Abstract
Low-light-level imaging techniques have application in many diverse fields, ranging from biological sciences to security. A high-quality digital camera based on a multi-megapixel array will typically record an image by collecting of order 105 photons per pixel, but by how much could this photon flux be reduced? In this work we demonstrate a single-photon imaging system based on a time-gated intensified camera from which the image of an object can be inferred from very few detected photons. We show that a ghost-imaging configuration, where the image is obtained from photons that have never interacted with the object, is a useful approach for obtaining images with high signal-to-noise ratios. The use of heralded single photons ensures that the background counts can be virtually eliminated from the recorded images. By applying principles of image compression and associated image reconstruction, we obtain high-quality images of objects from raw data formed from an average of fewer than one detected photon per image pixel.
Highlights
Low-light-level imaging techniques have application in many diverse fields, ranging from biological sciences to security
We use correlated photons generated by spontaneous parametric downconversion (SPDC) and a multipixel intensified CCD camera (ICCD) triggered by a single-photon avalanche detector (SPAD), the latter acting as the heralding detector
The generated near-collinear beam of frequency-degenerate, downconverted photons is selected through the use of high-transmission interference filters with a 10 nm bandwidth centred on 710 nm
Summary
Our camera-enabled, time-gated imaging system uses the detection of one of the photons, the ‘heralding’ photon, from a downconverted photon pair by a single-pixel detector, to trigger the detection of the position-correlated photon by an intensified CCD camera (ICCD) We characterize this imaging system for two different system configurations, either with the object in the heralding arm, as per GI, or the object in the camera arm of the system. To utilize the low-photon flux capabilities of our system, reconstruction techniques are applied to our data that allow us to obtain images using undersampled data sets consisting of an average of fewer than one photon per image pixel We achieve this by operating within the constraints of Poissonian statistics and exploiting the sparsity of our images in the spatial frequency domain to subjectively improve the quality of the reconstructed images. This minimization of photon exposure may have application to covert imaging applications or where the light itself can damage or otherwise modify the object
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