Ultrafast nonlinear pulse propagation dynamics in metal-dielectric periodic photonic architectures

TL;DR

This paper investigates ultrafast nonlinear pulse propagation in metal-dielectric periodic structures, revealing enhanced nonlinear responses and potential for advanced ultrafast photonic devices through experimental and modeling approaches.

Contribution

It provides a detailed experimental and theoretical analysis of ultrafast nonlinear optical responses in 1D metal-dielectric structures, highlighting their enhanced nonlinearities and applications.

Findings

Enhanced nonlinear optical absorption due to free-carrier and excited-state processes

Spectral nonlinearities linked to dielectric function modifications

Ultrafast electron-electron and electron-phonon interactions observed

Abstract

One-dimensional (1D) metal-dielectric (MD) periodic structures take advantage of large refractive index contrast between metal and dielectrics to invoke extremely high nonlinear ultrafast responses of metal. These structures are also special due to their extremely high laser damage threshold. The Bragg like 1D MD structure (Ag/SiO2)4 enables strong optical field confinement with much enhanced nonlinear features as compared to simple metal or single (Ag/SiO2)1 structure. In the present work, the ultrafast nonlinear optical responses of the above structures are investigated via femtosecond broadband optical pump-probe technique. The enhanced nonlinear optical absorption is of reverse saturation of absorption (RSA) nature, resulted due to free-carrier absorption (FCA) and excited-state absorption (ESA) processes. The spectral nonlinearities are closely related to the pump-induced modification of the metal's dielectric functions, which are qualitatively visualized by transfer matrix and two-temperature models. The ultrafast temporal evolution of nonlinear absorption clearly demonstrated enhanced optical nonlinearity, disentangled by the electron-electron and electron-phonon dynamic interactions at picosecond time scales. A phenomenological pulse propagation model is employed that incorporates the experimentally obtained nonlinear absorption coefficients and different nonlinear effects exhibited by the system. Nonlinearity plays a crucial role in controlling the ultrafast pulse propagation and could open a new window for many nonlinear device applications. The findings of these new optical materials could possibly pave the way for promising applications in ultrafast photonics.