That would be angle resolved photoemission spectroscopy (ARPES). Read about it here: https://arpes.stanford.edu/research/tool-development/angle-resolved-photoe

That would be angle resolved photoemission spectroscopy (ARPES). Read about it here: https://arpes.stanford.edu/research/tool-development/angle-resolved-photoemission-spectroscopy https://arpes.stanford.edu/research/tool-development/angle-r... The TL;DR is that you can kick electrons out of a material with light. You can study what comes off and work back to what the electrons were doing in the sample. At the most basic level it tells you "this many electrons were moving in this direction with this energy".