The fluorescence spectra ranging from 400 to 1000 nm were investigated on highly Er(3+) -doped fiber pumped by a 1.48-microm laser diode. A strong green emission was observed. An investigation of the fluorescence intensity dependence on pump power revealed that the green emission is attributed to successive excited-state absorption through a three-step process and also that saturation of the atomic levels that contribute to the emission occurs.

No abstract

Raman scattering by coupled plasmon -LO-phonon modes has been studied in direct-band-gap n-type Al Gal As epitaxial layers with various carrier concentrations. Raman spectra from (100) surfaces of the layers exhibit three branches of the coupled modes whose frequencies and dampings depend on both the carrier concentration and the alloy composition. The dispersion relations of the coupled modes have also been investigated with use of different lines of the excitation lasers, and the wave-vector dependence of the frequencies and dampings have been confirmed. The experimental data agree well with the results calculated by the dielectric-constant method, taking into account the "two-mode" behavior with two sets of the optical phonons in Al"Gal "As. In addition, the carrier-concentration dependence of the coupled mode strength has been calculated with use of the phonon content as a measure, and compared with the observed one.

Using ionized Mg beams accelerated to energies from 130 to 500 eV, Mg doping was studied in molecular-beam epitaxy of GaAs. The incorporation coefficient of Mg increases by a factor of about 100 when compared with the use of neutral Mg beams. Hole concentrations as high as about 1×1019 cm−3 have been achieved. Photoluminescence measurements suggest that the damage due to Mg-ion bombardment is negligible when the ion accelerating voltage (Va) ≲130 V. For higher Va , the damage can be removed by postgrowth annealing.

Wavelength conversions ∼1.5 μm are realized by difference frequency generation in periodically domain-inverted LiNbO3 channel waveguides for the first time. A wide wavelength conversion bandwidth, which is very important for future wavelength division multiplexing optical communication system, is demonstrated in this kind of devices.