Thermal ghost imaging with averaged speckle patterns

We present theoretical and experimental results showing that a thermal ghost imaging system can produce images of high quality even when it uses detectors so slow that they respond only to intensity-averaged (that is, ``blurred'') speckle patterns, as long as the collected signal variation is predominantly caused by the random fluctuation of the incident speckle field rather than other noise sources. In our experimental study, we show that the quality of the ghost image is not degraded when as many as 25 speckle patterns are averaged together for each measurement. This surprising result comes from the fact that the averaging of speckle patterns leads to a decrease in the contrast but not in the kurtosis, and the image quality of a ghost imaging system is dependent on the kurtosis rather than the contrast ratio of the illuminating field. These results suggest that a broad class of imaging systems based on the use of speckle techniques can be implemented even using detectors that respond slowly on the time scale of the fluctuating speckle pattern.