Fourier-domain OCT with undetected mid-infrared photons in the high-gain regime

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