Bulk phase second harmonic generation

Unlike linear optical effects such as absorption, reflection, and scattering, second order non-linear optical effects are inherently specific for surfaces and interfaces. These effects, namely second harmonic generation (SHG) and sum frequency generation (SFG), are dipole-forbidden in the bulk of centrosymmetric media. In the investigation of isotropic phases such as liquids, gases, and amorphous solids, in particular, signals arise exclusively from the surface or interface region, where the symmetry is disrupted. Non-linear optics are applicable in-situ without the need for a vacuum, and the time response is rapid. 

Nanometer scale domain configurations in fe bulk crystals pave the way for a new class of photonic devices. As an example, preliminary calculations show that a uv laser (A = 300 nm) based on second harmonic generation in LiTaC>3 crystal requires a periodic nanodomain superlattice with domain widths of around 700 nm. In addition, the current domain gratings in ferroelectric crystals are suitable only for quasi-phase-matched nonlinear interactions in the forward direction, where the pump and generated beams propagate in the same direction. Sub-micron ferroelectric domain gratings are the basis for a new family of devices based on backward nonlinear quasi-phase-matched optical interactions in which the generated beam travels in a reverse or another non-collinear direction to the incident beam. Non-collinear... 

Second harmonic generation is a useful tool in probing the molecular behaviour at the liquid/liquid interface. While its limitations must be taken into account, particularly over the contributions of the observed signals from the bulk phases and the interrelated contributions of molecular density and orientation distribution, the ability to differentiate molecules at the interface from the bulk, is extremely useful. While the related... 

Phosphates showing a bulk polarization (i.e. ferroelectric phases) may be used for nonlinear optical processes see Nonlinear Optical Materials) such as second harmonic generation and electro-optic switching. KTP (Section 5.2.2) and related phases (NH4T10P04 and KTi0As04) are very efficient nonlinear materials. The ferroic phosphates described above also show nonlinear properties. KDP materials are inferior to KTP types but they find use in electro-optics as they are very transparent over a wide frequency range. 

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