Investigating Laser-Atom Collisions
What is modeling of laser-atom collisions?
Of particular interest is the investigation of electron collisions with a short-lived, laser-excited target atom. Currently, there are two experimental methods for exploration of the electron-excited atom collision process:
The electron-photon coincidence method detects a fluorescence photon from the electron excited state after polarization analysis in coincidence with the inelastically scattered electron that was responsible for excitation.
In the electron-superelastic scattering technique, an atom is optically prepared by a laser of known polarization in an excited state; scattered electrons, which gain energy by collisionally de-exciting the atom, are detected.
Electron-superelastic technique requires a detailed understanding of the laser-atom interaction as a function of laser intensity, laser polarization and laser/atom detunings. It is possible, using Quantum Electrodynamic (QED) theory, to generate equations of motion for atomic operator elements representing atomic populations in the ground and excited state, optical coherences formed between the ground and excited state by the laser, and excited state coherences formed by the laser. The QED model generates closed sets of coupled, first order, linear, homogeneous differential equations. These equations are solved using numeric integration, which can be time consuming.
Once the dynamics of the atomic operators are known, it is theoretically possible to predict the line polarization (K) for linearly polarized excitation, or the optical pumping parameter (K') for circularly Polaris excitation. It is how these parameters vary as a function of laser intensity and detuning that is of particular interest to physicists. Introducing integration over the Doppler profile of the atomic beam introduces another complexity which further lengthens the computing time needed.
How did using EnFuzion help with modeling laser-atom collisions?
How was EnFuzion used?
parameter doppler text select oneof "Non-Doppler" "Doppler"
The following figure shows K and K' plotted as a function of laser intensity and laser detuning at the same time. A third variable, the Doppler width of the atomic beam, can be introduced and, with the current software three-dimensional plots, can now display K and K' as functions of laser intensity, detuning and atomic beam Doppler width. This allows the most detailed presentation of all possible data produced by these computations which covers all experimental conditions currently under investigation.
See [Abramson D., Sosic R., Giddy J. and Hall B., Nimrod: A Tool for Performing Parametised Simulations using Distributed Workstations, The 4th IEEE Symposium on High Performance Distributed Computing, Virginia, August 1995.] for more details.
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