LiNbO second harmonic generation

Only certain types of crystalline materials can exhibit second harmonic generation (61). Because of symmetry considerations, the coefficient must be identically equal to zero in any material having a center of symmetry. Thus the only candidates for second harmonic generation are materials that lack a center of symmetry. Some common materials which are used in nonlinear optics include barium sodium niobate [12323-03-4] Ba2NaNb O lithium niobate [12031 -63-9] LiNbO potassium titanyl phosphate [12690-20-9], KTiOPO beta-barium borate [13701 -59-2], p-BaB204 and lithium triborate... 

M. Yamada, N. Nada, M. Saitoh, and K. Watanabe, First-order quasi-phase matched LiNbOs wave-guide periodically poled by applying an external-field for efficient blue second-harmonic generation. Applied Physics Letters 62(5), 435-436 (1993). 

The NLO materials used so far are mainly inorganic materials, such as quartz, KDP, zinc oxide, LiNbOs, etc. The ions in these inorganic materials are responsible for the NLO properties. The ions have a great mass so that the NLO coefficients of these NLO materials are small at high frequency. Table 6.11 lists elements of the NLO tensors of the Pockel effect and of the second harmonic generation for some widely used NLO materials, Xp and x(d ... 

The nonlinear properties of FLCs attracted considerable attention both from the fundamental and technical points of view [132-134]. Since, in ferroelectric phases the center of inversion is absent (Fig. 7.1), the amplitude of the optical second harmonic generation (SHG) ought to be fairly strong, especially in commercially available FLC mixtures with high spontaneous polarization [133]. Reference [134] shows the ways of designing new FLC substances with the increased molecular second-order hyperpolarizability comparable to that of solid electrooptical crystals such as LINbOs. 

One of the most important functions of the second-order nonlinear optical materials, such as LiNbOs and Pb(Zr,Ti)03 is the second-harmonic generation (SHG). Sol-gel prepared Pb(Zr,Ti)03 converts a laser light of a certain wavelength to the light ofhalfthe wavelength (Boulton, 1992). 

Look up the space groups for these materials and then determine which materials cannot generate second harmonics quartz, LiNbOs, NaCl, H2O. 

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