Engineering space-time wavepackets into non-paraxial regime by dispersion magnifier

We theoretically propose a spatiotemporal pulse shaping method to generate space-time wavepackets beyond the paraxial regime using conventional optical elements. Space-time wavepackets are a distinctive class of structured optical pulses with non-dispersive and non-diffractive characteristics in free space. The formation of a space-time wavepacket has been limited in the paraxial regime due to the requirement of angular spectral dispersion engineering. We show that a dispersion magnifier, consisting of four positive lenses, can stretch or shrink the magnitude of transverse wavevectors of space-time wavepacket in Fourier space by geometrical magnification. The dispersion magnifier can result versatile control of the group velocity, maximum numerical aperture, beam diameter, and propagation distance, depending on the magnification factor of the dispersion magnifier and the initial group velocity of the space-time wavepacket. Our result suggests a promising application for the demonstration of long-distance propagation of optical pulses with wavelength-scale cross-section.