Classical Ghost Imaging Research Articles

Universal mask for hard x rays

The penetrating power of x rays underpins important applications such as medical radiography. However, this same attribute makes it challenging to achieve flexible on-demand patterning of x-ray beams. One possible path to this goal is “ghost projection,” a method that may be viewed as a reversed form of classical ghost imaging. This technique employs multiple exposures of a single illuminated non-configurable mask that is transversely displaced to a number of specified positions to create any desired pattern. An experimental proof of concept is given for this idea, using hard x rays. The written pattern is arbitrary, up to a tunable constant offset, and its spatial resolution is limited by both (i) the finest features present in the illuminated mask and (ii) inaccuracies in mask positioning and mask exposure time. In principle, the method could be used to make a universal lithographic mask in the hard-x-ray regime. Ghost projection might also be used as a dynamically configurable beam-shaping element, namely, the hard-x-ray equivalent of a spatial light modulator. The underpinning principle can also be applied to gamma rays, neutrons, electrons, muons, and atomic beams. Our flexible approach to beam shaping gives a potentially useful means to manipulate such fields.

Optimizing nonconfigurable, transversely displaced masks for illumination patterns in classical ghost imaging

Classical ghost imaging is a new paradigm in imaging where the image of an object is not measured directly with a pixelated detector. Rather, the object is subject to a set of illumination patterns and the total interaction of the object, e.g., reflected or transmitted photons or particles, is measured for each pattern with a single-pixel or bucket detector. An image of the object is then computed through the correlation of each pattern and the corresponding bucket value. Assuming no prior knowledge of the object, the set of patterns used to compute the ghost image dictates the image quality. In the visible-light regime, programmable spatial light modulators (SLMs) can generate the illumination patterns. In many other regimes, such as x rays, electrons, and neutrons, no such dynamically configurable modulators exist, and patterns are commonly produced by employing a transversely translated mask. Moreover, in visible-light regimes, mask switching rates exceeding the fastest SLMs may often be achieved through transverse translation (e.g., rotation) of a nonconfigurable mask. In this simulations-based paper we explore some of the properties of masks or speckle that should be considered to maximize ghost-image quality, given a certain experimental classical ghost-imaging setup employing a transversely displaced but otherwise nonconfigurable mask.

Contribution of wave aberrations represented by Zernike polynomials to the cross-correlation function between distorted and actual speckle patterns

Speckles are sensitive to the slightest inhomogeneities of the medium, which is used in optical research methods such as speckle interferometry. However, the stochastic nature of propagation of speckle fields complicates their accurate detection and processing. For example, aberrations in the optical system result in the decorrelation of the image of speckles with the actual speckles that are observed in free space. The report will consider the main types of wave aberrations of optical system and their influence on the correlation properties of speckle patterns. The research results can be used to optimize optical systems in which speckles play a significant role, for example, in classical ghost imaging.

Experimental demonstration of ghost imaging with speckled light in long-wavelength infrared range

Infrared imaging with a single-pixel camera can achieve radiometric accuracy not currently available with multi-pixel thermal cameras. One of the actively investigated single-pixel camera technology is ghost imaging. We propose an optical design to experimentally demonstrate classical ghost imaging in the long-wave infrared frequency range with speckled light without using a spatial light modulator. We obtained an example low-quality ghost image and then used the cross-correlation function to identify and explain the main difficulties in ghost imaging with a thermal camera.

Classical Ghost Imaging: A Comparative Study of Algorithmic Performances for Image Reconstruction in Prospect of Plenoptic Imaging

Ghost Imaging has been extensively explored for 25 years for a two reasons: the rich physics of second-order photon correlations that enable this imaging scheme and the possibility of implementing new imaging protocols with interesting real-life applications, e.g. imaging in turbulent media, investigation of sensitive samples in low-flux regimes, 3-D plenoptic imaging, and so on. Since the first demonstration of Ghost Imaging, several extended versions of the Traditional Ghost Imaging algorithm have been proposed, such as Correspondence Ghost Imaging, Pseudo-Inverse Ghost Imaging, and normalization techniques that rely on different computational approaches to obtain the image from measured data. So far, a direct comparison of all above-mentioned protocols for the same experimental parameters is still lacking. In this work, we experimentally and numerically implement a number of different methods and systematically compare them in terms of the obtained SNR and computational cost. Furthermore, we investigate their compatibility with Correlation Plenoptic Imaging, a technique strictly connected to Ghost Imaging, that allows refocusing of images, increasing the depth of field (DOF) and making 3D visualization possible. Our results can provide useful guidelines for the choice of a suitable numerical algorithm for in the light of Ghost Imaging applications.

