Illuminating nonlinearities in epsilon-near-zero materials

Since the invention of the laser, nonlinear optical phenomena have been a cornerstone of photonics research empowering advances in both continuous and pulsed lasers, molecular spectroscopy, and sub-diffraction imaging others. Although many nonlinear media have been explored through the years, ever more compact and efficient platforms remain a key driver in the field. Recently epsilon-near-zero (ENZ) materials, media with a spectral range where|Re{e}| < 1, have emerged as a compact and versatile approach to enhance various nonlinear processes such as refractive index tuning, harmonic generation, and phase conjugation. In this talk, we discuss the unique underlying conditions that make ENZ materials a promising nonlinear platform and employ a framework of carrier kinetics to describe the nonlinear effects in Drude-based ENZ materials such as the transparent conducting oxides (TCOs). Through this approach, we focus on the large and ultrafast reflection and transmission modulation in TCOs enabled by the intensity-dependent refractive index, highlighting general trends as well as optimal material and excitation conditions. In particular, the role of absorption and non-parabolicity of the energy bands are discussed, culminating in a general figure of merit for comparing the performance of new potential ENZ materials. Finally, we describe recent advances utilizing the ultrafast refractive index tuning to generate an adiabatic frequency shift of a probe beam’s spectrum.