Abstract

Irradiation of methane by intense laser fields leads to the production of several molecular ions CH_n^m+ (m = 1, 2 with n = 0 - 4) and atomic fragments such as H_n^m+ (m = 0, 1 with n = 1, 2) as a result of dissociation [1]. Previous studies on methane ionization irradiated by pulses of nanosecond duration [2] showed an absence of the parent fragment $C{H}_4^{+}$ in the time-of-flight (TOF) spectrum. This was explained as a result of the dissociation into the $C{H}_3^{+}$ and a hydrogen atom. On the other hand, when the pulse duration was decreased down to 8 fs [3] all the fragment ions disappeared except for the $C{H}_4^{+}$ and $C{H}_3^{+}$ molecular ions indicating that methane did not have enough time to dissociate after the ionization step. All the aforementioned studies were confined to the fundamental wavelength of 800 nm. In the present work, we extend the study to include the second harmonic field at 400 nm.

© 2019 IEEE