Fischer, Peer Max Planck Institute for Medical Research, Max Planck Society;
https://journals.aps.org/pra/abstract/10.1103/PhysRevA.64.053816 (Any fulltext)
https://journals.aps.org/pra/pdf/10.1103/PhysRevA.64.053816 (Any fulltext)
Fischer, P., Buckingham, A. D., & Albrecht, A. C. (2001). Isotropic second-order nonlinear optical susceptibilities. Physical Review A, 64(5): 053816, pp. 053816-1-053816-7. doi:10.1103/PhysRevA.64.053816.