A. J. Strauss

Phase Diagram of the Zn‐Cd‐Te Ternary System

The ternary Zn‐Cd‐Te liquidus surface and the pseudobinary CdTe‐ZnTe solidus curve have been determined by thermal analysis of cooling and heating curves, respectively, of homogenized liquid and solid alloy samples. The binary Cd‐Te and Zn‐Te liquidus arrest temperatures are in good agreement with most of the previously published data and confirm the presence of well‐ defined inflections on the metal‐rich and Te‐rich sides of both liquidus curves. The binary interchange energy parameters calculated along each liquidus curve for the regular and quasi‐chemical approximation solution models give essentially similar values for dilute solutions. Near equiatomic composition however, they show values respectively in excess of 200 kcal/mole and less than 40 kcal/mole. The pseudobinary CdTe‐ZnTe liquidus and solidus curves exhibit monotonic and sublinear increases in temperature with increasing ZnTe content. The gap between the two curves remains less than 0.16 mole fraction and shows excellent agreement with the values calculated from the ideal liquidus‐solidus thermodynamic relationship. The ternary liquidus temperatures form a smooth surface with a narrow ridge near the pseudobinary CdTe‐ZnTe composition line and practically degenerate ternary eutectic and boundary lines.

Preparation of superconducting YBa2Cu3Ox thin films by oxygen annealing of multilayer metal films

Superconducting thin films consisting predominantly of YBa2Cu3Ox have been prepared by oxygen annealing of metal films formed by using electron beam evaporation to deposit a three‐layer sequence of Cu, Ba, and Y in nominally stoichiometric proportions, then repeating the sequence five times. For the best superconducting films, which were prepared on yttria‐stabilized cubic zirconia substrates, the onset of superconductivity occurred at 94 K and zero resistivity was observed at 72 K. For the best films prepared on sapphire substrates, the corresponding temperatures were 95 and 40 K.

Crystal growth, spectroscopy, and laser characteristics of Ti:Al/sub 2/O/sub 3/

The vertical-gradient-freeze technique has been used to grow laser-quality Ti:Al/sub 2/O/sub 3/ single crystals. Ti/sup 3+/-Ti/sup 4+/ pairs have been shown to be responsible for the residual infrared absorption. Room-temperature oscillator and amplifier experiments are reviewed. >

Residual infrared absorption in as-grown and annealed crystals of Ti:Al/sub 2/O/sub 3/

Data for as-grown and partially oxidized samples of Ti:Al/sub 2/O/sub 3/ grown by the vertical-gradient-freeze technique show that the residual infrared absorption in these samples is largely due to Ti/sup 3+/-Ti/sup 4+/ pairs. In agreement with this pair model, the residual absorption in as-grown samples has been substantially decreased by annealing in a reducing atmosphere. Data for an as-grown crystal grown by the heat exchanger method indicate the presence of a second mechanism for residual absorption that may set a lower limit on the ratio of this absorption to the Ti/sup +3/ absorption used to pump laser emission. >

Room-temperature continuous-wave operation of a Ti:Al2O3 laser.

Room-temperature cw operation of a Ti:Al(2)O(3) laser has been demonstrated for the first reported time. Laser emission at 770 nm was excited with an all-line Ar-ion laser pump. The maximum output power was 1.6 W. Values of (64 +/- 10)% for the internal quantum efficiency and (2.4 +/- 0.5)% for the round-trip cavity loss are obtained from the thresholds and slope efficiencies measured with 0.7 and 4.9% output couplers. The cavity-loss value places an upper bound of 0.007 cm(-1) on the absorption coefficient of the laser rod for the pi polarization (E ||ĉ) || at 770 nm, compared with 0.73 cm(-1) measured at 490 nm, the peak of the Ti(3+) pump band.

