Figure 5

Group-velocity-tunable propagation-invariant optical wave-packet generated by the conical superposition is subset of space–time wave-packet. Spatiotemporal spectrum (colored thick line on light-cone) of propagation-invariant optical wave-packet generated by the conical superposition is a part of that of space–time wave-packet, excluding k_⊥ = 0. When (a,b) spectral range of pulse is enhanced, or spectral plane is (c,d) shifted towards positive direction of k_z-axis, or spectral plane is dramatically rotated (e) counterclockwise or (f) clockwise, spatiotemporal spectrum of propagation-invariant optical wave-packet is changed from two separate curves about k_⊥ = 0 plane into a single continuous one, and propagation-invariant optical wave-packet becomes space–time wave-packet. ω_l, ω₀, and ω_h are the lowest, center and highest angular frequencies of pulse. Figure generated by Microsoft® Visio® 2013⁵⁰.