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Optical and Quantum Sensing and Precision Metrology II

Millimeter wave sensing and imaging using Autler-Townes induced fluorescence in Rydberg vapor

Daniel Mechael, G. S. Pati, Renu Tripathi

Published Mar 19, 2025• 0 citations
Publisher

Abstract

We present a millimeter-wave imaging system based on fluorescence induced by Autler-Townes splitting in a four-level atomic Rydberg system. By employing counter-propagating probe and coupling beams, we create a plane of atoms in a dark state that is sensitive to incident mmWaves at 91.4 GHz. Objects placed in the mmWave beam path diffract the beam which, when imaged onto the cell using a PTFE lens, induce AT splitting in regions of higher intensity, increasing 780 nm fluorescence at 780 nm. Imaging this fluorescence with an optical camera effectively images the incident mmWave field. The system demonstrates a temporal response time of 16.41 µs, corresponding to a maximum frame rate exceeding 60 kHz, and achieves diffraction-limited spatial resolution. Additionally, we show the ability to image vortex modes generated by 3D-printed phase plates, further demonstrating the system’s versatility. This approach provides a pathway for high-speed and highresolution mmWave imaging, with potential applications in security, communications, and scientific research.

DOI
10.1117/12.3042376

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Photonics Research•Mar 10, 2026•3 citations
We present a millimeter-wave imaging system based on fluorescence induced by Autler-Townes splitting in a four-level atomic Rydberg system. By employing counter-propagating probe and coupling beams, we create a plane of atoms in a dark state that is sensitive to incident mmWaves at 91.4 GHz. Objects placed in the mmWave beam path diffract the beam which, when imaged onto the cell using a PTFE lens, induce AT splitting in regions of higher intensity, increasing 780 nm fluorescence at 780 nm. Imaging this fluorescence with an optical camera effectively images the incident mmWave field. The system demonstrates a temporal response time of 16.41 µs, corresponding to a maximum frame rate exceeding 60 kHz, and achieves diffraction-limited spatial resolution. Additionally, we show the ability to image vortex modes generated by 3D-printed phase plates, further demonstrating the system’s versatility. This approach provides a pathway for high-speed and highresolution mmWave imaging, with potential applications in security, communications, and scientific research.
We demonstrate millimeter wave (mmWave) imaging using Autler-Townes (AT) splitting-induced fluorescence in rubidium vapor. By employing counter-propagating probe and coupling beams, we create a plane of atoms in a dark state that is sensitive to incident mmWave and demonstrate the method with mmWaves resonant with the transition between two neighboring Rydberg states at 91.4 GHz. Objects in the mmWave’s path affect the spatial profile of the mmWave field, which, in turn, leads to spatial variation of optical fluorescence at 780 nm. This results in a transduction of the mmWave spatial profile to an optical image that can be acquired by a CCD camera. We demonstrate real-time, diffraction-limited mmWave imaging in transmission geometry, over an effective sensing area of 6.5 cm 2 with a minimum 600 µV /cm detectable electric field and a rapid 16.4 µs response time. In addition, we demonstrate this method with a variety of imaging masks, including 3D-printed vortex phase plates. Our study provides a pathway for high-speed and high-resolution mmWave imaging with potential applications in security, communications, and scientific research.
We demonstrate a spatially resolved method for imaging millimeter-wave (mmWave) electric fields using Rydberg-state fluorescence in a warm atomic vapor. By utilizing a multi-photon ladder excitation scheme, we leverage a specific decay channel that remains dark in the absence of the mmWave field, resulting in high-contrast imaging with effectively zero background. Absolute calibration of the local electric field is achieved by reconstructing the Autler-Townes splitting of the Rydberg resonance across the imaging volume. To ensure robust field extraction across a wide dynamic range-including regimes where spectral features are not fully resolved-we employ a steady-state analysis based on the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation. We apply this technique to visualize standing-wave interference patterns within a vapor cell and demonstrate the ability to engineer local field distributions using structured dielectric reflectors. This approach provides a versatile and self-calibrating platform for the diagnostic imaging of high-frequency electromagnetic fields and the characterization of mmWave-optical interfaces.
