IDS multi-camera imaging reveals the 3D structure of highly dynamic plasma jets
Researchers at the Leibniz Institute for Plasma Science and Technology (INP) use synchronized IDS industrial cameras to reconstruct plasma jet discharges in 3D, providing an experimental basis for analysing their spatial structure and behaviour.
en.ids-imaging.com
Plasma jets, in which ionised gas is emitted from a source in the form of a focused, highly dynamic, light-emitting structure, play a central role in numerous technological and medical applications, ranging from materials processing to plasma medicine. At the same time, plasma discharges are among the phenomena that are most difficult to study experimentally: They are small-scale, highly dynamic, erratic and change within a few microseconds.
At the Leibniz Institute for Plasma Science and Technology (INP) in Greifswald (Germany), the research group Medical Plasma Source Systems (MPS) is dedicated to addressing this challenge. Under the leadership of Dr Torsten Gerling, the team is investigating the fundamental properties of plasma sources used in medicine, using, among other things, image-processing-based measurement methods. A current research focus is the experimental investigation of the plasma discharge of the so-called kINPen plasma jet, an atmospheric-pressure cold plasma source developed at the INP that generates a highly dynamic, self-luminous plasma filament. To capture the highly dynamic discharge structure spatially, the researchers have relied from the outset on a synchronous multi-camera setup using industrial cameras from IDS.
The kINPen plasma jet under investigation is an atmospheric-pressure cold plasma source developed entirely at the INP; the plasma it generates leaves the device as an effluent and exhibits a highly dynamic discharge structure (1 µs period) with a very small spatial extent (0.1 mm diameter, 10 mm length). This combination of rapid temporal changes and small scale makes the kINPen a suitable reference system for experimentally investigating the spatial structure and propagation of individual plasma jet discharges.
Head of the kINPen plasma source with time-resolved discharge structure (16 µs exposure time).
It is precisely this spatial dimension that is the focus of the current works: “For us, the focus is on the three-dimensional structure of the plasma discharge,” explains Artur Wittig, a research fellow at the INP. “The experimental observation of this structure is an important step towards better understanding and controlling plasma jets and their mechanisms of action.”
Image processing at the limits of physics
The demands placed on image processing are exceptional. A plasma discharge is a highly dynamic phenomenon that changes over time scales of just a few microseconds and extends over a distance of only about ten millimetres. Extremely short exposure times are required to make individual discharge channels visible. In this application, exposure times ranging from 9.35 to 30.03 microseconds are used. Images are captured in monochrome as 8-bit single frames. “The key point here is that all the cameras must operate in perfect synchronisation, as this is the only way to capture the same features within a very short timeframe,” emphasises Artur Wittig. Although two-dimensional single-frame images provide high-resolution views of the discharge, they allow only limited conclusions to be drawn about its spatial structure. Particularly in the case of self-luminous, highly dynamic objects such as plasma filaments, the actual three-dimensional distribution remains speculative without additional views. It is only by capturing images simultaneously from multiple angles that it becomes possible to reliably reconstruct spatial features such as curvature, coiling or lateral deflection of the discharge.
“We need to ensure that the same plasma filaments are actually captured in every image,” explains Dr Torsten Gerling, head of the research group. “This requires very precise timing and a high degree of repeatability in relation to the plasma source.”
Calibration of the multi-camera setup on the kINPen using a 3D-printed reference object.
Stable imaging despite highly dynamic discharge
Although a single measurement without a surface may produce multiple filaments – known as guided streamers, which are short-lived, thread-like discharge channels in the plasma – measurements involving a surface usually show a clearly dominant discharge path. This behaviour is attributed to what is known as the derivative mode: A guided streamer forms a conductive channel to the surface. A kind of transient glow discharge then flashes erratically along this channel. Due to the memory effect, metastable particles from previous discharges facilitate the re-ignition of further guided streamers. These largely follow the same path, slightly offset by the flow of gas.
Particularly in the case of high-frequency excitation of the kINPen, this effect results in the visible plasma structure forming in a spatially reproducible manner across multiple discharges. This makes it possible to visualise it reliably.
This physical property provides a key basis for the systematic investigation of highly dynamic plasma discharges using image-processing-based measurement techniques.
3D reconstruction of the discharge structure as a point cloud with a centre line (red) to illustrate the discharge channel; normals for orientation (blue).
Multi-view stereo for 3D reconstruction
To experimentally characterise the spatial structure of the plasma discharge, the INP employs a multi-view stereo approach using five IDS cameras operating in synchronisation. The plasma discharge is captured from different angles at the same time. In addition to precise calibration of the camera system, a key requirement for a robust spatial reconstruction is the reproduction of the fine discharge structures with as little distortion as possible.
High‑aperture 75 mm lenses from IDS are used, featuring a large 1.2‑inch image circle and an f/2.8 aperture. This optical performance is required because the discharge has an axial length of less than 10 mm and a width of less than 1 mm.
