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Dispersion Measurement System
Chromatis™ Dispersion Measurement System
Software Screen Showing a Detected Interferogram and Calculated Dispersion
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Example data taken with the Chromatis™ dispersion measurement system to aid in optimizing an optical coating. The targeted GDD (black dashed line) for this 1030 nm mirror is -1200 fs2 over the 1020 to 1050 nm wavelength range (blue shaded area). The first two runs show significant error in the GDD.
2013 Category of Test, Measurement, and Metrology
Thorlabs' Chromatis™ Dispersion Measurement System characterizes the group delay dispersion (GDD) properties of reflective and transmissive optical components that are used with femtosecond pulsed lasers. Ultrafast pulses broaden as they propagate through an optical system; short pulse widths can be recovered by knowing the GDD induced by each optic and compensating for the distortions appropriately. For highly accurate and reliable results, the Chromatis™ uses time-domain white light interferometry (WLI) to measure the GDD. This dispersion measurement system includes software that guides the user through beam alignment (fringe optimization), automatically finds the zero time delay position (maximum fringe contrast), and rapidly measures the dispersion.
The Chromatis dispersion measurement system features a fiber-coupled stabilized halogen light source with an effective wavelength range from 500 to 2100 nm. This broadband source allows for characterization of ultrafast optics designed for use with Ti:Sapphire, Ytterbium fiber, and Erbium fiber lasers. Since the interferogram is recorded in the time domain, measurements are carried out with a single photodiode detector, rather than a spectrometer, and a built-in HeNe reference laser provides calibration for the wavelength axis. A Si photodiode for wavelengths from 500 - 1100 nm is included with the system; however, an InGaAs detector can easily be switched in for measurements in the 1000 - 1650 nm wavelength range. For more information about the InGaAs detector add on, please contact Applications@thorlabs.com.
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The user-friendly software includes the measurement procedures enabled by the system. The Zero-Degree, Transmision, and Angle Measurement modes are standard, while the Mirror Pair Measurement is available as an add on; contact Applications@thorlabs.com for details.
Typically, low dispersion optics require only hundreds of femtoseconds to capture an entire interference pattern, so it is often helpful to restrict the wavelength range of the incident light with optical filters to reduce the required scan range and overall noise. The Chromatis™ dispersion measurement system features six slots for optical filters, and bandpass filters covering the 500 - 700 nm, 600 - 1000 nm, and 950 - 1100 nm wavelength ranges are included for use with the Si photodiode. Since filtering reduces the overall intensity of the scan and, therefore, the interference contrast, the photodiode has variable gain settings to compensate for this attenuation.
To eliminate the need for additional tools, all mounts for user-provided optics include a tightening thumbscrew. Please note that optics mounted without thumbscrews should not be removed or replaced. Precision fixtures are locked into place or removed via a locking wheel; when not in use, the fixtures should be mounted on the baseplate in the dedicated storage area.
Step-by-step procedures with detailed on-screen instructions are provided for measurements on either reference or test optics. For example, to simplify the visual alignment of the interferometer, the user is shown which knobs should be adjusted, as well as animations that show fringes resulting from misalignment, near-alignment, and alignment. In the case of an advanced user, the step-by-step instructions can be switched off.
Please note that the Chromatis™ is factory calibrated to remove any residual dispersion from fixed system optics; the software is also precalibrated for the Si and InGaAs detectors.
Thorlabs has recently acquired the Chromatis™ Dispersion Measurement System from KMLabs and is currently finalizing the compliance requirements for international sale of this item. The information presented in this web presentation, the attached datasheet, and manual reflect current specifications for this item. Additional details, including potential updates to the specifications, will be provided once an internal evaluation of the product is completed. In the interim, please contact Applications@thorlabs.com to learn more about the Chromatis™ measurement system.
Thorlabs has recently acquired the Chromatis™ Group Delay Dispersion (GDD) Measurement System from KMLabs and is currently finalizing the compliance requirements for international sale of this item. The information presented in this web presentation, the attached datasheet, and manual reflect current specifications for this item. Additional details, including potential updates to the specifications, will be provided once an internal evaluation of the product is completed. In the interim, please contact Applications@thorlabs.com to learn more about the Chromatis™ measurement system.