Title: An all-optical laser atom trap to study light-atom interactions 

Speaker: Dr. Daniel Fischer（Missouri University of Science and Technology） 

Time: 10:00am, Nov.8 (Friday), 2019 

Place: Room 911, Building 5 

Abstract:  

Understanding the dynamics in systems of several interacting particles is one of the key challenges of physics. Such systems generally cannot be described in closed analytical form as soon as more than two particles are involved. This dilemma is well-known as the "few-body problem" which sets us close limits to accurately predicting a many-particle system's state. Therefore, the advancement of our knowledge of phenomena that emerge due to the complex interplay of several particles requires the joined theoretical and experimental exploration for a wide range of situations. The fragmentation of atoms due to the interaction with charged projectiles, with photon, or with strong external fields represent an ideal test ground of few-body physics for several reasons: First, few-body effects in these systems are ubiquitous and relevant to many research fields and numerous technical applications, particularly in areas such as materials science, quantum chemistry, biological science, and information processing. Second, advanced experimental techniques are available which allow manipulation of the parameters of the few-particle quantum state with a high degree of control and accuracy. Moreover, modern spectrometers enable snapshots to be taken of the state's change over time, allowing details of the state's dynamics to be analyzed.  

At Missouri S&T, there is an experiment in operation that combines the most advanced experimental methods for the control and analysis of atomic few-body systems in a single apparatus: An all-optical laser atom trap is used to cool lithium atoms down to milli-Kelvin temperatures and prepare them in excited and polarized electronic states. The dynamics of the system due to the interaction with single photon or femtosecond laser pulses is then analyzed in a "reaction microscope" allowing the coincident measurements of the momentum vectors of atomic fragments after ionization of the atoms. First experiments on single and multi-photon ionization of lithium have been performed. The low electronic binding energies in the lithium target make electronic transitions optically accessible which e.g. for noble gas atoms can only be driven using synchroton-light sources, free electron lasers, or high-harmic attosecond laser pulses.  The high level of control of the atomic quantum states combined with the excellent momentum resolution enables to study excitation and ionization dynamics in great detail.