Phase measurements in surface nonlinear optics Final scientific report

This research project has examined various aspects of the phase in nonlinear optics. For example, in optical second harmonic generation (an important technique for probing surfaces) the harmonic signal has a certain phase difference with respect to the input laser beam. Knowledge of this phase allows a more complete understanding and interpretation of the second harmonic (SH) data, enabling correct addition/subtraction of nonlinear susceptibilities when several species contribute to the total SH signal, and also for interpreting orientations of molecules. The measured phase of the second harmonic generation (SHG) signal relative to the input may contain contributions both from the inherent phase of the nonlinear susceptibility (deriving from material resonances) and from geometric factors. In particular, one of the first results of this project was to calculate the phase shift, due to the nonlinear Fresnel factors, imparted when SH light is generated during total internal reflection (TIR). These predictions were later verified experimentally. The most direct method of determining the phase involves creating an interference between the SHG signals of the sample and a reference. SHG interference had previously been demonstrated only for the simplest case (e.g. reflection at an interface between a condensed phase and a gas/vacuum) where the SHG signal is generated collinearly with the input laser at the fundamental frequency. An important goal achieved in this project was to devise and implement SHG interference in the more general 'dispersive' geometries where the SH signal is not collinear with the fundamental. We demonstrate two schemes for SHG interference and phase measurements in the dispersive total internal reflection geometry (TIR) and discuss the advantages and limitations of the two different approaches. As an experimental application, we verified our calculations of the phase shift imparted to the SH light when created during TIR. (orig./HK)Available from TIB Hannover: F97B335 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEGerman-Israeli Foundation for Scientific Research and Development (GIF), Oberschleissheim (Germany)DEGerman