Nonlinear optics in Epsilon-Near-Zero and time-oscillating media
Standard nonlinear optical processes occur in a regime in which the nonlinear material is signficantly thicker than the wavelength of the involved optical signals. However, there is also interest mainly inspired by fundamental physics, to study parametric processes in the regime in which the material is much shorter than the optical wavelengths. In this case, the medium may be considered to be oscillating uniformly in time and can provide a platform to study, for example, the spontaneous emission of photons from a periodically oscillating boundary a.k.a. the dynamical Casimir effect. We will first overview some of our recent work aimed at developing parametric processes in subwavelength films. Amongst a variety of failures, which we will only briefly mention, one class of materials has emerged as a very promising candidate for applications also beyond the original dynamical Casimir idea.
Very standard transparent conductive oxides such ITO or AZO exhibit a dielectric-to-metal transition in the near-infreared region (1300-1500 nm). At this transition the real part of the dielectric permittivity (epsilon) goes to zero with a relatively small imaginary part and as a result of which, the refractive index can also be very small (of order of 0.2). This low index leads to an enhancement of nonlinear effects, such as the Kerr nonlinear refractive index and four-wave-mixing that can be fully exploited thanks also to the very high damage intensity thresholds.
Recent studies are also starting to uncover the possibility to observe strong coupling between the plasmonic mode of a metallic nano-antenna (deposited on the ENZ film) and the ENZ-mode of a very thin (20-40 nm) ENZ film, thus promising further enhancement and avenues for interesting discoveries. We will then discuss other dynamical Casimir-like effects in periodically modulated photonic crystal fibres with first experimental results showing emission of non-classical states of light from a `dispersion-oscillating’ optical fibre.
Vortragender: Prof. Dr. Daniele Faccio, University of Glasgow
Kontakt: PD Dr. Maria Chekhova