Spatio-temporal photonic metalattice

When coherent light interacts with an ordered lattice with periodicity comparable to its wavelength, a diffraction pattern emerges. The same principle applies in crystallography, where X-rays are employed to reveal atomic structures. By asking 'when' the diffractive object exists, rather than 'where', we implicitly introduce time as a design parameter, thus enabling the creation of spatio-temporal metalattices. The temporal modulation of optical properties complements the spatial one, enabling functionalities such as dynamic reconfigurability, nonreciprocal behavior, coherent amplification, and tailored spectral response. However, for these effects to be relevant an extreme temporal gradient of the refractive index is necessary. In the present work, we realize a two-dimensional spatio-temporal metalattice by integrating a physically patterned spatial modulation with an orthogonal temporal lattice induced by interfering ultrafast pulses, using highly nonlinear transparent conducting films operated within their low-index window. While the optical pumps experience a uniform medium, the spatio-temporal lattice can be probed by either an internally generated third harmonic signal, or an externally supplied probe wave. The transient lattice shows comparable diffraction efficiency to the equivalent physical structure and is also dynamically reconfigurable via a broad range of parameters, including the pulses delay, incidence angle, and wavelength. System flexibility is also demonstrated through phase-mask wavefront modulation, highlighting exceptional versatility for ultrafast transient lithography and photon manipulation in both momentum and frequency. This approach shifts device design from fixed fabrication constraints to radiation engineering, opening new pathways towards ultrafast reconfigurable photonics.