G. W. Roland

Laser Properties of Nd +3 and Ho +3 Doped Crystals with the Apatite Structure

A great variety of compounds occur in nature or have been synthesized in the laboratory that crystallize with the apatite structure. We have investigated a number of the apatites and found them to be excellent laser hosts for neodymium and holmium. The apatites described in this paper were grown using the Czochralski method, have low optical losses in the pump and emission spectral regions for neodymium and holmium, and the hosts have been developed to readily accept large concentrations of doping ions. This paper describes the crystal growth, physical properties, spectroscopy, and laser performance of this family of new laser materials.

Optical Properties of a New Nonlinear Optical Material: Tl 3 AsSe 3

We report on the synthesis and the measurement of the properties of large single crystals of a new synthetic nonlinear optical material of the sulfosalt type, Tl(3)AsSe(3). The crystal space group is R3m; the refractive indices range from 3.14 to 3.44 with n(0) - n(e) = 0.18 (negative uniaxial), and the material is transparent from 1.26 microm to beyond 17 microm. The nonlinear optical susceptibilities are of the order of three times those of Ag(3)AsS(3) (proustite), in reasonable agreement with Millers rule, and the measured phase-match angle for frequency doubling of the CO(2) laser output (10.6 microm) is theta(m) = 22 +/- 2 degrees . Calculations of tuning curves for parametric oscillation indicate the possibility of angle tuning over the entire transparency range of the crystal; pumping at 2.06 microm (Ho(3+)-doped YAG or SOAP) appears to be a promising technique for obtaining efficient tunable parametric oscillation in the 3-5-microm region.

Chemical vapor deposition of superconducting Nb3Ge having high transition temperatures

Superconducting films of Nb3Ge have been deposited by chemical vapor deposition. Chloride vapors were produced in situ and reduced by hydrogen. The reactor used allowed surveying of phases with varying Nb/Ge ratio. The highest transition onset temperature was 21.7 K with a transition width of 0.4 K. It occurred near the Ge‐richest boundary of the Nb3Ge phase.

Acousto‐optic properties of some chalcogenide crystals

We report results of extensive measurements on the acousto‐optic properties of several sulfosalt‐type chalcogenide crystals. These materials typically are transparent from the near ir to the intermediate ir, with refractive indices ranging from 2.5 to 3. Their acoustic velocities are among the lowest of any material, and ultrasonic attenuation remains low for frequencies to 500 MHz. These properties lead to exceptionally high acousto‐optic figures of merit.

Optoacoustic properties of thallium arsenic sulphide, Tl3AsS4

We report on the growth and the measurement of optical and optoacoustic properties of Tl3AsS4, a new single‐crystal sulfosalt material. It is transparent from 0.6 to 12 μm, has an optoacoustic figure of merit (relative to fused silica) of over 500 (at 0.6328 μm), and rather low acoustic losses.

Impurity doping of chemical‐vapor‐deposited Nb3Ge and its effect on critical‐current density

In an earlier work, we demonstrated that high self‐field and low‐field critical‐current densitites Jc of the order of 106 A cm−2 can be attributed to flux pinning on a dispersed Nb5Ge3 tetragonal phase present in Nb3Ge3 layers grown by chemical‐vapor deposition (CVD). In this study, we examined the effect of impurity gas additions on Jc and the critical temperature Tc of the A15 superconducting phase. The gas impurities were N2, C2H6, and CO2. The impurity concentration in the gas phase was varied over three to four orders of magnitude to establish tradeoffs between Tc deterioration and Jc enhancement. The x‐ray phase analysis of samples containing the highest impurity concentrations indicated by the presence of niobium nitrides and carbides, respectively. The Tc was affected least by N2 and most by CO2 additions. Doping by N2 or C2H6 resulted in A15 deposits free of the tetragonal phase and having Jc’s of the order of 106 A cm−2, comparable to the best Nb5Ge3‐containing samples. The grain size of deposit...

Phase relations and diffusion layer formation in the systems Cu-Nb-Sn and Cu-Nb-Ge

Condensed phase relations were determined for part of the system Cu−Nb−Sn at 1100 and 1000°C, and for part of the system Cu−Nb−Ge at 1100°C. Diffusion experiments in both systems were conducted at 1100 and ∼800°C. The two types of experiments were compared in order to undertand the diffusion synthesis of superconducting A15 structure compounds from Cu−Ge or Cu−Sn bronzes. Whether an A15 layer of Nb3Ge or Nb3Sn can form by diffusion depends on the orientation of two-phase tielines in the appropriate system. The tielines existing between bronze and Nb3Sn in the Cu−Nb−Sn system are closely followed by the diffusion path inbrozen-Nb diffusion couples so that a super conducting Nb3Sn layer forms. Bronze-Nb3Ge tielines are precluded in the Cu−Nb−Ge system by a two-phase field, Nb−Nb5Ge(Cu) solid solution. Diffusion paths from bronze to Nb do not enter the Nb3Ge phase field and no Nb3Ge diffusion layer forms. The possibility exists that the addition of other chemical components might favorably modify the phase relations such that bronze diffusion synthesis can succeed for Nb3Ge.

Temperature dependence of Jc in superconducting Nb3Ge

Measurements are presented of the temperature variation of the critical current density Jc for superconducting Nb3Ge in the field range 0–65 kG. Samples prepared either by sputtering or chemical vapor deposition (CVD) show a behavior similar to that exhibited by Nb3Sn. The data can be approximated by the relationship Jc∼[Hc2(t)]n. The n values range from 1 for self‐field Jc to 5 at a field intensity of 50 kG.

Temperature dependence of J/sub c/ in superconducting Nb/sub 3/Ge

Measurements are presented of the temperature variation of the critical current density Jc for superconducting Nb3Ge in the field range 0–65 kG. Samples prepared either by sputtering or chemical vapor deposition (CVD) show a behavior similar to that exhibited by Nb3Sn. The data can be approximated by the relationship Jc∼[Hc2(t)]n. The n values range from 1 for self‐field Jc to 5 at a field intensity of 50 kG.

Critical Current Density and Flux Pinning in Nb3Ge

High self‐field critical current densities, Jc, of the order of 106 A/cm2 between 4 and 14 K have been reported for chemical vapor deposited (CVD) films of Nb3Ge. Our results of Jc measurements in a wide field range and film composition analyses suggest that high values of Jc are due primarily to flux pinning on dispersed tetragonal (σ) phase. Single phase (A15) Nb3Ge samples exhibited lower Jc of the order of 104 to 105 A/cm2. The ac loss measurements corroborate the proposed interpretation.