Analysis of second harmonic generation from the interface of CuttPc Langmuir-Blodgett film/metal

Optical second harmonic generation (SHG) from the interface of the copper tetra-tert-butyl phthalocyanine (CuttbPc) Langmuir-Blodgett (LB) film / metals has been investigated. In spite of the existence of the inversion center, the enhancement of the signal intensity for CuttbPc/Al sample was also observed. In order to clarify the enhancement mechanism, a four-layer physical model is used to explain the nonlinear optical process. It is considered that the symmetry of the CuttbPc molecule is broken by the space charge induced electric field. The model calculations give a good agreement with experimental results. It was shown that electrostatic phenomena at the interface is correlated closely with SHG signal.