The valence shell excitations of argon were investigated by an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500 eV, and the transition multipolarities for the excitations of 3p → 3d, 4d, 5s, and 5p were elucidated with the help of the calculated intermediate coupling coefficients using the COWAN code. The generalized oscillator strengths for the excitations to 3p 5 ͑3d ,3dЈ͒, 3p 5 ͑5p ,5pЈ͒, and 3p 5 ͑5s ,4d͒ were measured, and the profiles of these generalized oscillator strength were analyzed. Furthermore, although the present experimental positions of the maxima for the electric-monopole and electricquadrupole excitations in 3p → 5p are in agreement with the theoretical calculations ͓Amusia et al., Phys. Rev. A 67, 022703 ͑2003͔͒, the generalized oscillator strength profiles show obvious differences. In addition, the experimental generalized oscillator strength ratios for the electric-octupole transitions in 3p → 3d are different from the theoretical prediction calculated by the COWAN code.

Relatively low thermal stability of secondorder nonlinear optical (NLO) coefficient due to the relaxation of dipole orientation is a major problem limiting the practical application of these NLO polymers. NLO polymers with suitable T g are always important for optical devices. In the present work a synthetic approach to styrene-(N-(4-hydroxyphenyl) maleimide) copolymer (SHMI) with 4-[N-ethyl-N-(2-hydroxyethyl) amino]-4 0 -nitroazobenzene (DR1) as side chain and chromophores has made it possible to efficiently prepare a NLO polymer. The copolymer with high T g of 2028C has low relaxation of dipole orientation. The maximum optical loss at the optical communication wavelength is less than 0.9 dB. NLO coefficient r 33 is 8.2 pm/V (1550 nm) and its maximum relaxation at room temperature is 18%.

Electron energy loss spectra for the inner shell excitations of atomic lithium are measured at an incident electron energy of 2500eV and scattering angles of 0°, 2°, 4° and 6°. Two optically forbidden transitions of (ls2s2)2 S and (1s2s3S)3s2 S are observed. The generalized oscillator strength ratios for Is{2s2p3 P)2P0 to 1s(2s2p1P)2P0 were determined, and they are independent of the momentum transfer.