Self-adjusted all-dielectric metasurfaces for deep ultraviolet femtosecond pulse generation.

The advantage of metasurfaces and nanostructures with a high nonlinear response is that they do not require phase matching, and the generated pulses are short in the time domain without additional pulse compression. However, the fabrication of large-scale planar structures by lithography-based methods is expensive, time consuming, and requires complicated preliminary simulations to obtain the most optimized geometry. Here, we propose a novel strategy for the self-assembled fabrication of large-scale resonant metasurfaces, where incident femtosecond laser pulses adjust the initial silicon films via specific surface deformation to be as resonant as possible for a given wavelength. The self-adjusting approach eliminates the necessity of multistep lithography and designing, because interference between the incident and the scattered parts of each laser pulse "imprints" resonant field distribution within the film. The self-adjusted metasurfaces demonstrate a high damage threshold (≈1012 W cm-2) and efficient frequency conversion from near-IR to deep UV. The conversion efficiency is up to 30-fold higher compared with nonresonant smooth Si films. The resulting metasurfaces allow for the generation of UV femtosecond laser pulses at a wavelength of 270 nm with a high peak and average power (≈105 W and ≈1.5 µW, respectively). The results pave the way to the creation of ultrathin nonlinear metadevices working at high laser intensities for efficient deep UV generation at the nanoscale.

Emulation of Fabry-Perot and Bragg resonators with temporal optical solitons.

The scattering of weak dispersive waves (DWs) on several equally spaced temporal solitons is studied. It is shown by systematic numerical simulations that the reflection of the DWs from the soliton trains strongly depends on the distance between the solitons. The dependence of the reflection and transmission coefficients on the inter-soliton distance and the frequency of the incident waves are studied in detail, revealing fascinating quasi-periodic behavior. The analogy between the observed nonlinear phenomena in the temporal domain and the usual Fabry-Perot and Bragg resonators is discussed.