Materials exhibiting superconductivity above liquid nitrogen temperatures (77 K) will enable new applications of this phenomena. One of the first commercial applications of this technology will be superconducting magnets for medical imaging. However, a large number of aerospace applications of the high temperature superconducting materials have also been identified. These include magnetic suspension and balance of models in wind tunnels and resistanceless leads to anemometers. The development of superconducting wires fabricated from the ceramic materials is critical for these applications. The progress in application of a patented fiber process developed by Clemson University for the fabrication of superconducting wires is reviewed. The effect of particle size and heat treatment on the quality of materials is discussed. Recent advances made at Christopher Newport College in the development of micro-ohm resistance electrical contacts which are capable of carrying the highest reported direct current to this material is presented.

Newly developed technique involving use of gold makes possible to fabricate low-resistance contacts with rugged connections to high-Tc superconductors. Gold diffused into specimen of superconducting material by melting gold beads onto surface of specimen, making strong mechanical contacts. Shear strength of gold bead contacts greater than epoxy or silver paste. Practical use in high-current-carrying applications of new high-Tc materials, including superconducting magnets, long-wavelength sensors, electrical ground planes at low temperatures, and efficient transmission of power.

We have extended our studies of a melting technique for making low-resistance contacts to high-temperature superconductors. We have made contacts to both YBa2Cu3O7−x and Bi2BaSr2Cu2O8, and to related superconducting compounds by melting gold or silver pads onto the samples before the final oxygen treatment. Scanning electron microscope studies show that both gold and silver do not diffuse far from the contact area. The surface contact resistivity of the best contacts made by the melting technique has an upper limit value in the 10−8 Ω cm2 range at 77 K. This contact resistivity shows no significant change in its value over a period of 17 months. Furthermore, an electron radiation dose of 5.7×1017 electron/cm2 only doubled the contact resistivity. This method of making low-resistance contacts to high-Tc materials can be integrated into the final oxygen treatment of many prospective superconducting elements or devices.

We have investigated the effect of 1-MeV electron irradiation up to a total dose of 5.7×1017 electrons/cm2 at room temperature on YBa2Cu3Ox with gold bead contacts made by the melting technique. We measured the superconducting transition temperature Tc, the critical current density Jc at 77 K, the normal-state resistivity, and the contact resistance for gold bead contacts as a function of fluence on the same samples without disturbing the contacts. Tc remained constant at 91 K, and Jc at 77 K remained constant around 90 A/cm2. The normal-state resistivity increased systematically by about 15% for the total dose. Finally, the surface contact resistance at 77 K remained less than 4.2 μΩ cm2 throughout the radiations. These studies took place over an 8-month period, and subsequent measurements indicate that the results are definitely due to radiation effects and not aging effects. Since the total dose represents 120 years of electron exposure in geosynchronous orbit, we conclude that the superconductor YBa2Cu3Ox with gold bead contacts would perform well in a space environment of electron irradiation.

NASA and the international atmospheric science community are committed to the careful and protracted study of the problems associated with global changes in the ecosystem [1-3]. Remote sounding of the atmosphere from space is a nesessary part of this effort. Active remote sensors, those using lasers as a source of probing radiation in light detection and ranging (lidar) measurements, will play a central role in atmospheric sounding [4]. Lidar instruments enable measurements not possible by passive measurement systems and significantly improve upon the accuracy and resolution of passive measurements. The development of these instruments depends, in turn, on the identification and characterization of new materials, on the incorporation of these materials into laser systems and on the development of innovative measurement strategies. The technological products of this research are versatile and can be utilized by other NASA programs. For example, lidar instruments can also be used for doppler lidar measurements of windshear.

Calculations indicate that the thermal stress resistance for diamond is significantly higher than for other materials, suggesting that diamond films may inhibit damage to optical components in laser systems. To assess this possibility we have begun to study laser-induced damage in diamond films. We have measured laser damage thresholds of free-standing diamond film windows, diamond films deposited on silicon substrates, and bare silicon substrate. Polycrystalline diamond films were deposited using a dc plasma-enhanced chemical vapor deposition process. As expected, the free-standing diamond films showed a high laser damage threshold. Melting or dielectric breakdown induced by laser radiation may be the damage mechanism. The film/substrate combination had a damage threshold lower than the calculated value, which is attributed to film stress and conditions of film deposition.

