Lattice hardening

If the host polymer does not have a high glass transition temperature then the structures of polymer and chromophore must be such that post-poling lattice hardening can be carried out to assure thermally stable electro-optic activity [2, 5,50,63,64,110,132-150]. 

Spin Casting, Electric Field Poling, and Lattice Hardening... 

Fig. 42. Multi-chromophore-containing electro-optic dendrimer. After electric field poling and lattice hardening this material yields an electro-optic coefficient of 60 pm/V at 1.55 microns...

Achieving sufficient lattice hardening is important for several reasons in addition to securing necessary thermal stability for the poling-induced electro-optic activity [27-31,100-102]. As noted in the previous section, photochemical stability and optical loss (associated with material processing) are frequently strongly dependent on lattice hardness. 

Haller, M., J. Luo, Hongxian Li, T.D. Kim, Y. Liao, B. Robinson, L.R. Dalton, and A.K.Y. Jen. 2004. A novel lattice-hardening process to achieve highly efficient and thermally stable nonlinear optical polymers. Macromolecules 37 688-690. 

It should be noted that chromophore-chromophore interactions, particularly those leading to nontransient aggregation, will affect the efficiency of latticehardening reactions to be discussed later and will contribute to optical loss if not controlled. The derivatization of chromophores that has been used to improve poling-induced optical nonlinearity also leads to improved thermal stability of pol-ing-induced order realized by lattice hardening and to improved optical transparency due to reduced scattering losses. 

C. Lattice Hardening to Stabiiize Poiing-induced Order... 

Noncentrosymmetric order induced by electric field poling or by molecular self-assembly processes must be stable at the elevated temperatures encountered in device fabrication and operation. Conservatively, this means stability at temperatures on the order of 100 C in general, with precise requirements determined by the particular device application pursued and the device fabrication protocols followed. The requirement of stability at elevated temperatures frequently mandates additional lattice hardening to stabilize induced noncentrosymmetric order. 

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