Mid-infrared frequency-domain optical coherence tomography with undetected photons

Optical coherence tomography (OCT) is a well-established widely used non-invasive imaging technique that provides morphological information of sub-surface structures of the materials. This technique has found extensive use in biomedical imaging, particularly in acquiring 3D images of the human retina using near-infrared (near-IR) light. However, for non-destructive testing of strongly scattering materials such as ceramics and paint, OCT in the mid-IR range remains a challenge due to the lack of efficient detectors and cost-effective light sources. In this contribution, we summarize results on a novel approach to overcome these limitations using nonlinear interferometry based on quantum interference and correlated photon pairs, which we refer to as” OCT with undetected photons”. We present an overview and the working principle and the implementation of this technique, which can offer significant advantages over previous time-domain implementations in terms of signal-to-noise ratio, stability, and speed as well as axial resolution reaching 10 µm. Moreover, our efficient detection requires only very low power levels of 200 pW on the sample, making it suitable for very sensitive biological samples or sensitive art works. In contrast, classical approaches use 20 mW, which is 108 times more. We demonstrate the applicability of our approach by scanning ceramics, which are materials of high practical relevance, and obtaining convincing images of these samples. We conclude from results that there are distinct advantages over classical approaches to mid-IR OCT, while being much simpler in terms of source and detection technology. Our results show that OCT with undetected photons is now a practical technology ready to enter commercial development.

References:

[1] A. Vanselow, et.al., Optics Letters 44(19), 4638–4641 (2019)
[2] A. Vanselow, et.al., Optica 7(12), 1729–1736 (2020)