Fragmentation dynamics of molecular hydrogen in strong ultrashort laser pulses

Abstract

We present the results of a systematic experimental study of dissociation and Coulomb explosion of molecular hydrogen induced by intense ultrashort (7-25 fs) laser pulses. Using coincident recoil-ion momentum spectroscopy we can distinguish the contributions from dissociation and double ionization even if they result in the same kinetic energies of the fragments. The dynamics of all fragmentation channels drastically depends on the pulse duration and for 7 fs pulses becomes extremely sensitive to the pulse shape. 32.80. Rm, 31.90.+s, 32.80.Fb

Real-time observation of vibrational revival in the fastest molecular system

“…This band is due to Coulomb explosion, where, similar to the previous case, both ionization steps can either occur within one pulse (most likely the probe one, see Fig. 3a and 3b For very small delays this band is shifted towards larger proton energies due to the higher laser intensities achieved in case of constructive interference between both pulses [20,[36][37][38][39].…”

“…Whereas the Coulomb explosion peak is more intense than for 3*10 14 W/cm 2 (compare Fig. 3a and 3b), it is still considerably suppressed compared to the case of longer pulses of the same intensity [36][37][38][39][40]. Alternatively, the H 2 + ion, which has been created in the pump pulse and remained bound until the pulse has gone, can be dissociated by the probe pulse: pump: H 2 → H 2 + + e -; probe: H 2 + → H + + H (pathway 1b).…”

“…The 3 eV structure originates from enhanced ionization of H 2 + in the laser field at rather large internuclear distances (4 -6 a.u.) [40][41][42][43] which, for the 6.5 fs pulses used in the present experiments are only reached by the main part of the wave packet when the intensity has already significantly dropped down [36,40].…”

“…The pronounced peak close to 0.3 eV energy with a long tail towards higher values originates from H 2 + dissociation, whereas the broad structure beyond 2 eV is mostly due to Coulomb explosion. Note that the Coulomb explosion peak usually observed at around 3 eV for H 2 (D 2 ) fragmentation in longer pulses of similar intensity [36][37][38][39][40] is strongly suppressed and shifted towards higher energies. The 3 eV structure originates from enhanced ionization of H 2 + in the laser field at rather large internuclear distances (4 -6 a.u.)…”

“…By inspecting momentum conservation for multi-photon single ionization along the jet propagation, its internal temperature was determined to be about 3 K such that D 2 molecules are well prepared in their vibrational ground state before the interaction. A more detailed description of the spectrometer and the coincidence measurement scheme can be found in [35,36].…”