Spatiotemporal Couplings in Ultrashort Laser Pulses: Fundamentals, High-Field Interactions, and MEMS-Enabled Control for Micromachining

Spatiotemporal couplings are defined by non-separable spatial and temporal or spectral dependences of the optical field. They must be distinguished from the kinematic conversion between pulse duration and longitudinal spatial extent, s = cτ, which applies to a rigidly translating profile in vacuum under specified observation conditions. This review examines theoretical and experimental frameworks developed to describe such regimes, where diffraction–dispersion analogies coexist with angular dispersion, pulse-front tilt, space-dependent spectra, and structured spatiotemporal wave packets and discusses their influence on peak intensity, nonlinear absorption, energy deposition, ablation, heat-affected zones, processing resolution, surface quality, and reproducibility, while highlighting the emerging role of MEMSs and micromachine-based optical systems in enabling precise control of these processes for advanced laser micromachining. Particular attention is devoted to the fundamental concepts of spatiotemporal analogies, spatiotemporal couplings in ultrashort pulses, and the corresponding spatiotemporal effects relevant to petawatt laser systems. The influence of these effects in ultrashort and ultra-intense laser systems is discussed, where spatiotemporal distortions impact focal intensity and pulse duration. We highlight how spatiotemporal structuring of ultrashort and ultra-intense laser pulses, combined with tailored micro- and nanostructured targets, enables control of field localization, energy deposition, and laser–matter coupling. By proceeding beyond a direct space–time equivalence, spatiotemporal analogies provide essential insight for both fundamental understanding and practical optimization of ultrashort and ultra-intense laser–target interactions.