G. E. Peterson

Nonstoichiometry and Crystal Growth of Lithium Niobate

Deviations from stoichiometry occurring during the crystal growth of lithium niobate have been studied by 93Nb NMR and by shifts in the ferroelectric transition temperature. The high‐temperature phase equilibria of nonstoichiometric lithium niobate were accurately determined by these techniques together with DTA and crystal‐growth experiments. The congruently melting composition is located at 48.6 mole% Li2O and the solid‐solution region at room temperature extends from 48% to 50% Li2O. The implications of growth at noncongruently melting compositions on the compositional uniformity of lithium niobate are discussed in detail.

Control of the Susceptibility of Lithium Niobate to Laser‐Induced Refractive Index Changes

The origin of laser‐induced refractive changes (laser damage) in LiNbO3 has been identified as iron impurities. Quantitative measurements of the damage were made using holographic techniques as the iron impurity content of crystals was varied. Holographic diffraction efficiencies from as high as 0.44 to lower than 10−6 have been achieved with crystals 0.2 cm thick, using 10 W/cm2 of 5145‐A radiation, both by varying the iron impurity concentration and by varying the valence state of these impurities. The previously observed effects of field annealing, crystal coloration, oxidation and reduction, and the role of OH‐ ions are all accounted for.

Damage‐resistant LiNbO3 waveguides

The photorefractive effect (‘‘optical damage’’) severely limits the application of LiNbO3 in visible wavelengths. We have found that proton exchanged LiNbO3, in which up to 70% of the Li ions are replaced by protons, exhibit no measurable index change with average intensities of visible light up to 5 kW/cm2 or peak pulse intensities of ∼5×108 W/cm2 in the guide. These experiments demonstrate that the photorefractive sensitivity of proton exchanged waveguides is at least four orders of magnitude lower than that of conventional titanium diffused guides. Similar results are obtained with titanium diffused waveguides which are subsequently proton exchanged.

Energy Exchange from Nd3+ to Yb3+ in Calibo Glass

Studies of energy exchange from Nd to Yb in calibo glass were made using the technique of time‐resolved spectroscopy. The rate of energy exchange between the systems was of the order of 3×104/sec, while the quantum efficiency for the process was estimated at 0.6. The mechanism is predominately nonradiative.

Helical resonators containing high Tc ceramic superconductors

Resonators are the single most important ingredient in microwave and radio frequency circuits. We have produced some helical resonators using a bulk Ba2YCu3O7 high Tc ceramic superconductor. These resonators, which operate at 77 K and cover the frequency range from 0.1 to 2.0 GHz, outperform their all copper counterparts by at least a factor of 5 in unloaded Q.