Image Quality Of Thermal High-order Correlated Imaging

The correlated imaging is a new imaging technique which was established in1980s. The original correlated imaging experiment was performed with two-photonentangled light produced through parametric down-conversion. At the beginning,there was an opinion that entanglement is a prerequisite for achieving distributedquantum imaging. However, with the development of the theory and the experimenttechnique, the correlated imaging can be performed with thermal light too.Considering the difficulty in achieving of quantum optical sources, correlatedimaging with thermal source has been attracting increasing attention in many fields.In thermal correlated imaging, the second-order correlation function contains a noisebackground term, which leads to lower visibility compared with correlated imagingwith quantum optical sources. In order to improve the visibility of thermal correlatedimaging, especially for an image of the complex object, studies on both the theoryand the experiment shows that the visibility rapidly increases when increasing theorder N of the correlation function. Therefore, the high-order thermal correlatedimaging becomes a hot topic in the field of thermal correlated imaging.In this paper, the aim was focused on the quality of the high-order thermalcorrelated imaging. Both the visibility and the signal-to-noise were studied for thethird-order correlated imaging. Based on the previous study, the three detectors werefirstly used to measure the third-order intensity correlation in three paths.Accordingly, the third-order HBT experiment and the third-order correlated imagingexperiment were performed with pseudothermal radiation. The second-order and thethird-order correlated imaging, the curve of visibility and the curve of thesignal-to-noise were shown in the experiment result. The comparison between thesecond-order imaging and the third-order imaging shows that the visibility of thethird-order correlated imaging was higher than the second-order correlated imaging.It demonstrates that the visibility increases when increasing the order N of thecorrelation function. Furthermore, it confirms the significant of the study on high-order correlated imaging. In addition, the signal-to-noise decreases whenincreasing the order N of the correlation function. In order to enhance thesignal-to-noise, an improved correlation function was used to eliminate the noisebackground encountered in the third-order correlated imaging, which can improve theimage quality.