RUI: Laser Photoelectron Beam Sources

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The goal of this research is to investigate the characteristics of intense electron beam sources based on laser-generated photoelectrons at the surface of an organic thin film on a metal substrate. Recent work has demonstrated that high current densities and large total currents can be generated by laser illumination of conventional photocathodes in ultrahigh vacuum environments, and also that organic thin films can serve as excellent photoelectron sources. The advantages of organic films include greatly reduced vacuum requirements and ease of fabrication. This project will determine the energies, energy spreads, angular divergences, and apparent source sizes of photoelectrons from organic-thin films. The temporal behavior of the emission will be investigated with various laser wavelengths and pulse lengths. Films containing active molecules in a host, and more than one type of active molecule, will be evaluated, as well as coatings of a single material. Substrate effects will also be explored. A kinetic model of the emission process will be developed to explain the temporal and spectral characteristics. The proposed research program is an investigation of new techniques and materials, particularly nonlinear organic thin films, which can be used to generate electron beams of high current density under intense illumination by a laser. Electron beams of high brightness can be used for integrated circuit lithographic exposure, for instruments such as microprobes and electron microscopes; for point- source X-ray generation, and for large scale devices such as accelerators and free electron lasers. Laser-generated results indicate that kiloampere currents can be produced easily. Synchronized emission from multiple emitters as well as optically controlled beam shapes are possible with this technique. Because high current densities and small spot sizes with extremely rapid spot deflection can be achieved, the interaction of these beams with semiconductors should make possible some very useful signal processing and switching applications.