This paper intends to introduce the reader to a recent method of determining the static quadrupole interaction of isomers in solids: LEMS (level mixing spectroscopy). First of all, the basic principle of level mixing is explained, and it is shown how this phenomenon can be observed in the angular distribution of radiation emitted by the decaying isomer. Furthermore, LEMS is compared to level mixing resonances and time differential perturbed angular distribution. It is shown that LEMS is a very attractive method in cases where high spin states are involved, and for isomers with lifetimes up to several milliseconds.

The synthesis and susceptibilities ~4:) and &) of two series of polymethacrylates functionalized with 4-dialkylamino-4'-cyanoazobenzene and 4-dialkylamino-4'-cyanostilbene dyes are reported. The monomeric dyes were homo-and copolymerized with methyl methacrylate in various ratios, to produce polymers useful for nonlinear optical (NLO) applications. The secondorder nonlinear optical properties of corona-poled aligned polymers were evaluated by second harmonic generation measurements. The , & )results for the azo-dye polymers are in the range of 25-324.esu, depending on the functionalisation degree of the copolymers. The poled films do not show a significant decay in the second harmonic signal after four months. esu, and for the stilbene-dye polymers in the range of 42-57 .

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The synthesis and frequency doubling properties of nonlinear optical chromophore functionalized polystyrene with 4-nitro-or 4-cyano-4'-hydroxyazobenzene, or 2-[2-(4-hydroxyphenyl)ethenyl)-3,5-dinitrothiophene are reported. The polymers with longer spacer length of the side chain chromophore show higher x(2) values, because of a better alignment under poling conditions. Values as high as 23,8. 10-gesu at 1064 nm can be achieved. With a stronger acceptor group (3,5-dinitrothiophene) a value of 22. 10-gesu was achieved for a chromophore content which was even 4 times smaller.

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