Second-order susceptibility single-component

Detailed information about the components of the second-order susceptibility y2)(-2w to, w) can be obtained from second harmonic measurements on well-defined samples such as single crystals or oriented thin films, the latter obtained by procedures such as the asymmetric Langmuir-Blodgett deposition technique or electric-field poling of NLO chromophore-doped polymers.31 In the case of single-crystal samples, the second harmonic is... 

In Eq. (9). the vector components of M and H refer to an orthogonal coordinate system fixed in the crystal. Similar to k. the quantities r etc. for single crystals arc in general second order tensors. If powder samples with random orientation of the individual polycrystals arc considered, only the average susceptibility... 

In the nonlinear cases the surface nonlinear susceptibility (SNS) arising from a monolayer of adsorbates is linearly proportional to the surface density of the molecules and the second order molecular polarizability (SMP) averaged over the molecular orientational distribution. Since the SH output in the reflected direction is proportional to the square of SNS the intensity is proportional to the square of Ns. Furthermore, with input and output beam polarizations and geometry properly chosen, the various elements of SNS can be selectively measured by the SH. Consequently in the case that SMP is dominated by a single component along a molecular axis one can then determine the orientation of this axis. 7 Furthermore, for a constant orientational distribution, the SH output can be nulled by properly chosen optical polarization and geometry. 

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