In this paper, we demonstrate the detection of millimeter waves via Autler-Townes splitting in 85Rb Rydberg atoms. This method may provide an independent, atom-based, SI-traceable method for measuring mm-wave electric fields, which addresses a gap in current calibration techniques in the mm-wave regime. The electric-field amplitude within a rubidium vapor cell in the WR-10 wave guide band is measured for frequencies of 93.71 GHz and 104.77 GHz. Relevant aspects of Autler-Townes splitting originating from a four-level electromagnetically induced transparency scheme are discussed. We measured the E-field generated by an open-ended waveguide using this technique. Experimental results are compared to a full-wave finite element simulation.
We discuss a fundamentally new method for electric (E) field strength (V/m) metrology applicable to the near-field. This new approach is significantly different from currently used field measurement techniques in that it is based on the interaction of radio-frequency (RF) E-fields with Rydberg atoms (alkali atoms placed in a glass vapor cell that are excited optically to Rydberg states). The applied RF E-field alters the state of the atoms. The Rydberg atoms act like an RF-to-optical transducer, converting an RF E-field strength to an optical-frequency response. In this new approach, we employ the phenomena of electromagnetically induced transparency (EIT) and Autler-Townes splitting. The RF transition in the four-level atomic system causes a split of the EIT transmission spectrum of a probe laser into two peaks. This splitting is easily measured and is directly proportional to the applied RF E-field amplitude. The significant dipole response of Rydberg atoms enables this technique to make self-calibrating measurements over a large frequency band including 500 MHz to 500 GHz (and possibly up to 1 THz and down to 10s of megahertz). In this paper, we report on our results in the development of this metrology approach, including the first fiber-coupled vapor-cell for E-field measurements. We also discuss key applications, including self-calibrated measurements, millimeter-wave and sub-THz measurements, field mapping, and sub-wavelength and near-field imaging. We show results for mapping the fields inside vapor cells, for measuring the E-field distribution along the surface of a circuit board, and for measuring the near-field at the aperture in a cavity. We also discuss the uncertainties of this measurement technique.
We present a technique for measuring radio-frequency (RF) electric field strengths with sub-wavelength resolution. We use Rydberg states of rubidium atoms to probe the RF field. The RF field causes an energy splitting of the Rydberg states via the Autler-Townes effect, and we detect the splitting via electromagnetically induced transparency (EIT). We use this technique to measure the electric field distribution inside a glass cylinder with applied RF fields at 17.04 GHz and 104.77 GHz. We achieve a spatial resolution of ≈100 μm, limited by the widths of the laser beams utilized for the EIT spectroscopy. We numerically simulate the fields in the glass cylinder and find good agreement with the measured fields. Our results suggest that this technique could be applied to image fields on a small spatial scale over a large range of frequencies, up into the sub-terahertz regime.
Terahertz imaging has become increasingly important across various fields and practical production applications. Achieving both high sensitivity and high speed remains a primary challenge for most current THz imaging technologies. In this work, we present an imaging system based on Rydberg atomic vapor operating at frequencies exceeding 1 THz. By utilizing Cesium 133 atoms coupled with THz waves, de-excitation radiation generated after atomic excitation to Rydberg states converts invisible THz waves into visible light, enabling the acquisition of spatial information and intensity distributions of THz fields. The system achieves a minimum detectable power of 330 fW /s 1/2 per (2.4×2.4) μm 2 , an imaging resolution of approximately 1.7 mm, and an imaging bandwidth of 8.6 MHz. Additionally, the theoretical imaging rate can exceed 1 MHz. The Rydberg-atom-based THz imaging system exhibits a simple structure and is amenable to miniaturization. This THz imaging method holds promise for advancing applications in THz nondestructive testing, biomedical imaging, and concealed object detection.