Second harmonic generation materials

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... 

Materials for Frequency Doubling. Second-order NLO materials can be used to generate new frequencies through second harmonic generation (SHG), sum and difference frequency mixing, and optical parametric oscillation (OPO). The first, SHG, is given in equation 3. 

Table 3. Second Harmonic Generation Coefficients of Inorganic Materials...

Material Second harmonic generation coefficients, pm/V Transparency window, nm... 

Barium sodium niobium oxide [12323-03-4] Ba2NaNb 02, finds appHcation for its dielectric, pie2oelectric, nonlinear crystal and electro-optic properties (35,36). It has been used in conjunction with lasers for second harmonic generation and frequency doubling. The crystalline material can be grown at high temperature, mp ca 1450°C (37). 

Lamberth, C. Murphy, D. M. Mingos, D. M. P. Second Harmonic Generation Properties of Some Coordination Compounds Based on Pentadionato and Polyene Ligands. In Organic Materials for Nonlinear Optics II Harm, R. A., Bloor, D., Eds. Royal Society of Chemistry London, 1991 pp 183-189. 

The first and third order terms in odd powers of the applied electric field are present for all materials. In the second order term, a polarization is induced proportional to the square of the applied electric field, and the. nonlinear second order optical susceptibility must, therefore, vanish in crystals that possess a center of symmetry. In addition to the noncentrosymmetric structure, efficient second harmonic generation requires crystals to possess propagation directions where the crystal birefringence cancels the natural dispersion leading to phase matching. 

Organic Materials for Optical Second Harmonic Generation... 

Non-linear optical interactions occur in materials with high optical intensities and have been used to produce coherent light over a wide range of frequencies from the far infra-red to the ultra-violet. The three wave mixing process is of particular interest as it can be used for optical parametric amplification and optical second harmonic generation (SHG) and occurs in non-centrosymmetric materials. 

Molecular crystals are among the most efficient second- and higher-harmonic generating materials. An external electric field E, upon interacting with a molecule, will induce a dipole moment p. If the field is strong, the response may not be linear, in which case the components of p can be developed in increasing powers of E as described by the expansion (i = 1, 2, 3)... 

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