Electrooptical applications measurement techniques

Since this chapter is focused on electrooptic materials and two-photon absorption, we will not consider measurement techniques for y and y(31 in detail, but refer the interested reader to Ref. [19]. In this section, we will briefly describe some of the techniques that have been used for the measurement of the two-photon cross-section, d. We first recall that the 2PA behavior of a molecule is characterized by a spectrum entirely analogous to a one-photon absorption (1PA) spectrum. Although, from the point of view of an application at a particular wavelength, measurements of d at only that wavelength may contribute to a figure-of-merit for that application, more generally, to understand structure-property relationships, it is helpful to acquire 2 PA data over as wide a frequency range as permitted by the lasers available and by the onset of 1PA. 

For every nonlinear optical effect, one would expect that there is a measurement technique to characterize it. Not all of NLO effects, however, are subject to measurements that are convenient or informative for comparative purposes or device applications. This section highlights a few of the more common test methods for NLO organic molecules and polymers, and provides references for more detailed explanations of these techniques. Significant omissions here are techniques based on the linear and quadratic electrooptic effect, which are discussed in the article Electrooptical Applications. 

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