Abstract

In determining the nonlinear coefficients of organic materials, it has become customary to ignore the phase shifts they generate. Many results reported so far are found to vary from one to another, for various reasons, including experimental errors. Many organic materials show absorption in the visible region, often near the second harmonic (SH) frequency. This damping often leads to broadening of the electronic transitions; hence nonlinear coefficients become complex in the vicinity of the reasonant frequency. Ignoring this factor may lead to erroneous results, especially in comparing nonlinear optical properties of various materials. Therefore, determination of both the magnitude and the phase of nonlinear coefficients is essential in order to understand the nonlinearity in most of the organic materials. A new method to determine complex microscopic nonlinear coefficients of absorbing organic materials is introduced. This method is based on a third-order nonlinear process known as the electric field induced second harmonic generation (EFISH). The design, construction, and operation of the experimental setup are presented, and experimental errors associated with the traditional EFISH experiment are also discussed.

© 1992 Optical Society of America