Temperature-dependent optical constants of vanadium dioxide thin films deposited on polar dielectrics

Coating polar dielectrics with thin film vanadium dioxide (VO 2 ) enables one to exploit the temperaturedependent phase transition within VO 2 to actively tune and modulate surface phonon polaritons at midinfrared. However, controlling the behavior of such systems requires intimate knowledge of the temperaturedependent optical constants of VO 2 , which depend greatly on the growth conditions and substrate material. Here, we accurately determine the complex optical constants of VO 2 on polar dielectrics across the insulator-tometal phase transition (IMT) using only normal incident reflectance spectra by analyzing the reflectance with Kramers-Kronig relations and thin film Fresnel equations. This non-ellipsometry technique offers an advantage in determining the refractive index using a standard infrared spectrometer.