Pulse width effect on the dissociation probability of CH_4^+ in the intense femtosecond laser field

The laser pulse width effect on the dis- sociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 1013 W/cm2 was used. The ob- served relative yield of the primary fragment ion CH3+ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation (FAD) model and quasi-classical trajectory (QCT) calculation were ap- plied to predicting the dissociation probability of CH4+. The calculated probability is corrected with the mo- lecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths (≥100 fs). The result is ap- proximately consistent with the experimental observa- tion.

The laser pulse width effect on the dissociation probability of CH4^＋ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 10^13 W/cm^2 was used. The observed relative yield of the primary fragment ion CH3^＋ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation （FAD） model and quasi-classical trajectory （QCT） calculation were applied to predicting the dissociation probability of CH4^＋. The calculated probability is corrected with the molecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths （1〉100 fs）. The result is approximately consistent with the experimental observation.