1. A method for probing an integrated circuit, comprising: collecting light emitted from a selected area of an integrated circuit; passing the light through a diffracting element to obtain diffraction spectrum; projecting the diffraction spectrum on a photosensor to obtain an image of the diffraction spectrum; displaying the image of the diffraction spectrum on a monitor; and, classifying a faulty device in the integrated circuit according to a shape of the image of the diffraction spectrum displayed on the monitor.