More extensive lists of second-order crystals and their properties can be found in standard reference works ( Sutherland 1996), in manufacturers’ specifications (e.g., Cleveland Crystals Inc., Cleveland, OH, provides data sheets, which may also be obtained at ), and in public-domain databases (e.g., at ).įrom a variety of sources. ![]() The optical properties of some important crystals for use in second-order nonlinear optics are reviewed in Table 1. However, not all crystals with large second-order nonlinearities possess birefringence adequately large for this method to be used, and thus phase matching by means of birefringence imposes further restrictions on the choice of crystals for use in second-order nonlinear optics. Because of the frequency dependence (dispersion) of the refractive indices, the phase matching condition has often been satisfied by using birefringent materials and by allowing the birefringence to compensate for dispersion. Here k 3 is the wavevector of the highest frequency wave, and k 1 and k 2 are those of other waves. ![]() This condition requires that the spatial variation of the nonlinear polarization be synchronous with that of the generated field, or mathematically that Δ k= k 3− k 2− k 1 be much smaller than the inverse of the length, L, of the interaction region. An additional requirement on materials properties is set by the fact that second-order nonlinear optical processes can occur with good efficiency only if a standard phase matching condition is satisfied. This requirement limits the choice of crystals to those of certain symmetry classes. It is well established that only crystals that lack a center of inversion symmetry can possess a nonvanishing second-order susceptibility. Insulating crystals form an important class of second-order nonlinear optical materials.
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