Dendritic sidebranching with periodic localized perturbations: Directional solidification of pivalic acid–coumarin 152 mixtures

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Abstract
We have studied the response of the sidebranches of pivalic acid dendrites, growing by directional solidification, to localized periodic thermal perturbations. The perturbations were generated by a laser beam focused near the tip of a single dendrite growing in a glass capillary, with the pulse duration, repetition rate, and intensity controlled separately. The perturbation dramatically altered the sidebranch structure, producing ordered sidebranches of well-defined wavelength, synchronous with the perturbation, which were strongly correlated on the two sides of the dendrite. The dependencies of the sidebranch amplitude on the frequency of the perturbation and on the distance from the dendrite tip were compared to the predictions of Barber, Barbieri, and Langer [Phys. Rev. A 36, 3340 (1987)] and found to be in qualitative agreement. The value of the selection parameter σ found from these fits to the theory is compared to a value obtained from material parameters also determined in this experiment, and to a value deduced from the initial Mullins-Sekerka instability of the planar crystal-melt interface.