Crystalline powders, second harmonic

Work WJ, Hess KHM et al (2004) Definitions of terms related to polymer blends, composites, and multiphase polymeric materials. Pure Appl Chem 76(11) 1985-2007 Wanapun D, Kestur US et al (2010) Selective detection and quantitation of organic molecule crystallization by second harmonic generation microscopy. Anal Chem 82 5425-5432 Wanapun D, Kestur US et al (2011) Single particle nonlinear optical imaging of trace crystallinity in an organic powder. Anal Chem 83 4745-4751... 

The Kurtz powder technique developed by S. W. Kurtz and T. T. Perry in 1968 offered the first possibility for the determination of nonlinear optical properties of crystalline organic componnds. In comparison with a standard such as quartz or urea, the capability of materials to generate the second harmonic is detected. The pulverized sample is irradiated by a laser and the intensity of frequency-doubled light is measured. As this method is influenced by many factors, such as particle size, it is only semi-quantitative. The results give no precise values for the hyperpolarizability p. A further disadvantage is that the method is limited to molecules that crystallize in noncentrosynunetric space groups. 

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