Sub-second A-scan Acquisition Using Marginal Spectral-Domain Quantum Optical Coherence Tomography

TL;DR

This work tackles the slow acquisition challenge in quantum optical coherence tomography (QOCT) by introducing marginal spectral-domain QOCT (M-SD-QOCT), which extracts a full A-scan from a single marginal interferogram $p_c(\tau_0,\omega_i)$ without mechanical scanning. By using a high-flux SPDC source around $810~\text{nm}$ and a diffraction-grating/ICCD spectrometer, the authors record a marginal interference pattern and obtain the A-scan via a fast FFT, achieving sub-second times (down to $t_{acq}=0.1~\text{s}$ for a mirror) and a 4 mm penetration depth. The method shows excellent agreement with theory, and the axial resolution is currently limited by the ~1 nm SPDC bandwidth but can be improved with broader sources (e.g., type-0 PPKTP or type-I BBO). This approach advances SD-QOCT toward practical biomedical imaging, offering rapid, non-scanning, depth-resolved measurements with competitive resolution and depth performance.

Abstract

We report an optimized implementation of spectral-domain quantum optical coherence tomography (SD-QOCT) capable of acquiring axial scans (A-scans) of multilayer samples without in the absence of mechanical scanning, at an unprecedented speed. We demonstrate a proof-of-concept system that integrates a diffraction grating, a high-resolution intensified CCD camera, and a high-flux photon-pair source operating in the VIS-NIR region (810 nm). This configuration enables the acquisition of an entire marginal SD-QOCT interferogram in a single camera exposure, yielding a transverse A-scan with a record acquisition time of 100 ms and a penetration depth of 4 mm. The measured interferometric response shows excellent agreement with the theoretical model. These results represent a decisive step toward the practical deployment of SD-QOCT as a competitive imaging modality for biomedical applications.

Figures (5)

• Figure 1: Schematics of the marginal SD-QOCT technique. The ICCD camera records the marginal interferogram $p_c(\tau_0,\omega_i)$ with record acquisition times, for a fixed signal--idler temporal delay $\tau_0$ selected at the reference mirror according to a specific criterion (see main text). Applying a fast Fourier transform to this marginal distribution yields the temproal-domain interferogram $p_c(\tau_0,t)$, which directly reveals the A-scan of the sample.
• Figure 2: Experimental setup for the marginal SD-QOCT scheme, see text for description.
• Figure 3: a) SD-QOCT interferogram for a mirror, with the corresponding time-domain interferogram (FFT) shown in panel b. The inset on the left of panel a illustrates a representative fixed-delay, single-exposure measurement of the marginal interferogram, acquired with a 10 s ICCD exposure at the temporal-delay value indicated by the dashed green line; its FFT is displayed in the left inset of panel b. Panels c and d present the corresponding numerical simulations. Panel e compares the TD-QOCT interferogram obtained from direct coincidence measurements (red dots), by integrating over frequency the experimental 2D interferogram in panel a (black dots), and similarly for the numerically-obtained 2D interferogram in panel c (blue curve).
• Figure 4: a) SD-QOCT interferogram for the 1 mm glass slide, with the corresponding time-domain interferogram (FFT) shown in panel b. The sideplot in panel a illustrates a representative fixed-delay marginal interferogram, acquired with a 10 s ICCD exposure at the temporal-delay value indicated by the dashed green line; its FFT is displayed in the sideplot of panel b. Panels c and d present the corresponding numerical simulations. Panel e compares the TD-QOCT interferogram obtained from direct coincidence measurements (red dots), by integrating over frequency the experimental interferogram in panel a (black dots), and the theoretical interferogram in panel c (blue curve). The colored labels in panels b, d, and e correspond to the distinct reflective layers and artifact features of the sample (see text for details).
• Figure 5: Measurements of the marginal SD-QOCT interferogram $P_c(\tau_0,\omega_i)$ obtained at a fixed delay value in a single camera exposure: a) mirror sample, acquired with a 0.1 s ICCD integration time, and b) 1 mm glass slide, acquired with a 10 s integration time. The lower panels show the corresponding FFTs, revealing the reflective surface of the mirror in panel c and the two interfaces of the glass slide in panel d, together with a schematic representation of the sample. The blue curves in all four panels show the numerical simulations, which exhibit excellent agreement with the experimental data.