Quantum technology promises improvements in imaging, computing, and communication, for example using the resource of entanglement between photons with spatial correlations. Detecting spatial correlations, or coincidences, between entangled photons scalably, efficiently, and affordably is therefore an essential capability. However, this task is non-trivial for existing camera technologies, which require low illumination intensities or low detection duty cycles to count coincidences at high signal-to-noise ratios, resulting in long acquisition time, or use expensive custom electronic components. Here, we present an entanglement imaging system based around a novel Single-Photon Avalanche Diode (SPAD) array camera, optimized for sparse illumination with correlated photon pairs. The system is capable of maintaining a duty cycle close to 100%, while simultaneously detecting spatially resolved coincidences with high SNR, enabling the acquisition of real-time entanglement videos at a ~Hz frame rate. We use our system to demonstrate real-time monitoring of entanglement interference visibility, optical system point spread function, as well as real-time widefield entanglement-enhanced phase imaging. Our results show that SPAD array cameras represent a natural choice for scalable entanglement detection and imaging applications.
Recently, a set of polarimetric indicators, the Indices of Polarimetric Purity (IPPs), were described in the literature. These indicators allow synthesize depolarization content of samples, and provide further analysis of depolarizers than other existing polarimetric indicators. We demonstrate the potential of the IPPs as a criterion to characterize and classify depolarizing samples. In particular, the method is firstly analyzed through a series of basic polarization experiments, and we prove how differences in the depolarizing capability of samples, concealed from the commonly used depolarization index PΔ, are identified with the IPPs.
In the second part of this work, the method is experimentally highlighted by studying a rabbit leg ex-vivo sample. The obtained images of the ex-vivo sample illustrate how IPPs provide a significant enhancement in the image contrast of some biological tissues and, in some cases, present new information hidden in the usual polarimetric channels. Moreover, new physical interpretation of the sample can be derived from the IPPs which allow us to synthesize the depolarization behavior.
Finally, we also propose a pseudo-colored encoding of the IPPs information that provides an improved visualization of the samples. This last technique opens the possibility to highlight a specific tissue structure by properly adjusting the pseudo-colored formula.
We highlight the interest of using the Indices of Polarimetric Purity (IPPs) for the biological tissue inspection. These are three polarimetric metrics focused on the study of the depolarizing behaviour of the sample. The IPPs have been recently proposed in the literature and provide different and synthetized information than the commonly used depolarizing indices, as depolarization index (PΔ) or depolarization power (Δ). Compared with the standard polarimetric images of biological samples, IPPs enhance the contrast between different tissues of the sample and show differences between similar tissues which are not observed using the other standard techniques. Moreover, they present further physical information related to the depolarization mechanisms inherent to different tissues. In addition, the algorithm does not require advanced calculations (as in the case of polar decompositions), being the indices of polarimetric purity fast and easy to implement. We also propose a pseudo-coloured image method which encodes the sample information as a function of the different indices weights. These images allow us to customize the visualization of samples and to highlight certain of their constitutive structures. The interest and potential of the IPP approach are experimentally illustrated throughout the manuscript by comparing polarimetric images of different ex-vivo samples obtained with standard polarimetric methods with those obtained from the IPPs analysis. Enhanced contrast and retrieval of new information are experimentally obtained from the different IPP based images.
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