Light-field microscopy with correlated beams for high-resolution volumetric imaging

Abstract

Light-field microscopy represents a promising solution for microscopic volumetric imaging, thanks to its capability to encode information on multiple planes in a single acquisition. This is achieved through its peculiar simultaneous capture of information on light spatial distribution and propagation direction. However, state-of-the-art light-field microscopes suffer from a detrimental loss of spatial resolution compared to standard microscopes. In this article, we experimentally demonstrate the working principle of a new scheme, called Correlation Light-field Microscopy (CLM), where the correlation between two light beams is exploited to achieve volumetric imaging with a resolution that is only limited by diffraction. In CLM, a correlation image is obtained by measuring intensity correlations between a large number of pairs of ultra-short frames; each pair of frames is illuminated by the two correlated beams, and is exposed for a time comparable with the source coherence time. We experimentally show the capability of CLM to recover the information contained in out-of-focus planes within three-dimensional test targets and biomedical phantoms. In particular, we demonstrate the improvement of the depth of field enabled by CLM with respect to a conventional microscope characterized by the same resolution. Moreover, the multiple perspectives contained in a single correlation image enable reconstructing over 50 distinguishable transverse planes within a 1 mm3 sample.

Correlated-photon imaging at 10 volumetric images per second

“…Adopting chaotic light illumination entails that the magnitude of the correlation function ( 1 ) scales like the product on the mean number of photons 44 , thus being crucial in ensuring that correlation measurements provide analogous results both in the case of high-intensity, as in Ref. 38 , and in the single-photon regime, as in the present work. However, a key requirement in this sense, is that the SPAD array works in the linear regime (namely, the probability to detect a photon is proportional to the intensity of the impinging field), far from saturation.…”

“…Such classically correlated sources typically entails a worse signal-to-noise ratio (SNR) than expected with entangled photons 18 , 19 , but also brings in several practical advantages: light sources are simpler and more feasible (potentially, any available incoherent source could serve the purpose 20 , 21 ), the image acquisition time can be significantly reduced by avoiding the low production rate of entangled photons, and protocols are potentially insensitive to the deleterious effects of decoherence. A wide range of quantum-inspired imaging protocols based on chaotic light correlations have been demonstrated so far, in different application scenarios: imaging of objects hidden to the main sensor 22 , 23 , dual wavelength imaging 24 , 25 (analogous to the implementation with entangled photons 26 , 27 ), detection of objects surrounded by turbulence 28 – 30 , 3D imaging through computational ghost imaging 31 , refocusing and 3D imaging through correlation plenotpic imaging and microscopy 32 – 38 .…”

“…Such a challenge is intrinsic to this approach, since evaluating correlation functions requires sampling a high enough number of statistical realizations. The use of high-resolution CCD and CMOS cameras in correlation imaging setups 6 , 7 , 13 , 16 , 34 , 38 , 39 has enabled to overcome the extremely time-consuming mechanical scanning of the image plane, as performed in pioneering correlation imaging experiments 3 , 14 , 17 . There are two time scales that one must consider when dealing with the speed of correlation imaging with a camera 7 .…”

Quantum-enhanced plenoptic imaging

“…In fact, CPI can work with chaotic illumination (κ = 1), with a source of entangled photons (κ = 0), 13,14 and, in principle, with any other source of correlated particles. An addition to the versatility of the technique, the basic principle of correlating two detectors with spatial resolution to retrieve light-field information can be applied to microscopy 12,15 as well as photography.…”