Metamaterial-Enhanced Nonlinear Terahertz Spectroscopy H. Y. Hwang, M. Liu, K. Fan, J. Zhang, A. C. Strikwerda, A. Sternbach, N. C. Brandt, B. G. Perkins, X. Zhang, R. D. Averitt and K. A. Nelson EPJ Web of Conferences, 41 (2013) 09005 Published online: 13 March 2013 DOI: 10.1051/epjconf/20134109005