Fig. 2.
Ray diagrams for spatial and temporal lenses. (Upper) Depicts 3 primary rays for an optical thin spatial lens. The object is located at yo, and the spatial lens has a focal length, f. A real image of the object is created at the image plane, position yi. (Lower) Ray diagram for a temporal thin lens. The diagram is drawn in a frame moving with the average speed v0 of the electron packet. The slopes of the different rays in the temporal diagram correspond to different initial velocities that are present in the electron packet. As shown in the diagram a temporal image of the original electron packet is created at the image time ti. The initial packet (object) is created at a time to with Δto = Δxo/v0, where the spatial extend of the pulse is directly related to the temporal duration of the object. The lens is pulsed on at t = 0 and the temporal focal length of the lens is tf. The lens represents the ponderomotive potential and in this case is on for the very short time τ.