Duane B. Barber

AMPLIFICATION BY OPTICAL COMPOSITES

Optical amplification is demonstrated in waveguides of composite materials consisting of nanocrystals of Cr:forsterite or Cr:diopside embedded in a host polymer with a matching refractive index. Small-signal gains of 1dB / cm at lambda=1.23microm are reported.

Oxygen activity dependence of the chromium (IV) population in chromium-doped forsterite crystals grown by the floating zone technique

The lasing of Cr-doped forsterite, Cr:Mg2SiO4, at 1.2 μm has been attributed to the presence of Cr4+. The goal of this work was to determine the Cr4+Cr3+ ratios of crystals grown at different oxygen partial pressures and to compare them with a model based on point defect thermodynamics. Cr:forsterite crystals were grown by the floating zone technique with gas atmospheres of 100% Ar, 99% Ar + 1% O2, 80% Ar + 20% O2, 33% Ar + 67% O2, and 100% O2 at 1 atm total pressure. The Cr4+Cr3+ ratios, as well as the distribution of the Cr3+ cations on the M1 and M2 sites, were determined by electron paramagnetic resonance techniques. The fraction of Cr present as Cr4+ ions as a function of the oxygen activity of the growth environment was well described by the model.

Cr/sup 4+/ lasers: present performance and prospects for new host lattices

Cr-doped lasers, based on forsterite and YAG, provide broadly tunable power in the 1.25-/spl mu/m and 1.45-/spl mu/m regions. Performance data on tuning range, pumping, output power, and thermal management for these lasers is reviewed. Potential new crystals for Cr/sup 4+/ should have heavy atoms to reduce lattice phonon frequencies, a distorted tetrahedral cage for the Cr/sup 4+/ ion, and possibly an octahedral site for Cr/sup 3+/. Possible materials include monticellite and diopside. >

Amplification By Optical Composites

Optical amplification is demonstrated in composite materials consisting of nanocrystals of Cr:forsterite or Cr:diopside embedded in a host polymer with a matching refractive index.

Growth of Cr4+-rich, chromium-doped forsterite single crystals by the floating zone method

Abstract Chromium-doped forsterite (Cr:Mg 2 SiO 4 ) single crystals were successfully grown by a floating zone method in an oxygen stream. Bubble formation in the melt zone was effectively avoided by using a premelted feed rod, so that a steady growth was possible to obtain single crystals with a uniform diameter. An after-heater placed just below the melt zone rendered the liquid-solid interface convex toward the melt to prevent the crystals from cracking. The chromium concentration of the grown crystal was almost uniform along the growth direction. Cr:Mg 2 SiO 4 crystals cut perpendicularly to each crystallographic axis show typical pleochroism, i.e., blue, purple and green along the a -, b - and c -axis, respectively. The emission spectra proved that the Cr 4+ to Cr 3+ ratio in the FZ-grown Cr:Mg 2 SiO 4 single crystal was higher than that in a Czochralski-grown crystal.

Amplifiers based on Cr-doped optical ceramics

Broadly tunable solid state lasers in the near infrared can be created using Cr4+ ions doped in various host lattices. Cr:forsterite and Cr:YAG span much of the spectral region between 1.2 and 1.56 micrometers . New hosts are required for powerful operation at 1.32 micrometers . Novel laser structures may be possible using optical nanocrystals embedded in refractive-index matched hosts. Waveguides with net gain are possible using Cr-doped nanocrystals.