Bandwidths limitations of giant optical field enhancements in dielectric multi-layers

Dielectric multilayers, when properly optimized, have been shown to sustain giant optical field enhancement directly linked to the imaginary index of the materials. Such giant optical field is of great interests to increase tremendously the sensitivity of optoelectronic systems. Unfortunately, this ultra-sensitive system is also highly depending on the illumination conditions. We discuss here the effect of the angular divergence and the spectral bandwidth of the incident laser beam on the absorption and field enhancement. In this study, we clearly show that giant optical field enhancements, up to several decades, may be achievable when the incident conditions are down few μrad and pm in term of angular and spectral bandwidths respectively.