Final Report for Contract N00014-86-C-0598 (Thermo Electron Technologies Corporation)
Abstract
1) Bright photoelectron beams emitted from excimer-laser illuminated LaB6. Lanthanum hexaboride has traditionally been used as a high-temperature thermionic emitter of electrons. This material, whose work function for a sintered multicrystalline composition is nominally 2.6 eV, appears to be a reasonably good photoemitter when irradiated by UV light. A quantum efficiency of .001 was recorded for photoemission at a 193 nm (ArF) incident wavelength. 2) Brightness measurements of electron beams photoemitted from multicrystalline LaB6 and the effects of environmental pressure. LaB6 has been tested as a photoemitter when irradiated by unpolarized UV lasers. For photon energies of 5 eV or less, the material, in a multicrystalline form, is measured to have a quantum efficiency at least an order of magnitude greater than that of simple metals. Maximum currents, from a 1.27 sq cm sample, limited by the available laser power, were recorded to be 52, 36, and 0.9 A at irradiating wavelengths of 193, 248, and 308 nm, respectively. At 193 and 248 nm the corresponding normalized rms brightnesses were 6.7 and 2.6 million A/sq cm-sq rad. 3) Measured Brightness of Electron Beams Photoemitted from Multicrystalline LaB6. Laser- driven semiconductor photoemitters can provide the very bright beams of electrons needed in advanced accelerators. However, these semiconductors are easily degraded in operation. Photoemissive testing of the compound LaB6, which is expected to be a more environmentally rugged material, has shown that under excimer-laser irradiation normalized electron beam brightnesses of 6.7, 2.6 and .15 million A/sq cm-sq rad can be achieved at photon wavelengths, respectively, of 193, 248, and 308 nm. (jhd)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 28, 1989
- Accession Number
- ADA216884