Novel optical sensing approach using spectral correlation

In contrast with direct measurement methods, correlation imaging measures the correlation function between the intensity emitted by a light source and the total (integrated) intensity transmitted (or reflected) by an ob- ject, such that the image can be constructed without the object to be actually seen. The essential nature of such “ghost imaging” lies in the mutual spatial correlation of the two beams, and the image can be simply obtained by summing all of the probing patterns, each weighted by the integrated signal from the detector. Here, we demonstrate for the first time ghost imaging in the spectral domain using a light source with shot- to-shot random spectral fluctuations. The advantage of the correlation approach is that it only detects the to- tal integrated signal after the object and thus can be in principle very sensitive even in low light conditions or in spectral regions where no fast detector exists. It is also inherently insensitive to any perturbation occurring between the object and the detector.