The heliCam\u2122 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 \u2013 such as magnetic fields or millimeter waves. <\/p>\n\n
Three new publications demonstrate this potential from two very different perspectives. One paper utilizes a rubidium vapor cell and the heliCam\u2122 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\u2122. <\/p>\n\n
In the paper “Magnetic field camera for zero-field conditions,” Ronja Rasser and her colleagues present a camera-based optically pumped magnetometer for operation near the magnetic zero field.<\/p>\n\n
The actual sensor element is a rubidium vapor cell only 300 \u00b5m 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\u2122 C4 captures these small, modulated intensity changes across the surface in parallel and demodulates them directly in each pixel. <\/p>\n\n
With a binning of 5 \u00d7 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 \u00b5m. 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. <\/p>\n\n
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. <\/p>\n\n
To the publication in Optics Express<\/a><\/p>\n\n 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.<\/p>\n\n 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 \u2013 a so-called Glow Discharge Detector \u2013 as a converter. <\/p>\n\n 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\u2122 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. <\/p>\n\n 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 \u00d7 11 positions. From the measured values, the researchers reconstructed the image of an F-shaped metal object measuring approximately 50 \u00d7 60 mm. <\/p>\n\n 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. <\/p>\n\n To the publication in Electronics<\/a><\/p>\n\n 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\u2122 C4, but asks a further question: Do you actually need to arrange many individual glow discharge lamps for a flat detector array \u2013 or could the plasma within a single lamp already provide spatially separated measurement areas?<\/p>\n\n 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. <\/p>\n\n 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. <\/p>\n\nMaking Millimeter Waves Visible: Plasma as an Optical Converter<\/h3>\n\n
A Glow Discharge as a Natural Pixel Array?<\/h3>\n\n