Nonlinear Čerenkov radiation from a single ferroelectric domain wall

Nonlinear optical Cerenkov emission represents the type of noncollinear parametric process where the direction of the generated wave is defined by the longitudinal phase matching condition [1]. In the simplest case of Čerenkov second harmonic generation (ČSHG), the radiation of the doubled frequency is observed at the angle defined as cosθ= 2k₁/k₂cosa, where k₁ and k₂ denote the wave vectors of the fundamental and the second harmonic (SH) waves, respectively, and a is the incident angle of the fundamental wave. Recently the ČSHG has attracted lots of attention because of the efficient noncollinear SHG eliminating the necessity of filtering out the incident wave in all-optical signal processing. Moreover, it also enables the spatial control of the generated wave front, e.g. forming the radially polarized Bessel beam.