“At an observation distance of around 500 mm, the plasma filament is hardly self‑luminous; its brightness is almost comparable to that of a firefly,” explains Dr‑Ing. Philipp Mattern, supervisor and examiner of the master’s thesis conducted at INP. “It is only the combination of the sensor and the optics that enables high-quality images to be captured despite exposure times of just a few microseconds.”
During image analysis, distinctive structures within the plasma discharge are identified and used as cross-image point correspondences, from which the three-dimensional structure of the discharge is reconstructed as a point cloud.
Structure of the self-luminous filament at a distance of 3 mm (exposure time: 40.76 µs).
“The point clouds obtained in this way provide, for the first time, a reliable basis for investigating the discharge paths,” explains Artur Wittig. “This allows us not only to visualise the plasma structure, but also to analyse it systematically.”
Camera selection with a focus on triggering and synchronisation
The image processing task is handled by five industrial cameras of the uEye CP U3‑31J0CP Rev. 2.2 type from IDS, which are well suited for parallel operation in multi‑camera setups thanks to their triggering and synchronisation capabilities.
The conceptual foundation for this setup, as well as the decision to use IDS hardware, was the brainchild of Dr Philipp Mattern. Some aspects of the scientific and technical support were provided through his engineering firm, M.E.S.S. (Mattern Engineering & Software Solutions). “Based on my experience with similar applications, it was clear that this camera system would be able to meet the high optical and temporal requirements,” explains Mattern.
Multi-camera setup with five IDS industrial cameras positioned at 90° angles around the discharge point
The main factors influencing the choice were the capabilities for precise hardware triggering, exact synchronisation and the ability to reliably control very short exposure times. Due to the highly dynamic nature of the plasma discharge, precise triggering, exact synchronisation and reproducible exposure times in the microsecond range are crucial for capturing the same features in every image. The global shutter sensor used enables distortion-free imaging of the short-lived plasma structure and ensures stable image quality even at exposure times in the microsecond range.
The camera is equipped with a square Sony Pregius S CMOS sensor (IMX546) and offers a resolution of 8.13 megapixels. The combination of a global shutter and backside illumination (BSI) enables short exposure times even in low-light conditions – a key requirement for the reliable imaging of self-luminous, short-lived plasma structures.
“The comprehensive documentation provided by IDS was also helpful, as was the technical support in designing and validating the configuration of multiple cameras for simultaneous image capture and the stable setup of the multi-camera system,” says Artur Wittig.
Integration is carried out via the IDS peak SDK, which enables the configuration and simultaneous operation of multiple cameras. The ability to reliably save and reuse camera settings ensures that experimental measurement series can be carried out under consistent conditions and compared with one another. The control and automation of the multi‑camera setup are carried out via the IDS peak API for Python, which conveniently enables parallel operation, triggering and image storage.
More than just visualisation: an experimental proof of concept
The multi-camera methodology developed is not merely intended for illustrative purposes. Rather, it represents an experimental proof of concept: For the first time, it has been demonstrated that the highly dynamic plasma discharge of a kINPen jet can be reconstructed as a three-dimensional point cloud and subsequently analysed structurally. This provides a practical basis for further investigations into the spatial propagation of plasma jet discharges.
Structural analysis of the plasma discharge in a kINP jet
Furthermore, the method is not limited to kINPen, but can also be applied to other small discharge structures with relatively little effort.
Outlook
The current work continues to focus on the analysis of plasma jet discharges, including under altered operating parameters such as gas flow or discharge mode. Furthermore, other applications are conceivable, particularly in situations where dynamic structures need to be studied with high temporal and spatial resolution. Imaging techniques such as Schlieren or BOS (Background Oriented Schlieren) methods are also the subject of ongoing research. These are optical imaging techniques that do not capture the objects themselves, but rather changes in the fluid, such as air or the working gas. In future, they will open up new possibilities for visualising invisible flows and density differences in the vicinity of the plasma discharge, thereby complementing the experimental analysis.
IDS’s perspective and technical assessment
The project impressively demonstrates how IDS’s flexible and high-performance image processing solutions are opening up new avenues in experimental research – and thus enabling us to see what was previously invisible. “In applications involving highly dynamic objects such as plasma discharges, it is not individual features that are decisive, but rather the combination of a global shutter sensor and precise, reproducible exposure control via hardware triggering to synchronise multiple cameras,” explains Heiko Seitz, Product Marketing Manager at IDS. “These features make it possible to capture consistent image data even in multi-camera setups, thereby providing a reliable foundation for demanding image processing tasks in research and development.”
Image rights: Leibniz Institut für Plasmaforschung und Technologie e.V. (INP)
© 2026 IDS Imaging Development Systems GmbH
Camera
Model used: U3-31J0CP Rev.2.2
Camera family: uEye CP
Lens used: IDS-20M12-C7528
Customer
The Leibniz Institute for Plasma Science and Technology (INP) has been conducting applied basic research and development in the field of low-temperature plasmas for over 25 years.
(https://www.inp-greifswald.de/en/research/more/kompetenzzentrum-diabetes-karlsburg/medical-plasma-source-systems)
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