Lateral growth of single-crystal InP over dielectric films by orientation-dependent VPE☆

Abstract Vertical and lateral vapor-phase epitaxial growth of InP by the PC1 3 -InP-H 2 method has been investigated as a function of crystallographic orientation. To study lateral growth, a single-crystal low-index substrate is coated with a phosphosilicate glass (PSG) film, patterned openings are etched in the film along selected directions in the plane of the substrate, and growth conditions are fixed so that nucleation occurs only on the exposed areas of the substrate. When the thickness of the InP epilayers grown in the openings exceeds that of the PSG, these layers seed lateral growth over the PSG. This growth is negligible in low-index directions because of the formation of low-index facets. For higher index directions, significant lateral growth occurs because intersecting low-index facets form corners that act as nucleation sites. Such growth has been utilized to form continuous single-crystal InP layers over patterned PSG films. Lateral growth in polar directions is asymmetric.

Optically induced nonresonant changes in the refractive index of Ti:Al(2)O(3).

Changes in the refractive index of Ti:Al(2)O(3) induced by 10-nsec, 532-nm pump pulses from a frequency-doubled Nd:YAG laser have been measured interferometrically at 632.8 nm for signal polarizations parallel (pi) and perpendicular (sigma) to the c axis. The nonthermal portion of these changes decays on a 3-microsec time scale characteristic of the fluorescence lifetime of Ti(3+). For the sigma polarization, the nonthermal index change is equal to the concentration of excited Ti(3) ions times (4 +/- 2) x 10(-24) cm(3). The change for the pi polarization is lower by a factor of 3.7 +/- 0.6. The average change is consistent with the value estimated from a harmonic oscillator model that considers virtual transitions to a charge-transfer band.

Magnetic and optical measurements on Ti:Al2O3 crystals for laser applications: Concentration and absorption cross section of Ti3+ ions

The optical absorption coefficient of Ti:Al2O3 samples at 490 nm for the π polarization (E∥c) is found to be proportional to the concentration of Ti3+ ions, as determined by measurement of the paramagnetic moment as a function of temperature and magnetic field. The experimental data yield the value σ=(9.3±1.0)×10−20 cm2 for the absorption cross section of Ti3+, the active ion in the tunable Ti:Al2O3 laser, at the peak of the laser pump band.

Diffusion and convection in vapor crystal growth

Abstract The dynamics of diffusion-limited vapor growth are analyzed for three cases: growth of microscopic crystallites immediately following nucleation, growth of crystals when vapor transport from the source is due entirely to diffusion, and growth of crystals when vapor transport is increased by natural or forced convection. In the convection case the rate-determining step is the diffusion of the vapor through a boundary layer in the gas phase adjacent to the growth interface. Forced convection decreases the thickness of this boundary layer and leads to rapid growth. It is shown that in this case the growth rate is proportional to the first power of the concentration difference between the source and the interface, and to the square root of carrier gas velocity. The growth rate expression contains one adjustable constant which depends on the geometry of the system. The stability of the growth interface is analyzed in terms of constitutional supercooling. It is shown that a heat source must be introduced between the source and the growth interface in order for a plane interface to be stable. The use of forced convection permits the introduction of a virtual heat source at the outer edges of the boundary layer. Crystals of iodine and camphor have been grown in a system in which forced convection makes it possible to control both carrier gas velocity and the temperature gradient at the interface. The observed growth rates exhibit the calculated dependence on concentration difference and gas velocity, provided that the interface gradient is suitably adjusted for smooth growth. A maximum smooth growth rate of 4 mm/hr was achieved for iodine and camphor, a value approaching rates of growth from the melt.

Small-signal gain measurement in a Ti:Al/sub 2/O/sub 3/ amplifier

A small-signal single-pass power gain of e/sup 5.2/=180 has been measured for a signal in the pi polarization at 790.7 nm in a longitudinally pumped Ti:Al/sub 2/O/sub 3/ amplifier. A double-pass power gain of e/sup 5.2/ approximately=10/sup 4/ has been attained for the same polarization at 799.8 nm. The ratio of the gain cross sections at 632.8 and 790.7 nm is 1/25. The gain anisotropy at 632.8 nm is g/sub pi //g/sub sigma /=2.3. The lifetime of the upper lasing level decreases with increased pumping, probably as the result of amplified spontaneous emission. >