1. J. Badan, R. Hierle, A. Perigand, J. Zyss, & D. Williams, Nonlinear Optical Properties of Organic Molecules and Polymeric Materials, ACS Symposiyum Series. Am. Chem. Soc. Am. Chem. 233 (1993).
2. D.S. Chemla, J. Zyss, Nonlinear optical properties of organic molecules and crystals, vol. 1 (Academic Press, London, 1987)
3. D. Manivannan, S. Shanmugam, & V. Kavitha, Synthesis, Growth and characterization of 2, 6-Diaminopyridine: phosphoric acid (Dap: Pa) Co-crystals for third harmonic generations. Int. J. Sci. Res. (IJSR), 2319–7064 (2012)
4. N. Numan, S. Jeyaram, K. Kaviyarasu, P. Neethling, J. Sackey, C.L. Kotsedi, M. Akbari et al., On the remarkable nonlinear optical properties of natural tomato lycopene. Sci. Rep. 12, 1–13 (2022)
5. S. Zongo, K. Sanusi, J. Britton, P. Mthunzi, T. Nyokong, M. Maaza, B. Sahraoui, Nonlinear optical properties of natural laccaic acid dye studied using Z-scan technique. Opt. Mater. 46, 270–275 (2015)