Evanescent Mode Photoemission

Both the generation of highly controlled electron beams and the visualization of optical modes in integrated photonic structures remain important challenges in modern nanoscience and photonics. Conventional photoemission sources operate in reflection or transmission geometries where light propagates perpendicular to the emitting surface. In these configurations, photon absorption occurs over depths of ~100 nm to 1 µm, while electrons can escape only from within a few tens of nanometers of the surface, limiting emission efficiency and spatial control. Existing techniques for imaging photonic modes—such as near-field scanning optical microscopy and cathodoluminescence microscopy—also require slow point-by-point scanning and often take hours to map areas of only a few µm².

 

Researchers at Arizona State University and collaborators have developed a new technology based on evanescent mode photoemission that addresses both challenges simultaneously. In this approach, light propagates parallel to an ultrathin photoemissive layer through an integrated waveguide, and the evanescent field excites electrons near the surface. Because absorption occurs along the waveguide rather than through the emitter thickness, the spatial distribution of emitted electrons follows the optical mode structure, enabling electron beam shaping with nanoscale features approaching ~40 nm while simultaneously providing a direct map of guided photonic modes.

 

This novel approach enables precise, efficient, and localized electron emission while also providing a powerful method for visualizing optical modes in integrated photonic devices. The technology offers transformative potential for applications in advanced electron sources, accelerator science, photonic device diagnostics, quantum information technologies, and next-generation lithography.

 

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