Abstract
We analyse possibilities to quantitatively evaluate the surface second-order optical nonlinearity in noncentrosymmetric materials based on polarization-resolved analysis of far-field radiation patterns of second-harmonic generation. We analytically demonstrate that for plane-wave illumination the contribution to the second-harmonic signal from the surface of a nonlinear medium exhibits different polarization properties and angular dependencies compared to the contribution from the bulk. In view of this, we optimize the illumination geometry in order to enable the most efficient separation and comparison of both nonlinearities. Furthermore, we consider the illumination of an AlGaAs slab by a tightly-focused linearly-polarized Gaussian beam as an alternative measurement geometry. It is found that the reliable separation of the surface nonlinearity contribution as well as a wide range of detectable values can be achieved with this geometry as well.
Highlights
We analyse possibilities to quantitatively evaluate the surface second-order optical nonlinearity in noncentrosymmetric materials based on polarization-resolved analysis of far-field radiation patterns of second-harmonic generation
In ref. 20 it was found that resonantly enhanced Second-harmonic generation (SHG) from GaAs dielectric metasurfaces cannot be adequately described when assuming only bulk nonlinearity, it was concluded that the surface nonlinearity gives a noticeable contribution
We have shown here that due to different symmetry properties of the bulk crystal and the interface, the surface optical nonlinearity should exhibit specific signatures in the polarization-resolved far-field pattern allowing to separate it from the bulk nonlinear response
Summary
We are considering an unstructured interface between air and a semi-infinite nonlinear medium. We plot the δ-dependence of the total SHG intensity for a FW incidence angle φ = 60° and p-polarization with α = 0° in Fig. 4(a) for different ratios η of bulk and surface nonlinearities. Instead of performing an angular scan of the angle δ as for plane-wave illumination, using a TFGB should allow performing the whole quantitative comparison of the nonlinear sources by polarization-resolved analysis of a single measured SHG far-field radiation pattern Both bulk and surface SHG excited by tightly focused laser beams have been earlier studied theoretically and experimentally in different media, including isolated centrosymmetric nanospheres[40,41], metal nano-objects[42], glass slides[43,44] and silicon nanowires[45].
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