Nonlinear optical techniques for characterization of organic electronic and photonic devices

The turn of this century has undoubtedly brought in tremendous interest in the development of organic electronic and photonic devices. As an aid of understanding the physics behind the device mechanism, various experimental tools are innovated and applied. Herein, various nonlinear optical techniques that are employed towards characterization of these organic material-based devices are reviewed. We describe experimental techniques based on second-harmonic generation (SHG) and sum-frequency generation (SFG) and review some potential applications that basically probe the electric field distribution in the bulk and at interfaces of the electronic and photonic devices. SFG carries information about vibrational spectrum of molecules at the surface, and further analysis of that provides in-depth understanding about their chemical structure and interactions, whereas SHG is sensitive to the electronic spectrum of the interfacial molecules. Thus, a comprehensive study using both of these techniques allows a more complete interfacial characterization of organic devices. Most applications use electric-field-induced SFG (or SHG) to examine the electric field orientation and spatial distribution. Further, time-resolved techniques, such as transient SFG or SHG microscopy, allow direct investigation of the charge carrier motion inside the organic layers under device operation, by probing the change of transient electric field. At the end, we briefly discuss possible directions for further research with these techniques.