Since the quality of underwater classical optical imaging is constrained by the absorptive and scattering nature for underwater environment, it is a challenging task to obtain long distance imaging. Ghost imaging is a second-order correlation imaging method using co-incidence measurement, which has the advantages of disturbance-free and wider angle of view (AOV), which can effectively improve the imaging result. We have investigated the computational ghost imaging under the underwater conditions for different turbidities and from different angles. The reconstruction obtained by computational ghost imaging can be rather desirable, in the scenarios that the classical optical imaging method completely fails. Moreover, the underwater computational ghost imaging can bear a wide range of AOV, where the obtained imaging results can be satisfiable in regardless of the detector’s locations. This result brings a better alternative for underwater optical imaging.

In a near-field three-photon correlation measurement, we observed the third-order temporal and spatial correlation functions of chaotic thermal light in the single-photon counting regime. In the study, we found that the probability of jointly detecting three randomly radiated photons from a chaotic thermal source by three individual detectors is $6$ times greater if the photodetection events fall in the coherence time and coherence area of the radiation field than if they do not. From the viewpoint of quantum mechanics, the observed phenomenon is the result of three-photon interference. By making use of this property, we measured the three-photon thermal light lensless ghost image of a double spot and achieved higher visibility compared with the two-photon thermal light ghost image. DOI: http://dx.doi.org/10.1103/PhysRevA.81.043831 © 2010 The American Physical Society

This paper presents a unified theory for the $N\text{th}$-order $(N⩾1)$ coherence of thermal light. We wish to show that the $N\text{th}$-order coherence or correlation of thermal light is the result of $N$-photon interference, which involves the superposition of $N$-photon probability amplitudes, corresponding to different yet indistinguishable ways of triggering a $N$-photon joint detection event. The near-field third-order spatial coherence of thermal light is calculated and its use suggested for verifying the $N$-photon interference theory.

A simple superbunching pseudothermal light source is introduced based on common instruments such as laser, lenses, pinholes, and ground glasses. $g^{\left(2\right)}\left(0\right)=3.66\pm 0.02$ is observed in the suggested scheme by employing two rotating ground glasses. Quantum and classical theories are employed to interpret the observed superbunching effect. It is predicted that $g^{\left(2\right)}\left(0\right)$ can reach $2^N$ if $N$ rotating ground glasses were employed. These results are helpful to understand the physics of superbunching. The proposed superbunching pseudothermal light may serve as a type of light to study the second- and higher-order coherence of light and have potential application in improving the visibility of thermal light ghost imaging.

The spatial second-order interference of two independent pseudothermal light beams in a Hong-Ou-Mandel interferometer is studied experimentally and theoretically. The similar cosine modulation in the second-order coherence function as the one with entangled-photon pairs in a Hong-Ou-Mandel interferometer is observed. Two-photon interference based on Feynman’s path integral theory is employed to interpret the results. The experimental results and theoretical simulations agree with each other very well.

The second-order spatial subwavelength interference pattern is observed in a modified Michelson interferometer with single-mode continuous-wave laser beams. By analyzing our subwavelength interference experiment based on Feynman's path integral theory, a unified interpretation for all the second-order subwavelength interference is suggested.