Fourier-domain OCT with undetected\nmid-infrared photons in the high-gain\nregime

I present the first experimental implementation for Fourier-domain optical coherence
\ntomography (OCT) using undetected mid-infrared photons in the high-gain regime. The
\ncore component is a custom-designed, aperiodically poled Potassium Titanyl Phosphate
\n(KTiOPO4) crystal, enabling broadband parametric down-conversion (PDC) with high
\namplification. After discussing the theoretical background of classical OCT, nonlinear
\nprocesses, PDC, and interference with undetected photons, I report the experimental
\nperformance of my setup. It achieves a typical signal-to-noise ratio (SNR) of ≈ 40 dB,
\naxial resolution of ≈ 30 μm, depth range of ≈ 320 μm, and macroscopic lateral resolution
\nof ≈ 3.3 mm. I demonstrate the setup’s capability to resolve real microstructures and
\nits advantage over classical OCT in operating with samples obscured by a Germanium
\nwindow. Additionally, I confirm the high-gain regime’s potential for strong signal power,
\nallowing detection with standard Si power meters and time-gated measurements.