Correlated two-photon imaging with true thermal light

Abstract

We report the first experimental demonstration of two-photon correlated imaging with true thermal light from a hollow cathode lamp. The coherence time of the source is much shorter than that of previous experiments using random scattered light from a laser. A two-pinhole mask was used as object, and the corresponding thin lens equation was well satisfied. Since thermal light sources are easier to obtain and measure than entangled light it is conceivable that they may be used in special imaging applications.Although imaging is an old and well-studied topic and is of great importance in classical optics, it is now attracting new interest in quantum optics due to recent experiments on two-photon correlated imaging. The first such experiment was based on quantum entangled photon pairs from spontaneous parametric down conversion in a nonlinear crystal, and gave rise to the name "ghost" imaging, so called because an object in one optical beam could produce an image in the coincident counts with a detector placed in another beam [1]. This experiment led to other interesting theoretical and experimental studies and, furthermore, a debate on the question whether entanglement is a prerequisite for ghost imaging [2]. The possibility to perform correlated imaging with thermal light was first predicted by Gatti et al [4]. The first experiment with a classical light source that demonstrated "two photon" coincidence imaging was performed by Bennink et al. using a coherent laser beam split along two paths with detectors that measured finite laser pulses [3].The difference between quantum and classical coincidence imaging and the extent to which a classical light source can mimic a quantum one have been widely discussed by the groups of Shih [5,6], Boyd [7], Lugiato [4,8,9], Zhu [10, 11] and Wang [12]. Experimentally, Shih and collaborators first achieved ghost imaging with a pseudo-thermal light source, and introduced the concepts of "two-photon coherence" and "twophoton incoherence" imaging [13]. Gatti et al. obtained high resolution ghost imaging with thermal-like speckle light. However, in all these experiments the primary light source was a He-Ne laser, and the pseudo-thermal beam was obtained by passage through a rotating ground glass plate [14].Different from these experiments, we report the demonstration of a two-photon correlated imaging experiment using a true thermal light source.We employed a commercial rubidium hollow-cathode lamp [16] manufactured by the General Research Institute for Nonferrous Metals (China), which is the type commonly used in atomic absorption spectroscopy because of its sharp spectral linewidth. The lamp was powered by a direct current of 20mA in our experiments, and the resonance wavelength was 780nm. However, the actual linewidth of hollow-cathode lamps depends on the pressure, filament structure etc and varies from model to model. In our model the inner diameter of the cathode was 3mm. To estimate the coherence time of our lamp we first carried out a Hanbury Brown-Twiss (HBT) type experiment...

Super-thermal light for imaging applications

“…This result re ects the relation between the value of the autocorrelation function and the number of modes, already shown in Eqs. (7) and (9). In more detail, we notice that since the CCD camera is a macroscopic detector, the two expressions of g ( ) simplify as the last term on the right side can be neglected.…”

“…The image of the object is recovered by correlating the intensities measured by the bucket detector with the intensities measured by each pixel of the spatial-resolving detector [3]. The geometry of light propagation required to reconstruct the image depends on the speci c kind of correlated beams in use: ghost imaging protocols with twin beams require the use of lenses [4][5][6][7], while those performed with thermal light can be lensless [8,9].…”

High-visibility ghost imaging from artificially generated non-Gaussian intensity fluctuations

“…The first experiment was demonstrated with entangled light obtained from spontaneous parametric down conversion, 1 and the phenomenon was once considered as a characteristic of the nonlocality of entanglement, 2 hence the name "ghost" imaging was coined. Later, it was found that thermal light can also be used to realize GI, [3][4][5][6][7][8][9][10][11] which has many advantages as the source is readily available and has higher intensity so less data acquisition time is needed. However, a fundamental disadvantage is that there is always a large background, which restricts the maximum visibility to 1/3, compared to 1 for entangled light.…”

Odd-order aberration cancellation in correlated-photon imaging

“…The results were similar to those with the entangled source, but with half the visibility. It has since been shown that spatial correlations present in radiation produced using thermal and speckle sources may also lead to ghost imaging ( [4][5][6][7][8][9]). …”