Directionally selective optical limiting of femtosecond pulses in simple transparent two-layer systems

Directionally selective nonlinear transmission behavior has been observed for simple glass-based two-layer systems in Z-scan experiments employing femtosecond pulses at a wavelength of λ=800 nm. Glass sheets of 1 mm thickness with a very thin surface layer (~2 μm) containing spherical Ag nanoparticles have been studied. In these samples, irradiating from the substrate side causes a strong transmission decrease via self-focusing of the beam and subsequent two-photon absorption in the thin layer, whereas the reverse direction may pass the sample without loss. This anisotropic optical limiting is discussed in terms of a numerical model in the limit of thin samples with respect to the Rayleigh range of the laser beam.