Steering thermal photoassociation of magnesium atoms by two time-delayed femtosecond laser pulses

By solving the full-dimensional time-dependent Schrodinger equation with the thermal-random-phase wavepacket method, we investigate the photoassociation (PA) process of hot (1000 K) magnesium atoms induced by two time-delayed femtosecond laser pulses. Driven by the 840 nm fs laser pulses, the Mg-2 molecules can be formed on the four excited states, (1)(1)pi(g ), (1)(1)pi(u ), (2)(1)pi(u ), and ( 2 )(1)sigma(+)(u) , from the initial electronic ground state X-1 sigma(+)(g) . It is found that the three-photon couplings between X-1 sigma(+)(g) and the three ungerade states [(1)(1)pi(u ) (2)(1)pi(u ), and ( 2 )(1)sigma(+)(u)], play dominant roles in the population transfer process. By scanning the pulse duration tau from 50 to 200 fs, and varying the delay time delta t(0) from 0 to 2 tau fs, we find that the final PA population is strongly dependent on the two parameters. For a given delta t (0), the parameter tau can induce a significant variation (2 similar to 6.8 times) for the final PA population transfer, and for a given tau, one can also obtain a significant variation (2.7 similar to 3.5 times) of the final PA population by varying delta t(0). Additionally, the dynamics of the coherently vibrational wavepackets of the four excited states are also influenced by the two parameters.