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A simple experimental method for determining the efficiency of second harmonic generation (SHG) using small amounts of dry crystalline powder is described. Contrary to previous techniques, the light scattering effects are explicitly accounted for, and a procedure to eliminate their influence is proposed. The method also permits to assess whether a particular crystal is phase matchable or not. Second-order susceptibility coefficients of eight relevant materials for SHG are determined, and the agreement with the single-crystal data is, in general, fairly good. For polycrystalline ZnSe samples, a situation of the so-called random quasiphase matching is evidenced. V C 2014 AIP Publishing LLC. [http://dx.

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The structure of the incommensurate phase of Rb 2 ZnCl 4 has been determined at 194 K ͑2 K above the lock-in transition͒ within the soliton regime using satellites up to fifth order. The rather anharmonic modulation functions agree with the expected steplike functions supported by theoretical arguments. In addition, the constancy of the ratio between the amplitudes of the fifth-order and first-order harmonics, a relation predicted by theory, indicate the correctness of the model and imply a value of 0.4 for the soliton density n s. A symmetry mode analysis shows that the incommensurate structure is consistent with the one of the lock-in phase in the sense that the displacement pattern of every symmetry mode remains unaltered in the transition except for a global change in the amplitudes.