Inherent dose-reduction potential of classical ghost imaging

Classical ghost imaging is a computational imaging technique that employs patterned illumination. It is very similar in concept to the single-pixel camera in that an image may be reconstructed from a set of measurements even though all imaging quanta that pass through that sample are never recorded with a position resolving detector. The method was first conceived and applied for visible-wavelength photons and was subsequently translated to other probes such as x rays, atomic beams, electrons and neutrons. In the context of ghost imaging using penetrating probes that enable transmission measurement, we here consider several questions relating to the achievable signal-to-noise ratio (SNR). This is compared with the SNR for conventional imaging under scenarios of constant radiation dose and constant experiment time, considering both photon shot-noise and per-measurement electronic read-out noise. We show that inherent improved SNR capabilities of ghost imaging are limited to a subset of these scenarios and are actually due to increased dose (Fellgett advantage). An explanation is also presented for recent results published in the literature that are not consistent with these findings.

Ghost Mach–Zehnder interferometry for phase measurement with spatially incoherent light

We describe a phase-measuring interferometry based on classical ghost imaging with spatially incoherent light. The setup is constructed in such a way that a conventional Mach–Zehnder (MZ) interferometer is incorporated into the test arm of a standard classical ghost imaging setup. This technique may thus be referred to as ghost MZ interferometry. It is shown theoretically that the correlation between intensity fluctuations at two detectors gives an interference fringe pattern specifying the phase of the object. The features of the interference fringe pattern vary, depending on the type of the detector in the test arm and the quantities characterizing the imperfection of the setup. As a consequence, we demonstrate that correct phase imaging is possible with this technique even when the setup has a certain imperfection. The conditions for which the proposed ghost MZ interferometry works properly are addressed.

Aberration-insensitive microscopy using optical field-correlation imaging

The possibility to reduce the effect of optical aberrations has been proposed in several publications on classical ghost imaging. The two-armed ghost-imaging systems make use of spatially incoherent illumination and point-by-point scanned intensity-correlation measurements in the arms. In this work, we introduce a novel ghostlike imaging method that uses a Mach-Zehnder interferometer and is based on optical-field interference instead of intensity correlations. The method allows us to obtain sharp images of microscopic objects even in the presence of severe aberrations that completely destroy the intensity-based image. Furthermore, pure phase objects can be imaged with micrometer-scale resolution in the presence of strong aberrations, which has not been demonstrated previously with a correlation-based imaging technique. In the setup, we use a light-emitting diode source and an ordinary camera as the only light detector. The imaging approach that we put forward in this work may find significant applications in advanced optical microscopy, optical coherence tomography, and a variety of interferometric sensors and detectors.

Ghost Imaging Using Optical Correlations

AbstractGhost imaging uses optical correlations to enable an alternative and intriguing image acquisition technique: even though information from either one of the detectors used for the acquisition does not yield an image, an image can be obtained by harnessing the optical correlations. This Review describes a variety of both quantum and classical ghost imaging techniques, and seeks to point out where these techniques may have practical applications.

A novel semiconductor-based, fully incoherent amplified spontaneous emission light source for ghost imaging

Initially, ghost imaging (GI) was demonstrated with entangled light from parametric down conversion. Later, classical light sources were introduced with the development of thermal light GI concepts. State-of-the-art classical GI light sources rely either on complex combinations of coherent light with spatially randomizing optical elements or on incoherent lamps with monochromating optics, however suffering strong losses of efficiency and directionality. Here, a broad-area superluminescent diode is proposed as a new light source for classical ghost imaging. The coherence behavior of this spectrally broadband emitting opto-electronic light source is investigated in detail. An interferometric two-photon detection technique is exploited in order to resolve the ultra-short correlation timescales. We thereby quantify the coherence time, the photon statistics as well as the number of spatial modes unveiling a complete incoherent light behavior. With a one-dimensional proof-of-principle GI experiment, we introduce these compact emitters to the field which could be beneficial for high-speed GI systems as well as for long range GI sensing in future applications.

Photon-statistics-based classical ghost imaging with one single detector.

