Spatiotemporal refraction of light in an epsilon-near-zero indium tin oxide layer: frequency shifting effects arising from interfaces

When light travels through a medium in which the refractive index is rapidly changing with time, the light will undergo a shift in its frequency. Significant frequency shifting effects have recently been reported for transparent conductive oxides. These observations have been interpreted as emerging from temporal changes to the propagation phase in a bulk medium resulting from temporal variations in the refractive index. It is an effect referred to as temporal refraction. Here, we show that the frequency shift in an epsilon-near-zero layer made of indium tin oxide originates not only from this bulk response but includes a significant effect resulting from temporal changes to the spatial boundary conditions. This boundary effect can lead to a dominant, opposing shift to the bulk effect for certain angles. Hence, this process gives rise to a frequency shift that can be tailored through the angle, decoupling the amplitude and phase modulation. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

Automated summary

When light travels through a medium with changing refractive index over time, it can lead to a frequency shift. Recent studies have shown significant frequency shifting effects in transparent conductive oxides, likely due to temporal changes in the refractive index. Experimental results indicate that the frequency shift in certain materials originates not only from bulk response, but also from temporal changes in spatial boundary conditions.