region, also known as the ENZ region. Ideally, when e → 0 the wavelength of light within the ENZ medium approaches infinity, its group velocity tends to zero, and the normal component of the transverse magnetic (TM) polarized light experiences a large enhancement. [1][2][3] As a result of these unconventional optical properties, interesting optical phenomena such as wave tunneling, [4] directional emission, [5] frequency conversion, [6][7][8] intensitydependent refraction, [9][10][11][12][13][14][15] and frequency translation due to time-varying refractive index [16] have been realized in ENZ materials. A well-known class of ENZ media includes transparent conducting oxides (TCOs) such as indium-tin oxide (ITO), [9] aluminum-zinc oxide (AZO), [10] and indium-cadmium oxide (ICO). [15] These are n-type semiconductors with a freeelectron density on the order of − 10 cm 20 3

We report the linear and nonlinear optical properties of Zirconium-doped Indium Oxide film in the near-zero permittivity spectral region. We observe a relatively broadband nonlinear response, which could be due to a gradient permittivity.