Optical High Harmonic Generation in $\rm \bf C_{60}$

\newcommand{\cm}{$\rm C_{60}$ } \newcommand{\ete}{{\it et al.}} \newcommand{\prl} {Physical Review Letters } \newcommand{\prb} {Physical Review B } High harmonic generation (HHG) requires a strong laser field, but in \cm a relatively weak laser field is sufficient. Numerical results presented here show while its low order harmonics result from the laser field, its high order ones are mainly from the multiple excitations. Since high order harmonics directly correlate electronic transitions, the HHG spectrum accurately measures transition energies. Therefore, \cm is not only a promising material for HHG, but may also present an opportunity to develop HHG into an electronic structure probing tool. References: G. P. Zhang, \prl {\bf 91}, 176801 (2003); G. P. Zhang and T. F. George, \prb {\bf 68}, 165410 (2003); P. B. Corkum, \prl {\bf 71}, 1994 (1993); G. P. Zhang and Thomas F. George, \prl {\bf 93}, 147401 (2004); H. Niikura \ete, Nature {\bf 417}, 917 (2002); {\it ibid.} {\bf 421}, 826 (2003); Y. Mairesse \ete, Science {\bf 302}, 1540 (2003); A. Baltuska \ete, Nature {\bf 421}, 611 (2003).