Silicon-substrate-induced enhancement of infrared light absorption for all-optical magnetic switching

Enhancing the strength of optical absorption represents an important route toward improving the energy-efficiency of light-based technologies. Here, we experimentally and numerically explore how silicon substrates—long considered to be mere supporting structures for CMOS-compatible materials—can be exploited to improve optical absorption in the mid- to far-infrared spectral ranges, thus reducing the energy requirement for all-optical switching of magnetization. We show that infrared illumination of the metal through a 500 μm-thick silicon substrate actually deposits more energy in the metal film (by a factor of almost 3) compared to the conventional approach of illuminating the metal directly. Our results reveal that silicon substrates can actually play a crucial role in the efficient optical delivery of energy to functional materials and will find application in a wide range of experiments and technologies involving mid- and far-infrared light.