[1] [1] M. S. Sherwin, C. A. Schmuttenmaer, and P. H. Bucksbaum, "DOE-NSF-NIH Workshop on Opportunities in THz Science" http://www.er.doe.gov/bes/reports/files/THz rpt.pdf.

[2] [2] B. E. Cole, J. B. Williams, B. T. King, M. S. Sherwin, and C. R. Stanley, Nature 410, 60 (2001).

[3] [3] H. Hamster, A. Sullivan, S. Gordon, W. White, and R. W. Falcone, Phys. Rev. Lett. 71, 2725 (1993).

[4] [4] Z.-M. Sheng, K. Mima, J. Zhang, and H. Sanuki, Phys. Rev. Lett. 94, 095003 (2005).

[5] [5] Z.-M. Sheng, K. Mima, and J. Zhang, Phys. Plasmas 12, 123103 (2005).

[6] [6] Z.-M. Sheng, H.-C. Wu, K. Li, and J. Zhang, Phys. Rev. E 69, 025401(R) (2004).

[7] [7] H.-C. Wu, Z.-M. Sheng, and J. Zhang, Phys. Rev. E 77, 046405 (2008).

[8] [8] W. P. Leemans, C. G. R. Geddes, J. Faure, Cs. Toth, J. van Tilborg, C. B. Schroeder, E. Esarey, G. Fubiani, D. Auerbach, B. Marcelis, M. A. Carnahan, R. A. Kaindl, J. Byrd, and M. C. Martin, Phys. Rev. Lett. 91, 074802 (2003).

[9] [9] D. J. Cook and R. M. Hochstrasser, Opt. Lett. 25, 1210 (2000).

[10] [10] M. Kress, T. Lof°er, S. Eden, M. Thomson, and H. G. Roskos, Opt. Lett. 29, 1120 (2004).

[11] [11] T. Bartel, P. Gaal, K. Reimann, M. Woerner, and T. Elsaesser, Opt. Lett. 30, 2805 (2005).

[12] [12] X. Xie, J. Dai, and X.-C. Zhang, Phys. Rev. Lett. 96, 075005 (2006).

[13] [13] X.-Y. Peng, C. Li, M. Chen, T. Toncian, R. Jung, O. Willi, Y.-T. Li, W.-M. Wang, S.-J. Wang, F. Liu, A. Pukhov, Z.-M. Sheng, and J. Zhang, Appl. Phys. Lett. 94, 101502 (2009).

[14] [14] K. Y. Kim, J. H. Glownia, A. J. Taylor, and G. Rodriguez, Opt. Express 15, 4577 (2007).

[15] [15] W.-M. Wang, Z.-M. Sheng, H.-C. Wu, M. Chen, C. Li, J. Zhang, and K. Mima, Opt. Express 16, 16999 (2008).

[16] [16] C. D'Amico, A. Houard, M. Franco, B. Prade, A. Mysyrowicz, A. Couairon, and V. T. Tikhonchuk, Phys. Rev. Lett. 98, 235002 (2007).

[17] [17] Y. Liu, A. Houard, B. Prade, S. Akturk, A. Mysyrowicz, and V. T. Tikhonchuk, Phys. Rev. Lett. 99, 135002 (2007).

[18] [18] A. Houard, Y. Liu, B. Prade, V. T. Tikhonchuk, and A. Mysyrowicz, Phys. Rev. Lett. 100, 255006 (2008).

[19] [19] W.-M. Wang, Z.-M. Sheng, X.-G. Dong, H.-W. Du, Y.-T. Li, and J. Zhang, J. Appl. Phys. 107, 023113 (2010).

[20] [20] H. C. Wu, J. Meyer-ter-Vehn, and Z. M. Sheng, New J. Phys. 10, 043001 (2008).

[21] [21] A. L. Cavalieri, E. Goulielmakis, B. Horvath, W. Helml, M. Schultze, M. Fieb, V. Pervak, L. Veisz, V. S. Yakovlev, M. Uiberacker, A. Apolonski, F. Krausz, and R. Kienberger, New J. Phys. 9, 242 (2007).

[22] [22] E. Goulielmakis, M. Schultze, M. Hofstetter, V. S. Yakovlev, J. Gagnon, M. Uiberacker, A. L. Aquila, E. M. Gullikson, D. T. Attwood, R. Kienberger, F. Krausz, and U. Kleineberg, Science 320, 1614 (2008).

[23] [23] W.-M. Wang, S. Kawata, Z.-M. Sheng, Y.-T. Li, and J. Zhang, Phys. Plasmas 18, 073108 (2011).

[24] [24] M. V. Ammosov, N. B. Delone, and V. P. Krainov, Sov. Phys. JETP 64, 1191 (1986).

[25] [25] W.-M. Wang, S. Kawata, Z.-M. Sheng, Y.-T. Li, J. Zhang, L. M. Chen, L. J. Qian, and J. Zhang, Opt. Lett. 36, 2608 (2011).