| Summary: | We experimentally demonstrate comprehensive reveal of the ultrafast plasmonic field distribution in a bowtie nanostructure by two-color photoemission electron microscopy (PEEM). We attribute the comprehensive reveal of the field distribution to an effective opening of the two-color quantum channel in multiphoton photoemission, which leads to a dramatic reduction of the nonlinear order (from 4.07 down to 2.01) of the plasmon-assisted photoelectrons and a huge increment of the photoemission yields (typically 20-fold enhancement). Furthermore, we have found that opening extent of the quantum channel strongly related with the photoemission yields generated from one-color 400 and 800 nm laser pulse illumination, and the optimized ratio between the yields for effective opening of two-color quantum channel in our experiment is also achieved. Additionally, benefiting from the high spatial resolution of PEEM, we found there exists a large difference in the nonlinear order of two-color photoemission under the plasmonic excitation within a nanostructure, which has not been reported yet. This work introduces multicolor quantum channel photoemission into the PEEM imaging and offers new way to flexibly control the nonlinear order of the plasmon-assisted photoemission, and it will enable PEEM as a versatile tool in many potential applications.
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