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The gain characteristics of an erbium-doped fiber amplifier pumped in the 800 nm band have been investigated in detail. The fiber has a dual shape core and the erbium ions are doped only in the inner core to improve the pumping efficiency. The most efficient pumping wavelength is around 820 nm which is determined by the trade off between the decrease in excited state absorption and the decrease in the absorption coefficient. This pumping wavelength makes it possible to achieve an optical gain as high as 40 dB. The noise figures of Er3+-doped fiber amplifiers pumped in the 800 nm band are 4-5 dB in the 1.5 µm signal wavelength region.

Thicknesses of amorphized layers on Si(100), (110), and (111) wafers resulting from 45° sputter cleaning with Ar+in the energy range from 1 to 5 keV have been determined by analyzing secondary electrons induced by 40 MeV O5+under channeling incidence conditions. Thickness is independent of wafer orientation and increases approximately linearly with Ar+energy up to 35±5 Å for 5 keV Ar+. Since in the analysis an ambiguity associated with the surface condition of undamaged crystal is eliminated, this method is extremely useful for investigating nanometer-thick disordered surfaces.