Laser cooling of internal molecular degrees of freedom for vibrationally hot molecules - art. no. 013407

We present an approach to laser cooling of internal molecular degrees of fr eedom for vibrationally hot molecules using a sequence of ultrashort laser pulses. It is assumed that the molecules initially occupy different vibrati onal states with a substantial portion of the molecules being in excited vi brational states. We show that the ultimate aim of increasing the vibration al ground-state population through a reduction of the system's entropy can be achieved through a multistep process. In the first step, we design an ul trashort laser pulse that selectively transfers most of the population of t he excited vibrational states to an excited electronic surface; then the fi eld is switched off and the system allowed to relax until most of the excit ed electronic state population has decayed due to spontaneous emission. By repeating this procedure a few times, the entropy of the system can be subs tantially reduced and the population of the vibrational ground state increa sed considerably, even if the lifetimes of the excited electronic states ar e much greater than the length of a control pulse, i.e., if dissipative eff ects are negligiable on the time scales of coherent control.