The existence of large nonlinear optical coefficients is one of the preconditions for using nonlinear optical materials in nonlinear optical devices. For a crystal. such large coefficients can be achieved by matching photon energies with resonant energies between different bands. and so the details of the crystal band structure play an important role. https://poolsproductscanadas.shop/product-category/hayward-hcp-3000-series-parts/