L. G. Van Uitert

Energy Transfer Between Rare‐Earth Ions

Fluorescence quenching effects caused by multipolar energy‐transfer interactions between rare‐earth ions are examined. Transfer between remote ions by way of transitions that are matched in energy appears to be essentially dependent upon concentration alone (e.g., Sm3+ self‐quenching) while transfer by non‐resonant mechanisms can show a strong dependence upon crystal structure (e.g., Eu3+ self‐quenching). Examples of thermally dependent multipolar transfer interactions are also given.

dc Resistivity in the Nickel and Nickel Zinc Ferrite System

The dependence of the resistivities of nickel and nickel zinc ferrites prepared from high purity reagents upon composition and firing temperature has been studied.It has been determined that iron deficient nickel zinc ferrites are of much higher resistivity than iron deficient nickel or zinc ferrites.The iron deficient ferrites prepared, which were fired in oxygen below 1300°C and have Ni:Zn ratios greater than 3:7, show a positive thermoelectric voltage. Other compositions or materials fired above 1300°C have a negative thermoelectric voltage.The effect of excess iron upon resistivity is dependent upon the presence or absence of zinc at temperatures below 1300°C.

High‐Resistivity Nickel Ferrites—the Effect of Minor Additions of Manganese or Cobalt

Nickel ferrite, as ordinarily prepared, has a dc resistivity of 104 to 106 ohm‐centimeters. It has been found that by incorporating small amounts of manganese or cobalt, the resistivities can be increased to 1010 or 1011 ohm‐centimeters. Presumably, replacing Fe++ or Ni+++ with Mn or Co ions eliminates the easy conduction paths otherwise provided by the former ions. Further work is required to elucidate the exact mechanism.

A NEW AND STABLE NONLINEAR OPTICAL MATERIAL

The nonlinear coefficient d31 of K.6Li.4NbO3 is equal to d31 of LiNbO3. Also, the serious problem of optically induced refractive‐index inhomogeneities which has been observed in many nonlinear materials, notably LiNbO3, is not observed in this new material. The electro‐optic half‐wave voltage of this new material is 930 V.

Microwave Elastic Properties of Nonmagnetic Garnets

Investigations on cylindrical rods of yttrium iron garnet (YIG) have shown that the magnetostrictive effect at microwave frequencies makes them effective microwave acoustic transducers, and that a lower bound of the acoustic Q is of the order of 2×105 at 1 kMc/sec. This paper describes measurements of acoustic Qs of nearly this same magnitude obtained with the nonmagnetic yttrium gallium garnet (YGaG) and yttrium aluminum garnet (YAlG). A table is given of the longitudinal and shear acoustic wave velocities, elastic stiffness constants, and elastic isotropy for yttrium gallium garnet and yttrium aluminum garnet. Similar data for yttrium iron garnet by Clark and Strakna are included for reference.

Some characteristics of niobates having “filled” tetragonal tungsten bronze-like structures

Abstract Alkali metal and mixed alkali metal-alkaline earth niobates having “filled” tetragonal tungsten bronze-like structures are of particular interest for electro-optic and nonlinear optic applications. The characteristics of a number of the more useful materials and particularly Ba 2 NaNb 5 O 15 , Sr 2 NaNb 5 O 15 , and K 3 Li 2 Nb 5 O 15 are considered in some detail here.

CONTINUOUS OPTICAL PARAMETRIC OSCILLATION IN Ba2NaNb5O15

A tunable, optical parametric oscillator using a continuous pump is reported. The threshold was measured to be 45 mW of multimode power at .532 μ. The efficiency was found to be 1% with 300 mW of pump power.

CONTINUOUS 0.532‐μ SOLID‐STATE SOURCE USING Ba2NaNb5O15

A continuous 0.532‐μ solid‐state source utilizing the nonlinear material Ba2NaNb5O15 inside the cavity of a 1.064‐μ YAlG:Nd laser has generated 1.1 W of coherent green power. This represents 100% conversion to the green of the available infrared radiation from the YAlG:Nd laser utilized.

ZnCl2 glass: A potential ultralow‐loss optical fiber material

Zinc chloride glass is a potentially useful medium for ultralow‐loss (∼1 dB/103 km) optical fibers for wavelengths in the 3.5–4‐μm region. In this region, intrinsic absorption, scatter, and material dispersion are all expected to be small, and the common fully oxidized transition metal impurities and H2O should exhibit extremely weak absorption as well.

LEAD MOLYBDATE: A MELT‐GROWN CRYSTAL WITH A HIGH FIGURE OF MERIT FOR ACOUSTO‐OPTIC DEVICE APPLICATIONS

Crystalline lead molybdate PbMoO4 has been found to be well suited for acousto‐optical device applications. This material has desirable properties similar to the previously reported α‐iodic acid α‐HIO3. However, PbMoO4, unlike α‐HIO3, is insoluble in water and can therefore be readily fabricated into devices and its optical surfaces do not require protection from the atmosphere. The elastic, photoelastic, optical, and thermal properties of PbMoO4 have been measured. These data have been used in the design of several acousto‐optic devices. An example consisting of a two stage (horizontal and vertical) acoustically driven light deflector is described. Each stage of this deflector has an 80‐MHz bandwidth and can deflect over 50% of an incident laser beam (5145 A) with less than 1 W of electrical drive power.