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 object, such that the image can be reconstructed without the object to be actually seen. The essential nature of such “ghost imaging”  lies in the mutual correlation of the two non-interacting beams, and the image is obtained by summing over the different probing patterns weighted by the integrated signal from the detector . Here, we demonstrate for the first time broadband ghost imaging in the spectral domain using a supercontinuum source . We demonstrate the approach by using a gas cell filled with pure methane as the object in the test arm and reconstruct its absorption spectrum. The advantage of the correlation approach is that it detects the total integrated signal after the object and is thus 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.
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