Double-slit experiments
In the classic double-slit experiment (left) an interference pattern is formed on the screen (bottom left) when light passes through a pair of parallel slits in an opaque mask. If the light passes through a single slit, an interference pattern is not seen (right-hand screen). In the attosecond double-slit experiment (right), an ultrashort laser pulse is focussed into a gas of argon atoms, which are sometimes ionized by one of the peaks in the electric field (red line) of the laser: the resulting electron is then accelerated towards one of two detectors. Interference is observed by the detector on the left because we do not know if the electron was released from the atom by the first or second peak of the laser. Interference is not observed by the detector on the right because there was only one peak that could have released the electron.