Swept-source optical coherence tomography based on a backward terahertz-wave parametric oscillator achieving depth super-resolution

An approach in the generation of wide and continuously frequency tunable terahertz (THz) waves by quasi-collinear phase-matching (QCPM) control in a backward THz-wave parametric oscillator (BW-TPO) and its application to THz-wave swept-source optical coherence tomography (THz-SS-OCT) is reported. The narrow THz-wave linewidth of the BW-TPO source (<6 GHz) ensures stable, mode-hop free oscillation along its coherence length (≈20 mm), suitable for interferometry applications. The THz-wave tuning characteristics (0.26-0.80 THz) and corresponding depth resolution (≈0.8 mm) of the THz-SS-OCT system are described. A super-resolution technique based on an annihilating filter method was employed for depth resolution enhancement down to 0.013 mm, which is the best depth resolution among all conventional THz-SS-OCT systems. Our work demonstrates, to the best of our knowledge, the first THz-SS-OCT system based on a BW-TPO and its applications in semiconductor thickness measurement and depth-profiling.