Evaluation of hyperpolarizability by Hyper-Rayleigh scattering with ns-laser Excitation.

Abstract

A novel dual measurement system was constructed to evaluate hyperpolarizability β at the excited state of molecules in solutions. The system is based on nano-second (ns) Hyper- Rayleigh Scattering (FIRS) method with CW laser excitation. Optical enhancement and control of the nonlinear optical (NL0) properties of organic compounds can be expected at the excited state due to changes in dipole moments and oscillator strength caused by electron density distribution different from that at the ground state. In the HRS technique, a chromophore solution was irradiated by ns Nd:YAG laser of various intensities (frequency ω), and the scattered photons at 2ω were detected. The HRS intensity was proportional to the square of the incident laser intensity. The HRS signal was usually very weak and contained dark-noise. The dual HRS detection system dividing the Nd:YAG laser into two parts improved the signal/noise (S/N) ratio of HRS signals under excitation. The MRS measurement for p-nitroaniline was observed in methanol and 1, 4-dioxane solutions upon excitation with and without CW Ar laser at 457.9nm.