1. K. MOLLMANN, W. GELLERMANN and H. WELLING, in XVIII International Quantum Electronics Conference IQEC'92, 14?19 June 1992, Vienna, Austria (Tech. Univ. Wien, Vienna, Austria, 1992) paper MoD4.
2. M. T. ASAKI, C.-P. HUANG, D. CARVEY, J. ZHOU, H. C. KAPTEYN and M. MURNANE, Opt. Lett. 18 (1993) 977
3. C. EDELSTEIN, E. WACHMAN, L. K. CHENG, W. R. BOSENBERG and C. L. TANG, Appl. Phys. Lett. 52 (1988) 2211.
4. S. L. SHAPIRO, Topics in Applied Physics: Ultrafast Light Pulses, Picosecond Techniques and Applications (Springer-Verlag, Berlin, 1977) pp. 18?36.
5. W. MÜCKENHEIM, P. LOKAI, B. BURGHARDT and D. BASTIG, Appl. Phys. B 45 (1988) 259.