Fig. 5.
Detection schemes for measuring femtosecond and attosecond compressed electron packets. (Upper) Depicts how femtosecond electron packets can be measured by intersecting the packet at the image position/time. (A) Spatial profile of the donut mode temporal lens. (B) Gaussian profile of the measuring laser pulse. As the time delay, Δt, between the measuring Gaussian laser pulse and the electron packet is varied the average energy of the electron pulse changes. (Lower) depicts the scheme for measuring the duration of attosecond pulses. (C) The spatial profile of the temporal lens at t = 0 is shown (green). (D) The second standing wave that is used to measure the pulse duration of the attosecond electron packets at t = tf is displayed. The blue lines in C and D give the spatial distribution of the electron packets at t = 0 and t = tf, respectively. To measure the duration of the attosecond pulses, a second copropagating standing wave is made to coincide with the electron pulse at the focal position. Instead of using a temporal delay a phase shift, Δϕ, is introduced into one of the laser pulses that creates the probing standing wave. By varying this phase shift the nodes of the standing wave shift position. The average electron energy can thus be plotted versus this phase shift. As the electron pulses become shorter than the period of the standing wave the change in the average energy will increase.