Light scattering and infrared-transmission spike in multidomain birefringent solids (KCN and NaCN)

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Abstract
KCN and NaCN single crystals, in their low-temperature multidomain structure, are used as model cases for the study of light scattering in polycrystalline birefringent solids. The light-scattering properties, measured over a wide ir range can be fitted to Raman's model, based on the phase shifts of the light in birefringent domains of different orientation, yielding an estimate on the domain sizes. A narrow transmission window in the light-scattering spectrum is observed in the near ir, where the otherwise opaque and light-depolarizing crystal is nearly perfectly transparent and nondepolarizing. This effect can be quantitatively understood as a matching between birefringence from electronic and vibrational excitation, producing an effective optically isotropic behavior of the molecular system at a particular wavelength. Consequences of this birefringence-matching effect for other molecular systems and experimental techniques are discussed.