Third harmonic generation of laser radiation in Fe- and Zn-doped polyvinylpyrrolidone R. A. Ganeev, A. I. Ryasnyansky, M. K. Kodirov, S. R. Kamalov, V. A. Li, R. I. Tugushev and T. Usmanov Eur. Phys. J. D, 20 1 (2002) 129-131 Published online: 28 June 2002 DOI: 10.1140/epjd/e2002-00102-7