First Demonstration of Lock-In Camera-Enabled Optical Up-Conversion Imaging for Millimeter-Wave Detection Using Glow Discharge Plasma

This study presents a novel approach in millimeter wave (MMW) imaging by demonstrating the first experimental implementation of an imaging system that integrates optical up-conversion within a glow discharge detector (GDD) plasma alongside a phase-sensitive lock-in camera. In this novel approach, incident MMW radiation, modulated with an ON–OFF signal, strikes the GDD, which functions as an up-conversion sensor, transforming the MMW signal into ON–OFF-modulated near-infrared (NIR) optical emissions. This upconverted light is then captured by the lock-in camera, which synchronously demodulates the optical signal at each pixel. By simultaneously receiving the upconverted optical emissions and the original reference signal used to modulate the MMW radiation, the camera achieves synchronous demodulation of the incoming light at each pixel. This advanced configuration enables the direct extraction of amplitude and phase information with pixel-level synchronous demodulation, while actively and effectively increasing the SNR and eliminates the uncorrelated background plasma emissions. The proposed optical up-conversion system effectively addresses existing limitations, offering a unique combination of advantages. By inheriting the fundamental benefits of GDD, such as cost-efficiency per unit, simplified electronic design, and robust resistance to high radiation levels, the system demonstrates enhanced noise suppression and increased sensitivity. Validation experiments utilizing LED modulation verify an optical acquisition time of approximately 100 ms per scan position (pixel dwell time), representing a significant improvement of several orders of magnitude over conventional optical acquisition approaches. In the present proof-of-concept implementation, complete image formation additionally includes the mechanical scanning time required for image reconstruction. Ultimately, this work establishes an improved paradigm for MMW imaging, advancing the development of compact, rapid, and cost-effective imaging systems for advanced non-ionizing imaging applications.