One of the unique capabilities at LSU is our ability to acquire angle-resolved photoemission data using an ellipsoidal-mirror analyzer. This is one of only a handful in the world.
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One of the unique capabilities at LSU is our ability to acquire angle-resolved photoemission data using an ellipsoidal-mirror analyzer. This is one of only a handful in the world. |
 | This instrument is based on an ellipsoidal mirror which has 2 focal points. The sample is placed at one focal point. Trajectories from this point reflect off the mirror and are refocused at the second focal point. For charged particles the first reflection is a low-pass energy filter. The second focal point is the center of a retarding-grid analyzer which is a high-pass energy filter. Together, these filters give energy analysis and the instrument preserves the angular information. This angular information can be related to the k-vectors of the initial states of the solid that are excited.
Photoemission corresponds to a transition from an occupied electronic state in reciprocal space to a final state wave that is higher in energy by hv. A plane-wave final state often gives good correspondence between measured and calculated band structures. In reciprocal space, a plane wave can be emitted in any direction and its k-vector defines a sphere. |
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Where ever the final-state sphere intersects occupied initial states one can get transitions, giving intensity in the corresponding emission directions. The photon polarization relative to the initial and final states will modulate the matrix element (or intensity) of the transition. |