In nonlinear optics experiments using excitation pulses of widths on the order of one nanosecond or greater, signals arising from slow nonlinear mechanisms of possibly thermal origin may appear in addition to the usually desired contributions from fast processes. To some extent, the presence or absence of a fast nonlinearity can be determined through analysis of the output-pulse shapes, but such studies are not always conclusive, particularly if both fast and slow nonlinear mechanisms are present. This paper describes an experimental method that provides a way of quickly detecting the presence of fast and slow mechanisms as they appear over the duration of the excitation pulses. The method yields information on the strengths of the nonlinearities, their relative signs, and estimates of their response times within a limited range. This approach has been found useful as a screening technique because the fast and slow characteristics of numerous compounds can be quickly assessed with a single apparatus.

© 1991 Optical Society of America

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