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.
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.
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.
Ghost metrology is a measurement modality exploiting correlations of photons. At ICTON 2017 [1], we had demonstrated ghost imaging by using a novel, extremely compact superluminescent diode source based on Amplified Spontaneous Emission and exhibiting photon bunching. Here, we now demonstrate that amplified spontaneous emission light emitted both by a spectrally broad-band semiconductor-based superluminescent diode and an erbium-doped fibre amplifier (EDFA) exhibit spectral photon correlations in the spirit of the Hanbury-Brown & Twiss (HBT) experiment, however now in the spectral domain. We then apply these spectral photon correlations within two proof-of-principal ghost spectroscopy experiments, one at an absorption band of trichloromethane (chloroform) at 1214 nm and another one at 1533nm at acetylene (C2H2) reproducing the characteristic absorption features. This ghost spectroscopy work fills the gap of a hitherto missing analogy between the spatial and the spectral domain in classical ghost modalities. Finally, by exploiting polarization correlations of light from an EDFA we succeed in reconstructing a hidden, camouflaged polarization in a ghost polarimetry experiment in close analogy to ghost imaging and ghost spectroscopy. Via these successfully demonstrated results, we are contributing towards a broader dissemination of correlated photon ghost modalities, hence paving the way towards more applications which exploit their favourable advantages.
Ghost imaging (GI) has been under development for several years and is now achievable in both single- and multiphoton regimes with both quantum and classical light. Here, we address the experimental challenge of using sunlight as a pump beam to excite spontaneous parametric down-conversion and generate photon pairs. Remarkably, our investigations reveal that photon pairs excited from sunlight exhibit strong positional correlation, enabling their application in GI with an efficiency comparable to that achieved using a laser with similar pump power. This finding demonstrates the potential of employing an incoherent beam as the pump source in GI systems. Our research holds substantial significance as it expands the range of viable illumination sources—including scattered light and nontraditional artificial incoherent light—for imaging applications. A key potential use is in space-based quantum information systems, where this approach enables operation independent of laser sources.
Ghost modalities are by no means ``spooky actions'', but are metrology schemes exploiting intensity correlations of light, based on the fundamentals of quantum optics. The authors demonstrate ghost spectroscopy based on classical photon correlations in the wavelength domain of broad-band light emitted by an ultraminiaturized superluminescent semiconductor diode. Comprehensive proof of principle is provided by a real-world experiment on chloroform at 1214 nm. This demonstrated analogy between ghost imaging and ghost spectroscopy is expected to further fertilize the field, to promote a deeper understanding, and to lead even to other protocols in ghost metrology.
Ghost imaging is a novel non-conventional technique allowing to generate high resolution images by correlating the intensity of two light beams, neither of which independently contains sufficient information about the spatial distribution and shape of the object. The first demonstration of ghost imaging used light in double photon state, obtained from spontaneous parametric down-conversion. Owing to the entanglement of the source photons, the proposed theory required quantum descriptions for both the optical source and its photo-detection statistics1. However, subsequent experimental and theoretical considerations2,3 demonstrated that ghost imaging can be performed also with thermalized light, utilizing either CCD detector arrays or photon-counting detectors, thus admitting to a semi-classical description, employing classical fields and shot-noise limited detectors. This has generated increasing interest4-6 in establishing a unifying theory that characterizes the fundamental physics of ghost imaging and defines the boundary between classical and quantum domains. In this view, we exploited recent progress obtained through the application of Fourier Transform Techniques to demonstrate ghost imaging in the frequency domain, in order to measure a continuous spectrum by using a highly brilliant and coherent monochromatic source. In particular, we demonstrate the application of this ghost imaging technique to broadband spectroscopic measurements by means of interaction free photon detection. The experimental apparatus and the collected data are described in a dedicated work7. In this paper, we consider the theoretical aspects underlying the proposed Spectroscopic technique. In particular, two alternative theoretical models are presented. In one case, a statistical approach (semi-classical) is applied, where the states of the sampling beam are considered, whereas in the other case a pure quantum treatment is carried on, by describing the interaction of vacuum states generated by photon conversion processes. Both theoretical models, though carried on by means of a complementary formalism, lead to equivalent results and offer a physical interpretation of the collected experimental data. The application of these results offer novel perspectives for remote sensing in low light conditions, or in spectral regions where sensitive detectors are lacking.
Developments in quantum technologies lead to new applications that require radiation sources with specific photon statistics. A widely used Poissonian statistics are easily produced by lasers; however, some applications require super- or sub-Poissonian statistics. Statistical properties of a light source are characterized by the second-order coherence function g^(2)(0). This function distinguishes stimulated radiation of lasers with g^(2)(0)=1 from light of other sources. For example, g^(2)(0)=2 for black-body radiation, and g^(2)(0)=0 for single-photon emission. One of the applications requiring super-Poissonian statistics (g^(2)(0)>1) is ghost imaging with thermal light. Ghost imaging also requires light with a narrow linewidth and high intensity. Currently, rather expensive and inefficient light sources are used for this purpose. In the last year, a superluminescent diode based on amplified spontaneous emission (ASE) has been considered as a new light source for ghost imaging. Even though ASE has been widely studied, its photon statistics has not been settled - there are neither reliable theoretical estimates of the second-order coherence function nor unambiguous experimental data. Our computer simulation clearly establishes that coherence properties of light produced by ASE are similar to that of a thermal source with g^(2)(0)=2 independent of pump power. This result manifests the fundamental difference between ASE and laser radiation.