A theoretical optical physicist who studied the physical mechanisms of second-order nonlinear polarization. His 1962 analysis distinguishes strongly dispersive ionic motion from electronic response far below its resonances. The additional permutation constraints associated with Kleinman symmetry reduce the number of independent response coefficients, but require assumptions about the frequency dependence of the mechanism.[ref]
Nonlinear Dielectric Polarization in Optical Media by D. A. Kleinman. Abstract: ionic versus electronic mechanisms and extra symmetry constraints
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