Coherent Control of Ultrafast Bond Making and Subsequent Molecular Dynamics: 
Demonstration of Final-State Branching Ratio Control

Abstract

Quantum coherent control of ultrafast bond making and the subsequent molecular 
dynamics is crucial for the realization of a new photochemistry, where a shaped 
laser field is actively driving the chemical system in a coherent way from the 
thermal initial state of the reactants to the final state of the desired 
products. We demonstrate here coherent control over the relative yields of Mg2 
molecules that are generated via photoassociation and subsequently photodriven 
into different groups of final states. The strong-field process involves non-
resonant multiphoton femtosecond photoassociation of a pair of thermally hot 
magnesium atoms into a bound Mg2 molecule and subsequent molecular dynamics on 
electronically excited states. The branching-ratio control is achieved with 
linearly chirped laser pulses, utilizing the different chirp dependence that 
various groups of final molecular states display for their post-pulse population.
Our study establishes the feasibility of high degree coherent control over 
quantum molecular dynamics that is initiated by femtosecond photoassociation of 
thermal atoms.