Spatially resolved light field analysis of the second-harmonic signal of χ(2)-materials in the tight focusing regime

Abstract

In this work, the second-harmonic (SH) signal generated by nonlinear optical crystals is studied in the tightly focused regime. The experimental approach is based on an adapted focal imaging technique, which allows the mapping of the SH intensity distribution in the back focal plane via a traversable pinhole in the confocal operation mode. On the theoretical side, a vectorial treatment of the involved optical fields enables the description and interpretation of the occurring interactions by taking into account the applied experimental parameters. The theoretical results are exemplarily validated by comparison to the acquired experimental data gained by the examination of LiNbO3 and KTiOPO4. It is shown how the phase and amplitude of vector components of the incoming electromagnetic field in the focus as well as the local optical properties of the nonlinear optical crystals determine the characteristic nonlinear signals in the back focal plane.