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arXiv:2608.20015

Wide-field mid- to long-wave infrared imaging with undetected photons

Vladimir Kornienko, Nathan Gemmell, Caiyi Liu, Asteria Chen, Chris Phillips, Rupert Oulton

quant-phphysics.opticsSubmitted Aug 20, 2026• Announced Aug 21, 2026• 0 citations
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Abstract

Quantum imaging with undetected photons (QIUP) allows an object to be probed at mid-infrared frequencies by only measuring interference in the visible range, thus leveraging silicon camera technology. We show that non-collinear phase-matching in a silver thiogallate (AgGaS$_2$) crystal enables wide-field QIUP in the wavelength range of 6-10 $μ$m (1670-1000 cm$^{-1}$). A combination of coherent detection and infrared photons being ``undetected'' enables imaging at ${\sim}$100 times better than the background-limited infrared photodetection (BLIP) limit. At 8 $μ$m, our images have over 8000 $\pm$ 100 resolvable elements with a 297 $\pm$ 5 $μ$m resolution, and 10 s acquisition time. Our results pave the way to fast, background-noise-free, room-temperature, spectrally-selective mid-infrared imaging.

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6 pages, 4 figures

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Quantum imaging with undetected photons (QIUP) allows an object to be probed at mid-infrared frequencies by only measuring interference in the visible range, thus leveraging silicon camera technology. We show that non-collinear phase-matching in a silver thiogallate (AgGaS2_22​) crystal enables wide-field QIUP in the wavelength range of 6-10 μμμm (1670-1000 cm−1^{-1}−1). A combination of coherent detection and infrared photons being ``undetected'' enables imaging at ∼{\sim}∼100 times better than the background-limited infrared photodetection (BLIP) limit. At 8 μμμm, our images have over 8000 ±\pm± 100 resolvable elements with a 297 ±\pm± 5 μμμm resolution, and 10 s acquisition time. Our results pave the way to fast, background-noise-free, room-temperature, spectrally-selective mid-infrared imaging.
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.
Quantum imaging with undetected photons (QIUP) is an active imaging method in which the detected and the probing photons are distinct and can be selected from different spectral regions. This technique holds potential for a wide range of applications affected by the trade-off between illumination wavelength and detection efficiency. The state-of-the-art experimental configurations assess the spectral absorption and phase information of a target solely in a transmissive configuration, which presents a limitation for applications where the target cannot be aligned with optical elements positioned behind it. In this work, we present an experimental configuration for QIUP of a scattering target, aiming to fill the gap in the applicability of the QIUP technique and enabling QIUP to detect remote targets.
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Sensing with undetected photons has become a vibrant, application-driven research domain with a special focus on the mid-infrared (mid-IR) wavelength region. Since the mid-IR contains spectral bands with highly specific and strong molecular absorbance signatures, often referred to as fingerprints, a multitude of different samples and their compositions can be detected and quantified spectroscopically. Enhancing this spectroscopic method with imaging capabilities leads to a powerful technique for environmental monitoring and biomedical applications that enables automated diagnostics while omitting time-consuming and non-reversible labeling steps. To evade the shortcomings of state-of-the-art instruments for mid-IR hyperspectral microscopy—namely cost, complexity, power consumption, and performance, which stem from technological challenges in mid-IR detection and light sources—we construct a proof-of-concept nonlinear interferometer in a wide-field imaging arrangement. This nominally narrowband imaging technique is then expanded to acquire broadband spectral information through capturing images for varying interferometer displacement and applying a pixelwise Fourier-transform of the resulting interferograms, yielding high-resolution infrared spectra for each camera pixel. For the broadband range of 2300−3100cm −1 , covering the important CH-stretch band, we perform hyperspectral imaging that simultaneously resolves 3500 spatial modes, each with a spectral resolution of 10cm −1 , leveraging in total around 10 5 spatio-spectrally entangled photon modes. Our image acquisition uses a commercial sCMOS camera, while a medium-power and compact continuous-wave pump laser is the only necessary light source. For a moderate speed of 360 voxel/s, we obtain a predominantly shot-noise-influenced signal-to-noise ratio (SNR) of 50. We further demonstrate the practicality of our novel hyperspectral imaging technique for microplastics detection and bio-imaging tasks and outline engineering solutions to increase its speed by several orders of magnitude. This shows that our quantum imaging technique is highly promising for applications requiring compact, cost-effective label-free analyses.
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