Airy wave packets accelerating in space-time

Although diffractive spreading is an unavoidable feature of all wave phenomena, certain waveforms can attain propagation-invariance. A lesser-explored strategy for achieving optical selfsimilar propagation exploits the modification of the spatio-temporal field structure when observed in reference frames moving at relativistic speeds. For such an observer, it is predicted that the associated Lorentz boost can bring to a halt the axial dynamics of a wave packet of arbitrary profile. This phenomenon is particularly striking in the case of a self-accelerating beam -- such as an Airy beam -- whose peak normally undergoes a transverse displacement upon free-propagation. Here we synthesize an acceleration-free Airy wave packet that travels in a straight line by deforming its spatio-temporal spectrum to reproduce the impact of a Lorentz boost. The roles of the axial spatial coordinate and time are swapped, leading to `time-diffraction' manifested in self-acceleration observed in the propagating Airy wave-packet frame.Comment: 5 pages, 4 figure

Self-healing of space-time light sheets

Space-time wave packets are diffraction-free, dispersion-free pulsed beams whose propagation-invariance stems from correlations introduced into their spatio-temporal spectrum. We demonstrate here experimentally and computationally that space-time light sheets exhibit self-healing properties upon traversing obstacles in the form of opaque obstructions. The unscattered fraction of the wave packet retains the spatio-temporal correlations and thus propagation-invariance is maintained. The scattered component does not satisfy the requisite correlation and thus undergoes diffractive spreading. These results indicate the robustness of ST wave packets and their potential utility for deep illumination and imaging in scattering media such as biological tissues.Comment: 5 pages, 3 figure