Always turn the instrument switch to the Standby position prior to removing optics or fixtures from the
measurement area. This will minimize the exposure to the Class II laser sources exiting the aperture into
the measurement area.
2. Place the correct fixture and optic in the Chromatis optical head, then turn the instrument switch back to
On to re-enable the light sources.
3. Align the optic under test.
4. The software automatically finds the zero-delay position around which measurements take place.
5. If necessary, the user can make final adjustments to the alignment at the zero-delay position.
6. After alignment is finished, the system is ready to take data and measure the dispersion of the optic under
test.
Of these steps, the alignment step is the most difficult to master, so we have devoted several instruction screens
to help the user obtain the proper alignment.

Chromatis™ Dispersion Measurement System Chapter 4: Measurement
Rev. A, September 27, 2022 Page 13
Figure 13 Alignment Instructions: An animation on the right-hand side shows what the fringes
should look like when close to optimum alignment while the picture on the left shows which
alignment knobs to adjust. If visual alignment is too difficult for a user, “Oscilloscope Alignment”
may be selected. This changes the screen to a view of the detector signals.
The first few alignment instruction screens assist users in performing the visual alignment step. Step 4 shows the
alignment knobs that need to be adjusted and an animated example of what the optical fringes should look like
on the view screen. There are three cases, which include overlapped but no fringes, some fringes, and the perfect
fringe pattern (shown in Figure 13). Step 4 also contains a separate alignment method, accessible by clicking
“Oscilloscope Alignment”.
Figure 14 Oscilloscope Alignment Screen: The user can use the oscilloscope signal to optimize the
alignment of the optic under test if the visual alignment is difficult.

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 14 TTN202268-D02
Figure 15 Find Zero Results Popup Screen: This screen allows the user to determine if the zero-delay
position has been found correctly. At zero delay, the white light will interfere, causing detectable
oscillations.
If zero was found correctly, advancing will take the user into the Scan step. The software takes a reference scan
at the last saved scan parameters to allow the user to verify that interference signals are being detected. The
results are shown upon entering the Scan screen.
Figure 16 Results of the initial scan showing interference patterns are detected properly (bottom right).
The user now can choose the scan settings that are appropriate for the optic under test.
If the initial scan looks good, the user should set the scan settings to values appropriate for the optic under test.
The wavelength range should be set for the region of interest, and the time range should be set so that the whole
interference pattern is captured. The resolution of the wavelength points is inversely proportional to the time
range and also depends on the center wavelength as shown in the table below. Low dispersion optics like
protected silver or most simple quarter-wave-stack mirrors generally only require 150 to 500 fs to capture the

Chromatis™ Dispersion Measurement System Chapter 4: Measurement
Rev. A, September 27, 2022 Page 15
whole interference pattern. In general, the smaller the time range, the smaller the noise. High dispersion optics
generally require 500 to 2000 fs to capture the whole interference pattern. There is not one time range setting
that is optimal for every optic. A good procedure is to start with a small time range, then increase the time range
until the dispersion features do not change any more and the relative noise is still low. A series of different
interference patterns showing correct and incorrect time range settings are shown in Figure 17, Figure 18, and
Figure 19.
Time Range
Δλ at 600 nm
Δλ at 800 nm
Δλ at 1064 nm
Δλ at 1550 nm
150 fs
8.01 nm
14.23 nm
25.18 nm
53.43 nm
250 fs
4.80 nm
8.54 nm
15.10 nm
32.06 nm
500 fs
2.40 nm
4.27 nm
7.55 nm
16.03 nm
1000 fs
1.20 nm
2.13 nm
3.78 nm
8.01 nm
2000 fs
0.60 nm
1.07 nm
1.89 nm
4.01 nm
4000 fs
0.30 nm
0.53 nm
0.94 nm
2.00 nm
Table 1 Wavelength Resolution for Various Time Range Settings
Figure 17 High Dispersion Optic Interference Pattern: The left interference pattern uses a time range
of 250 fs and does not capture the entire interference pattern. A time range of 1000 - 2000 fs is
appropriate for this high dispersion optic (2000 fs shown in right graph).
Figure 18 Quarter-Wave Stack Reflector at 800 nm Center Wavelength: Too long of a time scan (left
graph) will cause excess noise in the measurement. A time range of 250 - 500 fs is appropriate for this
optic (500 fs Time Range shown to the right).

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 16 TTN202268-D02
Figure 19 Two more interference patterns with appropriate time delays. The left graph shows the
interference pattern for a 3 mm thick piece of fused silica for a Time Range of 800 fs. The right graph
shows a chirped mirror designed for the visible at a 500 fs Time Range.
Once the appropriate time range and wavelength range has been set, the user should start a scan (by clicking Start
Scan) with the desired number of averages. 5 - 10 averages is a good place to start, and more averaging can be
added as necessary. As the system takes data, the GDD graph is updated in real time with the average result (white
line) and the standard deviation of the measurements (blue fill) as shown in Figure 20. After the scan is complete,
the user can select which data to display by selecting from the drop-down menus for each graph (Figure 21). All
the graphs are editable, so you can change the scale to your liking.
Figure 20 The results of a completed scan are shown. The data is shown in white, with the standard
deviation of the data shown with blue fill (plus and minus one standard deviation).
Figure 21 Different graphs can be selected for display by choosing from the drop-down menus above
each graph.
Once the data is satisfactory, clicking “Save Data” will open a dialog box where the user can save all the data from
the run in a .CSV file. The file contains column headers so it can be imported easily into many data analysis

Chromatis™ Dispersion Measurement System Chapter 4: Measurement
Rev. A, September 27, 2022 Page 17
programs. Saved along with the .CSV file is a .TXT file containing any user-specified notes as well as the scan
settings for that data set. Clicking “Create Report” opens a screen where the user can select six graphs for display
at one time (Figure 22). This custom report can be saved as a JPEG or printed.
Figure 22 Report generation feature where six graphs can be displayed at once. These graphs can be
printed or saved as a .JPEG file.
These reports also can be generated from previously saved data by clicking the “Load Previously Saved Data”
button on the Home screen (Figure 10). This concludes the instructed measurement walk-through.

Chromatis™Dispersion Measurement System Chapter 4: Measurement
Page 18 TTN202268-D02
Optical Alignment Without Software Guidance
The Chromatis software provides step-by-step instructions for how to align each measurement fixture for the
current optic under test. However, you can choose to use the advanced panel to make measurements without
step-by-step instructions (Figure 23).
Figure 23 Advanced Settings Button on Home Screen. Clicking this button will take you to the Advanced
Panel where settings can be modified, and measurements can be made without going through step-
by-step instructions.
The advanced panel has four different tabs that allow you to modify the settings of the instrument and view data
without going through the step-by-step instructions.
4.3.1 Configuration Settings Tab
Figure 24 Configuration Settings Screen: Advanced users can use this screen to manually set some of the
Chromatis hardware and software parameters.
Advanced
Settings