*Important notice: This news reports on an unedited version of an accepted paper and is awaiting final editing. Therefore, the paper should not be regarded as conclusive or treated as established information.
Quantum optical coherence tomography (QOCT) provides high-resolution, dispersion-immune imaging but has been limited by slow image acquisition times. A recent study published in Scientific Reports demonstrated an optimized marginal spectral-domain QOCT system capable of acquiring axial scans in just 100 milliseconds without mechanical scanning. This approach enables rapid, accurate generation of depth profiles while preserving the advantages of QOCT and addressing the limitations of conventional systems.
Study: Sub-second a-scan acquisition using marginal spectral-domain quantum optical coherence tomography. Image Credit: Vink Fan /Shutterstock.com
Advancements in Quantum Imaging Technology
Optical coherence tomography (OCT) is widely used for high-resolution, noninvasive imaging of optical scattering media. Conventional OCT relies on low-coherence light sources, but image quality can be degraded by dispersion in complex samples.
QOCT addresses these limitations by using frequency-correlated entangled photon pairs rather than classical light, thereby providing immunity to even-order dispersion and improving axial resolution.
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Despite these advantages, conventional time-domain QOCT has remained impractical for many applications due to slow image acquisition caused by low photon flux and the need for mechanical scanning stages. This limitation has motivated the development of faster spectral-domain approaches that eliminate moving components.
Novel Design: Mechanical-Free Tomography Framework
To overcome mechanical scanning challenges, researchers developed a proof-of-concept marginal spectral-domain quantum optical coherence tomography (SD-QOCT) system.
The setup used a high-flux entangled-photon source generated via spontaneous parametric down-conversion (SPDC) in a 10 mm type-II periodically poled potassium titanyl phosphate (PPKTP) crystal. This crystal was then pumped by a 1 mW continuous-wave laser at 405 nm, producing cross-polarized photon pairs centered at 810 nm.
In this system, one photon interacted with the sample while the other traveled through the reference arm, and the two beams then interfered at a polarizing beamsplitter. Instead of resolving both photons, the system resolved only one using a diffraction grating and a high-resolution intensified charge-coupled device (ICCD) camera. In contrast, the complementary photon was collected by a high-efficiency avalanche photodiode acting as a bucket detector.
Detection of the bucket photon triggered the ICCD, enabling the complete spectral interferogram. This also allowed the recording of a full axial profile in a single camera exposure at a fixed optical delay. This design also eliminated the need for mechanical scanning and other time-consuming processes, thereby reducing acquisition time and costs.
Performance: Speed and Penetration Depth
The optimized SD-QOCT system significantly improved imaging speed. A complete axial scan of a reflective mirror was acquired in just 100 milliseconds, while imaging a 1 mm thick glass coverslip required only 10 seconds. These acquisition times demonstrate that rapid, single-exposure quantum optical coherence tomography is feasible without scanning.
The system also showed strong imaging performance. It achieved a penetration depth of about 4 mm, the deepest reported for this SD-QOCT approach, with a spectral resolution of about 0.05 nm across a usable bandwidth of approximately 15 nm. The experimental measurements closely matched theoretical simulations, accurately resolving the reflective interfaces of the glass sample together with the expected quantum interference artifacts.
The current prototype achieved an axial resolution of approximately 500 μm. Researchers related this to the deliberately narrow emission bandwidth of the SPDC source, which was selected to maximize photon flux rather than spatial resolution. This design increased the spectral power density, allowing the camera to reach saturation quickly and enabling single-shot image acquisition without grating rotations or mechanical scanning.
Applications: Optical Diagnostics in Various Fields
The rapid acquisition speed of the marginal spectral-domain SD-QOCT system broadens the potential applications of quantum optical imaging. Eliminating mechanical scanning also makes the technique more suitable for practical imaging systems.
In biomedical imaging, fast, dispersion-immune depth profiling could enhance examinations of multilayered biological tissues, where long acquisition times increase the risk of motion artifacts. However, further studies using biological samples are required.
Beyond healthcare, the system could prove useful for non-destructive testing of transparent and multilayered materials. Its ability to rapidly measure internal interfaces and layer thicknesses could support quality control in manufacturing optical components, thin-film coatings, and photonic devices, where fast, non-contact inspection is crucial.
Future Directions: Enhancing Quantum Tomography
This research demonstrates that marginal spectral-domain quantum optical coherence tomography can achieve high-speed imaging without mechanical scanning. By employing a high-flux entangled photon source with camera-based spectral detection, the system successfully acquired single-shot axial scans in as little as 100 milliseconds while achieving a penetration depth of approximately 4 mm.
Future work should focus on employing broader-bandwidth photon sources, such as type-0 PPKTP crystals, which could increase axial resolution to approximately 11 μm. Overall, combining these hardware advancements with computational methods for phase compensation and artifact removal could further improve image quality and facilitate faster quantum imaging systems for biomedical imaging and optical metrology.
Journal Reference
Yepiz-Graciano, P.D., et al. (2026). Sub-second a-scan acquisition using marginal spectral-domain quantum optical coherence tomography. Scientific Reports. https://www.nature.com/articles/s41598-026-60127-3.
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