What is the Crosstalk and Interchannel Straylight of the ULTRIS X20?
Crosstalk describes the contribution of light of one wavelength to light with a different wavelength being measured in a specific channel. For example, how much light of the wavelength 500 nm is measured in the channel at 700 nm? Typically, there are two possible ways crosstalk can occur:
A) Spectrally Dispersive Element Quality
Spectrally dispersive elements, like prisms, gratings, and filters, have different separation qualities based on their physical properties. For spectral thin-film filters, these qualities can simply be graded by the range of their optical densities (OD). A good filter in an imaging spectrometer will have a quality of OD2, thus blocking 1/100 of light with an unwanted wavelength.
The ULTRIS X20 features a blocking capacity of OD4 for all wavelengths over the complete range of the camera. This leads to an unprecedentedly low crosstalk of 1/10000, or less than 0.01% of unwanted light interfering with spectrum measurements.
B) Interchannel Straylight or Scattering between Channels
All cameras generate some sort of straylight in the optical system. This straylight is generated due to dust, optical defects, reflections on optical surfaces, or suboptimal coatings. Furthermore, the sensor itself scatters parts of the light back, and this light can be reflected from mechanical parts and optical elements back onto the sensor itself.
Some spectrometer designs are more prone to interchannel straylight, where light from one channel is scattered to neighboring channels, than others. This problem is especially typical of filter-on-chip setups since the filters have no physical boundaries between each other.
To reduce this issue, the ULTRIS X20 is equipped not only with sufficient antireflection coatings but also a mechanical surface coating, which offers very high straylight reduction from the visible to the near-infrared. Furthermore, each channel is mechanically and optically sealed against its neighboring channels. The camera features a very low interchannel straylight on a 50% white target of below 1%.
Conclusion
In conclusion, the ULTRIS X20 offers unprecedentedly low crosstalk, especially when compared to other video spectroscopy setups, like filter-on-chip designs. The amount of unwanted light in neighboring channels is two orders of magnitude lower than what is typically found in hyperspectral cameras, which results in magnificent spectral quality with an unprecedentedly small amount of interchannel straylight and crosstalk.
About the Author
Dr. René Heine is the Co-Founder and CEO of Cubert GmbH, a leader in real-time spectral imaging. Since founding the company in 2012, René has been instrumental in shaping Cubert’s technological direction and growth. He holds a Doctor of Physics degree from the University of Ulm, where he graduated magna cum laude, and completed his diploma thesis at Harvard Medical School. René’s deep expertise in physics and his vision for cutting-edge imaging technologies drive Cubert’s innovations and advancements in hyperspectral solutions.