Enhanced Polarization Response of Epsilon-Near-Zero Materials at Near-Infrared Wavelengths

Epsilon near zero (ENZ) materials are known to exhibit a strong plasmonic and optoelectronic response around their ENZ wavelengths, making them desirable for several photonics applications. Of particular interest are transparent conducting oxides such as CdO (Cadmium oxide) and ITO (Indium tin oxide) thin films that feature improved transmittance and low resistivity at ENZ wavelengths. In this work, we focus on using pump-probe laser spectroscopy to interrogate the magneto-optic response of Gd-doped and In-doped CdO films at near-IR ENZ wavelengths (0.760 – 2.2 μm). We use both laser reflectance (Kerr effect) and transmittance (Faraday effect) measurements to determine the wavelength-dependent polarization response of CdO:Gd and CdO:In films, which we then utilize to calculate the Verdet constant. Our magneto-optic experiments, when performed in static-mode, reveal that CdO:Gd films feature extremely high Verdet constants at ENZ wavelengths. Through time-resolved experiments, we shed light on the quasi-particle interactions that enable energy relaxation mechanisms in these systems.