We demonstrate a novel ghost imaging (GI) scheme based on one single-photon-counting detector with subsequent photon statistics analysis. The key idea is that instead of measuring correlations between the object and reference beams such as in standard GI schemes, the light of the two beams is superimposed. The photon statistics analysis of this mixed light allows us to determine the photon number distribution as well as to calculate the central second-order correlation coefficient. The image information is obtained as a function of the spatial resolution of the reference beam. The performance of this photon-statistics-based GI system with one single detector (PS-GI) is investigated in terms of visibility and resolution. Finally, the knowledge of the complete photon statistics allows easy access to higher correlation coefficients such that we are able to perform here third- and fourth-order GI. The PS-GI concept can be seen as a complement to already existing GI technologies thus enabling a broader dissemination of GI as a superior metrology technique, paving the road for new applications in particular with advanced photon counting detectors.

Ultrabroadband ghost imaging exploiting optoelectronic amplified spontaneous emission and two-photon detection.

Ghost imaging (GI) is one of the recent fascinating and probably counterintuitive topics of quantum optics. Here, we present an alternative classical GI scheme using spectrally ultrabroadband amplified spontaneous emission from an optoelectronic quantum dot based superluminescent diode source. This light source exhibits highly incoherent properties regarding both first- and second-order correlations with a 70 nm-wide optical spectrum as well as thermal-like photon statistics. Exploiting a two-photon-absorption detection method, we demonstrate for the first time, to the best of our knowledge, a GI experiment handling the corresponding femtosecond correlation timescales. By introducing compact broadband light sources to GI, this work contributes toward practical application of GI.

Grayscale object authentication based on ghost imaging using binary signals

In recent years, either quantum or classical ghost imaging has attracted much attention in many fields. Here, we report grayscale object authentication based on ghost imaging using binary signals. It is found that binary signals can be applied at reference and object beam arms, which provides a promising alternative to explore the potential of ghost imaging for some applications. Reducing the data size with only two quantization levels is beneficial to the storage and transmission. One numerical example, i.e., grayscale object authentication, is given to illustrate the feasibility of the proposed method, and it is highly expected that more studies can further explore the ghost imaging system using binary signals for other applications.

Image quality in double- and triple-intensity ghost imaging with classical partially polarized light

Classical ghost imaging is a correlation-imaging technique in which the image of the object is found through intensity correlations of light. We analyze three different quality parameters, namely the visibility, the signal-to-noise ratio (SNR), and the contrast-to-noise ratio (CNR), to assess the performance of double- and triple-intensity correlation-imaging setups. The source is a random partially polarized beam of light obeying Gaussian statistics, and the image quality is evaluated as a function of the degree of polarization (DoP). We show that the visibility improves when the DoP and the order of imaging increase, while the SNR behaves oppositely. The CNR is for the most part independent of DoP and the imaging order. The results are important for the development of new imaging devices using partially polarized light.

Fractional Fourier transform in temporal ghost imaging with classical light

We investigate temporal, second-order classical ghost imaging with long, incoherent, scalar plane-wave pulses. We prove that in rather general conditions, the intensity correlation function at the output of the setup is given by the fractional Fourier transform of the temporal object. In special cases, the correlation function is shown to reduce to the ordinary Fourier transform and the temporal image of the object. Effects influencing the visibility and the resolution are considered. This work extends certain known results on spatial ghost imaging into the time domain and could find applications in temporal tomography of pulses.

A conceptual experiment on single-beam coincidence detection with pseudothermal light

Ghost imaging produced by pseudothermal light is commonly obtained by correlating the intensities of two separate beams, neither of which conveys information about the shape of the object to be imaged. The single-beam experiment discussed here, while not exploitable for the practical purpose of reconstructing the shape of a real mask, uses the same mathematical machinery as two-beam experiments; it also suggests that image retrieval by classical light ghost imaging is only a product of normal signal processing and does not involve any "ghost". In addition, the singlebeam setup allows simpler calibration procedures in systematic investigations of the efficiency of coincidence imaging.

Resolution of quantum and classical ghost imaging

The quantum ghost imaging phenomena, experimentally demonstrated a decade ago, exploited the apparent spooky action at a distance of entangled photon pairs and offered a novel approach toward imaging. Can ghost imaging effects be produced by ``classical'' light sources, such as separable systems of photon pairs or thermal light? If so, can these sources achieve the same accuracy achieved by entangled states? In order to answer these questions, we formulate the different physics behind entangled and separable systems in terms of a set of inequalities derived from the historical argument of Einstein, Podolsky, and Rosen. We show that the ghost images produced by separable sources are subject to the standard statistical limitations. However, entangled states offer the possibility of overcoming such limitations. Imaging can, therefore, achieve its fundamental limit through the high spatial resolution and nonlocal behavior of entangled systems.