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arXiv:2505.04490

Mid-infrared quantum scanning microscopy via visible light beyond spatial correlations

Josué Ricardo León-Torres, Vasile-Laurenţiu Dosan, M. M. Ćurčić, Alek Lagarrigue, Frank Setzpfandt, Markus Gräfe, Valerio Flavio Gili

Published May 7, 2025• 0 citations
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Abstract

The mid-infrared (MIR) region of the electromagnetic spectrum spans from 2- to 25-$μ\mathrm{m}$, serving as a valuable tool for accessing rich chemical information. Functional groups, lipids, and other complex molecules can be analyzed by optical absorption measurements due to their vibrational modes in the MIR spectral region. Over the past few decades, this field has faced challenges due to difficulties in generating MIR light and the limited maturity of detection systems in this spectral range. Quantum imaging with undetected light (QIUL) provides a spectrally tuneable photon-pair source, in which the sample can be illuminated with MIR light while visible (VIS) light is employed for detection and image reconstruction, overcoming the detection limitations and benefiting from the rich chemical information of the MIR spectral region. All previous QIUL implementations are based on spatial correlations, which are never perfect and thus hindered the imaging performance. In this work, we implement a raster-scanning QIUL method that is independent of the strength of the spatial correlations and achieves a spatial resolution beyond the limitations of these correlations.

DOI
10.48550/arxiv.2505.04490

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The mid-infrared (MIR) region of the electromagnetic spectrum spans from 2- to 25-μmμ\mathrm{m}μm, serving as a valuable tool for accessing rich chemical information. Functional groups, lipids, and other complex molecules can be analyzed by optical absorption measurements due to their vibrational modes in the MIR spectral region. Over the past few decades, this field has faced challenges due to difficulties in generating MIR light and the limited maturity of detection systems in this spectral range. Quantum imaging with undetected light (QIUL) provides a spectrally tuneable photon-pair source, in which the sample can be illuminated with MIR light while visible (VIS) light is employed for detection and image reconstruction, overcoming the detection limitations and benefiting from the rich chemical information of the MIR spectral region. All previous QIUL implementations are based on spatial correlations, which are never perfect and thus hindered the imaging performance. In this work, we implement a raster-scanning QIUL method that is independent of the strength of the spatial correlations and achieves a spatial resolution beyond the limitations of these correlations.
ABSTRACT The mid‐infrared (MIR) spectral region, spanning from 2‐ to 25‐, provides access to rich chemical information through the vibrational modes of functional groups, lipids, and other complex molecules. However, conventional imaging in this range remains limited by challenges in generating MIR light and by the lack of mature detection technologies. Quantum imaging with undetected light (QIUL) offers an alternative approach by using photon‐pair sources in which the sample is illuminated with MIR light while detection and image reconstruction are carried out at visible wavelengths. We report the first QIUL technique that achieves diffraction‐limited resolution without relying on spatial correlations of the photon‐pair, thereby overcoming a fundamental limitation of all previous implementations. This work establishes induced coherence without induced emission as the essential physical resource underlying QIUL and redefines its operational boundary, extending its applicability to regimes where spatial correlations are weak or absent. Our results represent a conceptual advance in quantum imaging and open the way toward practical and cost‐effective MIR microscopy based on visible detection.
Laser scanning microscopy (LSM) is known to be the workhorse for modern life-science, it allows to get new insights into a variety of biological processes. LSM together with illumination in the mid infrared region (Mid-IR) permits to map the chemical composition of samples to a space frame. However, low-light observations in the Mid-IR spectrum are still challenging and a limiting factor for a faster development. A label-free quantum scanning imaging system is presented here, capable of performing the detection in the visible regime, while the illumination is carried out in the Mid-IR region. Our quantum imaging with undetected light implementation aims to retrieve amplitude and phase images of biological samples containing a variety of functional groups that are present in the Mid-IR region
Infrared (IR) sensing has a significant potential in applications ranging from cellular imaging to environmental sciences [1]. A primary challenge in the field has been the lack of efficient IR detectors. Quantum imaging with undetected light (QIUL) [2] is a new powerful imaging tool. QIUL relies on the nonlinear interferometry, using induced coherence [3], which allows the spectral separation of sensing and detection, facilitating imaging in hard-to-access spectral regions like ultraviolet or IR. These spectral regions contain relevant information for the identification of protein, lipid, and nucleic acid content [1], [4]. The core of our work involves the design, construction, and characterization of a quantum light engine tailored for scanning microscopy with undetected light, presenting a ready-to-use implementation of a ground-breaking approach to overcome the limitations of traditional IR sensing technologies while using low illumination regime.
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Quantum imaging with undetected photons (QIUP) has recently emerged as a new powerful imaging tool. Exploiting the spatial entanglement of photon pairs, it allows decoupling of the sensing and detection wavelengths, facilitating imaging in otherwise challenging spectral regions by leveraging mature silicon-based detection technology. All existing implementations of QIUP have so far utilised the momentum correlations within the biphoton states produced by spontaneous parametric downconversion. Here, for the first time, we implement and examine theoretically and numerically the complementary scenario - utilising the tight position correlations formed within photon pairs at birth. This image plane arrangement facilitates high resolution imaging with comparative experimental ease, and we experimentally show resolutions below 10 μm at a sensing wavelength of 3.7 μm. Moreover, we present a quantitative numerical model predicting the imaging capabilities of QIUP for a wide range of parameters. Finally, by imaging mouse heart tissue at the mid-IR to reveal morphological features on the cellular level, we further demonstrate the viability of this technique for the life sciences. These results offer new perspectives on the capabilities of QIUP for label-free widefield mid-IR microscopy, enabling real-world biomedical as well as industrial imaging applications.