“Probing and controlling the nuclear motion in small molecules with ultrashort laser pulses”


Dr. Uwe Thumm

Physics Department, Kansas State University




The sudden ionization of neutral hydrogen molecules by a short and intense pump laser pulse creates a nuclear wave packet in the molecular ion. This wave packet represents the quantum mechanical generalization of the classical internuclear motion and can be decomposed into a coherent superposition of stationary vibrational states of the hydrogen molecular ion.


Based on numerical simulations, I will discuss possibilities for probing and manipulating the bound motion and dissociation of such nuclear wave packets using a sequence  of  three (or more)  ultra-short (6 fs) and intense (1×1014 W/cm2) near-infrared pump, control, and probe laser pulses. I will address wave packet revivals (that were recently observed and confirmed our predictions) and discuss new numerical results which show that a single control pulse - with an appropriately tuned time delay - can significantly narrow the vibrational state distribution of the  wave packet. A second control pulse can further squeeze the vibrational state distribution, effectively “stopping” the wave packet. This suggests a coherent control scheme that is based on “Raman transitions” induced by time-delayed control pulses: since the resulting nuclear wave function is almost stationary, subsequent fragmentation of the molecular ion with a final intense probe pulse can be used to project its nodal structure onto the measurable kinetic energy release, thereby offering a tool for assessing the degree at which coherent nuclear motion in a small molecule can be controlled.