heliCam™ Features in Research – From Magnetic Fields to Millimeter Waves
The heliCam™ from Heliotis does more than just make weak optical signals visible. Combined with suitable physical measurement principles, it can also provide information on quantities that a camera does not directly capture – such as magnetic fields or millimeter waves.
Three new publications demonstrate this potential from two very different perspectives. One paper utilizes a rubidium vapor cell and the heliCam as a high-resolution magnetic field camera. Two other papers investigate how millimeter waves can be converted into modulated near-infrared light using a plasma and subsequently detected with the heliCam.
Magnetic Field Camera: More Than 7,000 Measurement Points in a Single Vapor Cell
In the paper “Magnetic field camera for zero-field conditions,” the author and her colleagues present a camera-based optically pumped magnetometer for operation near the magnetic zero field.
The actual sensor element is a rubidium vapor cell only 300 µm thick. A laser beam shines through the entire cell. The local magnetic field influences the state of the rubidium atoms and thus the intensity of the transmitted light. The heliCam C4 captures these small, modulated intensity changes across the surface in parallel and demodulates them directly in each pixel.
With a binning of 5 × 5 camera pixels, the system achieves more than 7,000 usable measurement points within a circular area of approximately 4 mm in diameter. The resulting spatial resolution is about 40 µm. In the current setup, it was not limited by the atomic measurement principle, but primarily by interference at the uncoated windows of the vapor cell, which necessitated the binning of the camera pixels.
The researchers recorded, among other things, the spatial distribution of a magnetic field gradient oscillating at 130 Hz. The work thus shows that a single vapor cell can not only implement many measurement channels but also capture time-varying magnetic field patterns through imaging.
Making Millimeter Waves Visible: Plasma as an Optical Converter
The paper “First Demonstration of Lock-in Camera-Enabled Optical Up-Conversion Imaging for Millimeter-Wave Detection Using Glow Discharge Plasma” follows a completely different measurement principle.
Millimeter waves can penetrate optically opaque materials and are non-ionizing. However, sensitive two-dimensional detectors are often expensive, slow, or technically complex. The authors therefore use a small glow discharge lamp — a so-called Glow Discharge Detector — as a converter.
When modulated millimeter-wave radiation hits the plasma in the lamp, it slightly changes its emission in the near-infrared. This weak modulation is superimposed on a much stronger, continuous plasma glow. This is exactly where Lock-in detection comes into play: the heliCam C4 receives the same reference signal used to modulate the millimeter-wave source. Each camera pixel thereby specifically extracts the synchronous component of the optical emission and suppresses the uncorrelated background light.
In the experiment, the millimeter-wave source operated in the range of 100 to 105 GHz. A single Glow Discharge Detector was moved mechanically across a grid of 11 × 11 positions. From the measured values, the researchers reconstructed the image of an F-shaped metal object measuring approximately 50 × 60 mm.
The optical acquisition time was around 100 ms per scan position, compared to about 90 seconds for a previous camera-based method using image subtraction. This represents an improvement of nearly three orders of magnitude. However, the full recording took longer in the demonstrator because the single detector had to be moved mechanically between the grid points. The next logical step would therefore be a two-dimensional array of Glow Discharge Detectors that functions without mechanical scanning.
A Glow Discharge as a Natural Pixel Array?
The third paper, “Debye-length-resolved detection in glow discharge plasma: toward a self-contained focal plane array for millimeter-wave imaging,” builds on the same combination of millimeter waves, plasma up-conversion, and heliCam C4. However, this paper asks a further question: Do you actually need to arrange many individual glow discharge lamps for a flat detector array — or could the plasma within a single lamp already provide spatially separated measurement areas?
The starting point is the so-called Debye length. It describes the characteristic spatial scale over which electric charges are shielded in a plasma. The authors propose considering local plasma regions of this magnitude as distinguishable sensor elements. A phase-sensitive camera could read out the spatially distributed near-infrared emission of these regions, modulated by millimeter waves, in parallel.
Initial measurements show spatial differences in plasma emission that are consistent with locally varying responses to millimeter-wave excitation. However, the work is intentionally presented as a concept and outlook: Detection with proven resolution on the scale of the Debye length was not yet realized in the present experiment. Rather, the paper describes a possible path toward a compact, cost-effective millimeter-wave detector in which a single plasma discharge itself takes over the function of a focal-plane array.
A Common Trend: The Camera Becomes Part of the Sensor
The three papers deal with two very different physical quantities. However, they share a fundamental principle: The signal of interest is first translated into a small, spatially distributed change in light. The heliCam then does not simply capture an image, but demodulates the temporal signature in parallel at each pixel.
In the magnetic field camera, the rubidium vapor cell takes on the role of the sensor. In the millimeter-wave measurement, it is the plasma of a glow discharge lamp. Regarding both cases, pixel-wise Lock-in detection makes it possible to separate weak modulated signals from a much stronger optical background.
Particularly exciting is the development within the two plasma papers. The first publication demonstrates the complete measurement chain up to the reconstructed millimeter-wave image. The second already asks how the plasma itself could be further developed into a spatially resolved detector.
Such research shows how new measurement instruments can emerge from the combination of innovative sensor media and imaging Lock-in technology. We look forward to accompanying the next steps of these research groups with the heliCam.
You can find these and other papers related to heliotis cameras.
About Heliotis
Heliotis develops, manufactures, and distributes optical 3D measurement technology for industrial quality control. Their core competence is in the development of CMOS image sensors, FPGA-based cameras, and optical measurement technology. Thanks to sustainable investments in research and development, these 3D sensors are among the most accurate and fastest non-contact sensors in the world.
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