Controlling vibrational excitations in C60 by laser pulse durations -: art. no. 147401

Two similar off-resonant ultrafast laser experiments in C-60 have reported two different vibrational modes that dominate the relaxation process: one predicts the A(g) modes while the other the H-g modes. A systematical simulation presented here reveals that this experimental discrepancy results from the laser pulse duration. The numerical results show that since each mode nu has a distinctive optimal duration tau(o)(nu), the A(g) modes are strongly suppressed for durations longer than 40 fs, while the H-g modes start to grow. For the off-resonant and low-intensity excitations, the period Omega(nu)(o) of the dominant mode and tau(o)(nu) satisfy the relation Omega(nu)(o)/tau(o)(nu)approximate to3.4. By carefully scanning the laser frequencies and pulse durations, a comprehensive excitation diagram is constructed, which can be used to guide experiments to selectively excite the A(g) and H-g modes in C-60 by an ultrafast laser. Its potential impact is also discussed.