THORLABS Chromatis Manuel utilisateur

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

𝑃ℎ𝑎𝑠𝑒 = 𝜑

𝐺𝑟𝑜𝑢𝑝 𝐷𝑒𝑙𝑎𝑦 (𝐺𝐷) = 𝑑𝜑

𝑑𝜔

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 applications@thorlabs.com.

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

•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

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 applications@thorlabs.com.

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

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