Interference effects in quantum-optical coherence tomography using spectrally engineered photon pairs

TL;DR

This paper extends the theoretical framework of quantum-optical coherence tomography (QOCT) to include photon pairs with arbitrary spectral correlations and demonstrates how pump bandwidth influences interference effects, offering practical insights for QOCT applications.

Contribution

It introduces a generalized model of QOCT that accounts for various spectral correlations and experimentally investigates the impact of pump bandwidth on interference patterns.

Findings

Spectral correlations in photon pairs affect interference in QOCT.

Increasing pump bandwidth can suppress cross-correlation interference effects.

Experimental results align with the extended theoretical model.

Abstract

Optical-coherence tomography (OCT) is a technique that employs light in order to measure the internal structure of semi-transparent, e.g. biological, samples. It is based on the interference pattern of low-coherence light. Quantum-OCT (QOCT), instead, employs the correlation properties of entangled photon pairs, for example, generated by the process of spontaneous parametric downconversion (SPDC). The usual QOCT scheme uses photon pairs characterised by a joint-spectral amplitude with strict spectral anti-correlations. It has been shown that, in contrast with its classical counterpart, QOCT provides resolution enhancement and dispersion cancellation. In this paper, we revisit the theory of QOCT and extend the theoretical model so as to include photon pairs with arbitrary spectral correlations. We present experimental results that complement the theory and explain the physical underpinnings appearing in the interference pattern. In our experiment, we utilize a pump for the SPDC process ranging from continuous wave to pulsed in the femtosecond regime, and show that cross-correlation interference effects appearing for each pair of layers may be directly suppressed for a sufficiently large pump bandwidth. Our results provide insights and strategies that could guide practical implementations of QOCT.