Fig. 4.

2D schematic of tilted laser pulse concept for copropagating standing wave used for attosecond electron compression (thick temporal lens). When θ₁ = θ₂ = 0, then v₀ = c/3 for ω and 2ω beams (14). With frequencies of ω and 2ω the velocity of the copropagating standing wave can be tuned by tilting the 2 laser pulses angles θ₁ and θ₂. When the 2 angles are chosen according to θ₂ = arcsin(2sinθ₁), the wells in the standing wave are perpendicular to the electron propagation.