Chromatis is the first and only production-grade test instrument designed specifically to address measurements of group delay dispersion in optical components. It is a broadband optical test instrument that quickly and accurately characterizes the full dispersive properties of optical components and coatings. Carefully managing optical dispersion is critical for optimal performance of ultrafast laser systems, multi-layer mirrors, and multiple quantum well structures. Chromatis is user friendly, self-calibrating, and highly accurate.
Read the Photonics Spectra article on Chromatis:
This year at the SPIE Laser Damage Symposium, KMLabs’ Chromatis instrument was part of the judging for the Thin Film Coating Competition. The 2015 Coating Competition: "Broadband low-dispersion mirror thin film damage competition". Broadband low dispersion mirrors are a fluence-limiting component in short pulse lasers. For this study the mirrors must meet a minimum reflection of 99.5% GDD of <+/- 100 fs2 over a spectral range of 773 nm +/- 50 nm. The participants selected the coating materials, design, and deposition method. Laser damage testing was performed using a raster scan method with a 150 ps pulse length on a single testing facility to facilitate a direct comparison among the participants. Group Dispersion Delay measurements were also performed on each sample. Details of the deposition processes, cleaning method, coating materials, layer count, and spectral results are shared. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [LLNL-ABS-668929].
- Group Delay Dispersion (GDD) resolution: ± 5 fs2
- Measures both polarizations simultaneously
- high speed measurements - typically a few seconds per optic
- He-Ne reference laser for automated, built-in self-calibration of every measurement. Chromatis does not use a spectrometer, and no spectrometer calibration is necessary
- Standard designs for 1” and 2" diameter optics, highly repeatable fixtures and opto-mechanical referencing
Four measurement modes, including both Transmission and Reflection, with precision fixtures:
- 0° Angle of Incidence (AOI) in Reflection
- 5° - 70° AOI in Reflection
- 0° -70° AOI in Transmission
- Mirror pair measurement with variable AOI (6° -54°) (available as upgrade option)
- Reference optics for reflection and transmission modes of operation
Two user-replaceable detector modules (Silicon module included with standard system):
- Silicon: 500nm – 1100nm
- InGaAs: 1000nm – 1650nm (available as upgrade option)
- Simple, intuitive graphical user interface for technicians or power users. Generate and customize your measurement reports.
- Laptop computer included, with pre-installed measurement and control software
- Includes installation and training DVD and online web-based training. On-site installation and training visit available as upgrade option.
Typically, for optical coatings, the primary metrics are Transmission and Reflection, and often their polarization dependence. But a femtosecond pulse consists of a broadband set of wavelengths, with very specific phase relationships – as discussed in the last slide. GDD is the largest contributor to these effects (as well as TOD and FOD), and as mentioned can be controlled by careful manipulation of the coating layers. This is no easy feat, and coating companies expend great effort to control their layer thicknesses. As with so many measurements, though, phase can be a more sensitive measure of what’s really going on, and the example here demonstrates that.
The example below shows where a coating company wanted to make a coating with a fixed amount of GDD over a wavelength range around 1030nm. Even with specialized deposition monitoring methods, it took three iterations to get this coating correct. Such coatings are generally quite challenging.