Abstract
Laser-excited photoelectron emission from a variety of materials can provide modulated electron beams of high-current density and brightness. In applications such as lithography and in electron-beam devices where current density is important, the incident laser intensity at the emitter surface will be high, and the photocathode materials properties should be different from those needed, for example, in optical detectors. For process applications it is important that the electron source be unaffected by exposure to air. Thin films of organic materials on metallic substrates are attractive because they exhibit higher quantum yields than most metals, resist oxidation, and have intermediate electronic states which enhance two-photon photoelectric generation. Two-photon emission is interesting because chemically inert surfaces tend to have photoelectric threshold wavelengths below 300 nm, where simple continuous or high-repetition-rate lasers are not yet available. At the high-current (and power) densities required in several applications, use of a nonlinear emission mechanism may not pose additional problems, yet it permits use of more convenient laser wavelengths. The excited singlet or lowest triplet states of dye molecules can serve as the resonant intermediate level in such a process. Our calculations show that for a reasonable choice of parameters it should be possible to generate current densities in the 1–100-A/cm2 range by this method.
© 1986 Optical Society of America
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