Quasi-phase-matching technique

Fig.4. Schematic representation of the different common phase-matching techniques in the k space representation. (ADM) anomalous dispersion (WBM) waveguide birefringence (MD) modal dispersion (QPM) quasi-phase-matching (C) Cerenkov and (CP) counter propagating Cerenkov...

Powder X-ray diffraction patterns are the fingerprint of all crystalline substances. The technique is a rapid and powerful tool for identification of all crystalline compounds, and it is especially valuable in the presence of polymorphs or quasi-isochemical compounds, where chemical techniques cannot be applied. The data collection time of a medium-resolution powder diffraction pattern for identification purposes is typically of the order of 20-30 min. Identification of the unknowns in a compound composed of a few phases is a straight-forward automatic procedure in which the Bragg diffraction peaks in the observed pattern are matched against the reported powder diffraction patterns of all known crystalline substances in the powder diffraction file. Advanced computer software is available for such applications. 

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