Hyperpolarizability of hydrogen atom under spherically confined Debye plasma J. K. Saha, T. K. Mukherjee, P. K. Mukherjee and B. Fricke Eur. Phys. J. D, 62 2 (2011) 205-211 Published online: 18 March 2011 DOI: 10.1140/epjd/e2011-10668-4