These are the three pairs of rotational stages and glass used to control the arrival times of the laser pulse sequence for the 2D spectrometer. The stages are computer controlled, and can rotate with an accuracy of one-thousandth of a degree. By rotating the glass, the effective thickness increases, delaying the laser pulse with control on the attosecond time scale. A pair of glass plates are used for each beam, rotated at opposite angles to correct for the path deviation.
