A semi-relativistic first-order distorted-wave Born theory has been used to calculate differential and integral cross sections for electron-impact excitation of the argon atom to 12 different states in the 3p 5 4s and 3p 5 4p manifolds. The calculations were performed at energies between threshold and 150 eV. Our results show that a single-configuration representation is adequate for these excited states of argon. In general, reasonably good agreement between theory and experiment is found at higher energies for those states which can be excited by a first-order direct transition and mixed results are found for those states which can only be excited by exchange transitions in first order.

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Resonant degenerate four-wave mixing in a number of infrared-absorbing dyes was studied with 160-psec pulses at 1.064 um. Hyperpolarizabilities in the range of 10-44 to 10-42 V-2 m 5 were observed. A theoretical model based on a two-band system is developed that explains the results and permits the prediction of hyperpolarizabilities from the linear spectroscopic properties.

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