Controlling Above Threshold Dissociation Of HD~+ With Femtosecond Laser Pulses

With the development and application of femtosecond laser pulse technology, a lot of interesting strong field phenomena was observed, including above threshold ionization and dissociation, high order harmonic and so on. Many researchers expect to interpret and describe these strong field phenomenain theory. The time-dependent quantum wavepacket method has been used to study the strong field phenomena because of its clear physical picture and rapid computation.The above threshold dissociation dynamics of HD+ in linearly polarized femtosecond laser fields is theoretically studied using the time-dependent wavepacket method including the molecular vibrational and rotational degrees of freedom. Based on the Born-Oppenheimer approximation, the calculations are performed on two electronic states, the ground state 1sσg and the excited state 2pσu, and the energy-dependent distributions of the dissociated fragments resulting from the above threshold dissociation are calculated by using an asymptotic-flow expression in the momentum space.A laser field with a Gaussian pulse envelope, wavelengthλ=800nm and full-width at half-maximumτ=30fs is employed in our calculations. Only two-photon dissociation is observable when the laser intensity is 5.O×1012W/cm2. While the laser intensity is increased to 1.5×1015W/cm2, the dissociated fragments resulting from four-photon absorption dominate the photodissociation process. These results are consistent with the experimental observation of Orr et al. Moreover, the ac-Stark shift caused by the intense laser field can change the kinetic energy spectra of the dissociated fragments, and the molecular rotation and alignment also has some effects on the kinetic energy spectra of the dissociated fragments. The molecular rotation reduces the ac-Stark shift and broadens the peaks of kinetic energy spectra of the dissociated fragments. The intense laser field can effectively align the molecule and increase the probability of the above threshold dissociation. We also control the above threshold dissociation of HD+ by changing the carrier-envelope phase of the modulated laser pulse. The intense laser field also causes the ac-Stark shift which changes the kinetic energy spectra of the dissociated fragments. The above threshold dissociation dynamics process is interpreted in terms of the light-dressed potential or the light-induced potential.