Archibald W. Smith

The tungsten bronze field in the system K2O|Li2O|Nb2O5

A limited portion of the liquidus field and the entire subsolidus stability region has been determined for tungsten bronze-type solid solutions in the K2O|Li2O|Nb2O5 system. The tungsten bronze phase does not occur with completely filled alkali cation sites at the composition K3Li2Nb5O15, but exists exclusively in the high niobia region above the KNbO3|LiNbO3 pseudojoin. Equilibrium relationships defining conditions for the growth of electrooptic crystals, and dielectric, optical, and x-ray measurements establishing the influence of composition on structure and properties are presented and discussed.

Injection Laser Writing on Chalcogenide Films

The crystallization and amorphization of Te-As-Ge films with GaAs injection lasers has been investigated. Power density measurements for crystallization and amorphization are presented, and a reverse-mode write-read-erase cycle is demonstrated. The results show that direct bit storage is feasible with an injection laser-chalcogenide film system.

FERROELECTRIC AND OPTICAL PROPERTIES OF KSr2Nb5O15

A new transparent tetragonal crystal, KSr2Nb5O15, of the tungsten bronze type has been found to be ferroelectric with a Curie temperature of ≈160°C. At room temperature the electro‐optic coefficient, r∥, is 1.3 × 10−8 cm/V and e∥ is approximately 1,000.

Optical storage in VO2 films

The use of VO2 films for direct‐bit optical storage with near‐infrared lasers is demonstrated. The VO2 response is fast (< 10 ns), and large read signals are obtained with unpolarized light. A writing threshold of 0.03 nJ/μm2 is observed.

Degradation‐induced microwave oscillations in double‐heterostructure injection lasers

Microwave oscillations in the light output of mesa‐stripe GaAs–Ga1−xAlxAs double‐heterostructure lasers have been observed after degradation. The same lasers showed no oscillations before degradation. The experimental evidence indicates that the oscillations are caused by repetitive Q switching, with dark‐line regions in the degraded units acting as saturable absorbers.

Oxygen-implanted double-heterojunction GaAs/GaAlAs injection lasers

We describe a new process for stripe formation in double-heterostructure GaAs/GaAlAs injection lasers. This process, which uses oxygen-ion implantation to form the stripe through a chemical doping effect, has several advantages over alternative methods, both with respect to device processing and device properties and has produced high yields of CW room-temperature lasers. We present the details of the device structure and fabrication processes. The results of annealing studies, optical measurements, and lifetesting are described.

Nonlinear Optical Properties of Potassium‐Lithium Niobates

Crystals of composition (K2O)0.3(Li2O)0.7‐x (Nb2O5)x with x in the range 0.515 to 0.55 have useful and unique nonlinear optical properties. These are transparent ferroelectric crystals having the tetragonal tungsten‐bronze structure. Thus, they do not have to be detwinned, as does NaBa2Nb5O15. The dc halfwave voltage is about 1350 V at 6328 A, and the nonlinear constant d31 is 1.7d31 (LiNbO3). For x=0.515 the birefringence is very large. Thus, the phase‐matching temperatures for harmonic generation without double refraction with the Nd‐YAG laser is 450°C. For x=0.55, 140°C is obtained. With these crystals the GaAs injection laser emitting 0.90 μ can be phase matched above room temperature for the first time without double refraction.

Properties of new and useful tungsten-bronze niobates

It is experimentally shown that the electrooptic properties of the ferroelectric phase of the new tungsten-bronze compositions can be treated as a biased quadratic electrooptic effect g_{ij) . This is done by directly measuring the electrooptic behavior above the transition temperature in KSr 2 Nb 5 O 15 . A term linear in electric field is not found. Thus the crystal has a center of inversion. We find g_{33} - (n_{1}/n_{3})^{3}g_{13} = 0.10 m4/C2. This value is very similar to that obtained for a number of compounds containing NbO 6 and similar octahedra. This value is also in good agreement with the effective room-temperature linear electrooptic coefficient r c , if it is assumed that r c can be considered to arise from a biased quadratic effect. Then we use these considerations systematically on other tungsten-bronze ferroelectrics, KSr 2 Nb 5 O 15 , NaBa 2 Nb 5 O 15 , Sr 0.25 Ba 0.75 Nb 2 O 6 , and Sr 0.5 Ba 0.5 Nb 2 O 6 . We calculate g 33 and g 13 separately and also find g_{33} - (n_{1}/n_{1})^{3}g_{13} = 0.10 - 0.11 m4/C2for all of these materials. Thus all these ferroelectrics give similar values to those found elsewhere for oxygen octahedra compounds. We also calculate values for the spontaneous polarization or the induced change in the indices of refraction.

DIFFRACTION OF LIGHT BY MAGNETOELASTIC WAVES

Diffraction of light at 1.15 μ has been observed from magnetoelastic waves at 1.1 GHz in YIG. A shift in the Bragg diffraction angle was observed when an external magnetic field was varied so as to change the spin wave admixture. The largest shift obtained experimentally was ‐2.0°, measured from the elastic limit of 9.5°. This shift was accompanied by a delay in the diffracted pulse of about 1 μsec. Under quasielastic conditions the diffracted intensity exhibited a series of maxima as the field was swept, due to magnetoelastic Faraday rotation.

Radiative lifetime in GaAs1−xPxp‐n junctions

The radiative lifetime in GaAs1−xPx light‐emitting diodes is observed to increase from 2 to 11 nsec with increasing injection level. A related increase in quantum efficiency is also observed. These observations are explained by using a trap‐filling model, where the traps arise from defects in the epitaxially grown GaAs1−xPx.