Laser-induced Alignment and Coulomb Explosion of CO2

Dynamic processes of CO₂ are experimentally studied in intense femtosecond laser fields with laser intensity varying from 1×10¹³W/cm² to 6×10¹⁴W/cm². When the laser intensity is below the ionization threshold, a coherent rotational wave-packet is formed for CO₂ at room temperature through nonadiabatic rotational excitation. The evolution of the wave-packet leads to transient alignment. The field-free alignment revives periodically after the laser pulse is over. The revival structure can be modified by a second laser pulse for the rotational wave-packet through precisely adjusting the time delays between the two laser pulses. When the laser intensity excesses the ionization threshold, ionization and Coulomb explosion occur. The atomic ions C^m+ (m=1-3) and Oⁿ⁺ (n=1-3) observed in the experiment exhibit highly anisotropic angular distributions relative to the laser polarization. Using two linearly polarized laser pulses with crossed polarization, we conclude that the anisotropic angular distribution results from dynamic alignment, in which the rising edge of the laser pulse aligns the neutral CO₂ along the laser polarization direction prior to ionization.