The precipitation of oxygen in silicon has been studied in the temperature range 650 to 1050 degrees C using the techniques of chemical etching, IR absorption applied to the 9 mu m band (4.2K), and small-angle neutron scattering (SANS). The IR data and etch pit counts, relating to the number densities of precipitate particles, have been fitted to Ham's theoretical model for the diffusion limited growth of randomly distributed particles. Full allowance is made for the increase in size of the precipitates with increasing time and good agreement is found over the complete period starting from zero time. Values of the diffusion coefficient of oxygen so determined are in excellent agreement with other data obtained by different methods, including SANS measurements at 750 degrees C described in the present work. The combined data give D=0.11 exp(-2.51 eV/kT) cm2s-1. The SANS data also indicate that the precipitates are not spherical in shape after a short initial period, and they show that the initial concentration of particles nucleated decreases with annealing time. The solid solubility cs(T) is determined at each temperature and compared with previous measurements. The authors conclude that the best combination of results leads to cs(T)=2.6*1022 exp(-1.4 eV/kT) down to 850 degrees C. At lower temperatures cs decreases more slowly with decreasing temperature, indicating a possible change in the structure or the form of the precipitated SiO2 phase.

An efficient and powerful technique has been developed to treat the problem of wave propagation along arbitrarily shaped single-mode dielectric waveguides with inhomogeneous index variations in the cross-sectional plane. This technique is based on a modified finite-element method. Illustrative examples were given for the following guides: (a) the triangular fiber guide; (b) the elliptical fiber guide; (c) the single material fiber guide; (d) the rectangular fiber guide; guide; (g) the optical stripline guide.

20 kaSTRACT (Continue on reverie aide II neceaaary and Identify by block number) Coherent optical adaptive«techniques (COAX), have been studied by by analysis, and by computer simulation. The experiments have utiliz experiment, ized a 21channel, visible-wavelength, multidither COAT system, while the computer simulations have dealt with both multidither (outgoing-wave) and phase-conjugate (return-wave) systems. Thermal blooming and turbulence distortions and complextarget effects (speckle-modulations) have been studied. This report summarizes N DD,^N RM 73l473 EDITION OF 1 NOV 65 IS OBSOLETE UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE fWien D«(« Entered) n '} y^y^V) i jn UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGECWion Data Eniarad) X-A: 20. Abstract (continued) $ the status of the 21-channel DARPA/RADC, visible-wavelength, multidither COAT experimental model and associated hardware and its use in the experimental measurements on this contract» .^ompj^r simulation studies of propagation distortion compensation and complex taft^t (speckle) effects are also described RecommenjiatiQas-,ACejnade for future work. ecommenjiaüQas ■MExperimenta Experimental observations with the 21-channel COAT system show that blooming distortions occurring in the first 30% of the focused propagation path can be compensated, leading to roughly a factor of 1.5 increase in peak focused-beam \vKKtf]gnff»,_) Depending on the experimental geometry, however, correction factors /from 1.0 to 4.0 have been observed. Both experimental and computer simulation results have shown that turbulence compensation performance is not degraded by the presence of thermal blooming, even though little blooming compensation may occur. Experimentally, the addition of tracking and focus controls to 18-channe planar-array, COAT phase control had no effect for blooming distortions, but produced some correction for an artificially-generated turbulence alone. The 18-channel phase controls could remove essentially 100,. of the turbulence distortions in most cases where there was no significant wavefront tilt error. omputer simulation of phase-coi,jugate (return-wave) COAT systems has shown almost no blooming compensation. \ In addition, there is some evidence that a return-wave COAT system may redupe the focal-plane irradiance if the blooming distortions become too stronj Experimental measurements of COAT operation with equal transmitter and receiver apertures and semidiffuse, extended-glint scotchlight surfaces have failed to produce any degradation in tht system convergence level, eve^ though significant spurious modulations within the dither band were observed in the COAT receiver.BfExperimental and computer simulation results have shown, however that it is possible to reduce the COAT system convergence level if spurious, multiplicative receiver noise signals are strong enough. Such signals can be produced in a COAT^receiver when the speckle pattern return (the target Signatur^) moves by the COAT receiver. A simple analytical model has been developed tha...

The theory of multidither adaptive optical radar phased arrays is briefly reviewed as an introduction to the experimental results obtained with seven-element linear and three-element triangular array systems operating at 0.6328 microm. Atmospheric turbulence compensation and adaptive tracking capabilities are demonstrated.

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