Ultrafast Nonlinear Optics in the Mid-Infrared

Abstract

The mid-infrared spectral range is unique in many ways. Within this region, electromagnetic radiation can resonate with the most intense signature molecular bands, thus drastically enhancing the coupling between the field and molecular motions. Electrons driven by intense ultrashort mid-IR field waveforms acquire unusually high ponderomotive energies within a fraction of the field cycle, giving rise to new regimes of high-field nonlinear optics. The λ2 scaling of phase-space mode volume with radiation wavelength λ translates into the λ2 dependence of the self-focusing threshold, allowing much higher peak powers to be transmitted in a single laser filament in the mid-IR range without losing beam continuity and spatial coherence. Recent breakthroughs in the generation of high-intensity ultrashort pulses in the mid-IR help understand complex interactions of high-intensity ultrashort mid-IR pulses with matter, offer new approaches for coherent and incoherent x-ray generation, enable mid-IR laser filamentation in the atmosphere, facilitate lasing in filaments, give rise to unique regimes of laser-matter interactions, and reveal unexpected properties of materials in the mid-IR range.