The many unique physical properties of diamond make it useful as a thin film coating for laser optics. We have calculated the laser induced thermal stress resistance for diamond and other optical materials. The calculated stress resistance for diamond is orders of magnitude higher than any other material and, therefore, diamond films should have a higher laser damage threshold. Calculations also indicate that diamond film, because of its high thermal conductivity, exhibits tolerance for isolated impurity inclusions. Polycrystalline diamond films were deposited on silicon substrates using a d.c. plasma enhanced chemical vapor deposition process. The films were characterized by Raman and optical absorption spectroscopy and by ellipsometry. Laser induced damage thresholds of diamond film windows and films on silicon substrates were measured for single pulses of 532 nm and 1064 nm laser radiation. The measured damage thresholds for diamond windows are 6.0 J/sq.cm (300 MW/sq.cm) at 532 nm and 12.4 J/sq.cm (620 MW/sq.cm) at 1064 nm. For diamond on silicon, the damage thresholds are 3.65 J/sq.cm (182 MW/sq.cm) at 532 nm and 14.4 J/sq.cm (720 MW/sq.cm) at 1064 nm. These values compare favourably with those for other common materials used as optical coatings.

An expression for the time-dependent temperature distribution in a finite solid-state laser rod, for an arbitrary distribution of pump energy, has been derived. The specific case of end pumping by circular (constant) or Gaussian beams is included. This formulation was used to predict the time evolution of temperature in Ti:sapphire laser rods and in Nd:YAG rods of specific dimensions.< >

Laser remote sensing from satellites require efficient, long lifetime, maintenance-free tunable lasers and new solid state laser technology is emerging to meet these requirements. This new technology will provide lasers for the medical community capable of tunable operation over a broad wavelength range with factors of ten reductions in size, power and cooling requirements and maintenance costs while remaining competitive in cost with present laser technology.

A simple procedure for extracting the optical absorption and emission spectra of insulating crystal fibers is described. Experimental results are presented for a crystal fiber of Titanium doped Sapphire grown by the laser heated pedestal growth technique. Results of this technique compare well with those obtained from Czochralski grown samples.

Significant differences between the optical spectra taken from sound regions of teeth and carious regions have been observed. These differences appear both in absorption and in laser induced fluorescence spectra. Excitation by the 488 nm line of an argon ion laser beam showed a peak in the emission intensity around 553 nm for the sound dental material while the emission peak from the carious region was red-shifted by approximately 40 nm. The relative absorption of carious region was significantly higher at 488 nm; however its fluorescence intensity peak was lower by an order of magnitude compared to the sound tooth. Implications of these results for a safe, reliable and early detection of dental caries are discussed.

Progress at Stanford University in the development of a LIDAR operating at one micron in a master oscillator power amplifier configuration required a reasonably stable, narrow linewidth laser oscillator. The required stability was achieved by the development of a non-planar Nd:YAG ring oscillator pumped by a ten-stripe diode laser array. Ten kilohertz linewidths are typical for this 300 THz oscillator. The Schawlow-Townes linewidth limit for this laser oscillator is predicted to be 1Hz per milliwatt output. A first time measurement of this linewidth limit for a laser oscillator operating at 300 THz is the objective of a proposed free-flying space experiment.

An analytical study of temperature distribution in actively cooled rods is applied to end-pumped solid-state lasers. The pump is assumed to be a single pulse of a highly focused Gaussian beam whose waist lies close to one end of the rod. High intensity spots cause thermal gradients leading to optical path distortions and stress-induced damage. A hot spot is formed at the position of the pump waist. The hot spot weakens and moves as a result of the active cooling of the rod. Data on the evolution of hot spots in Nd:YAG and Ti:A1203 laser rods are provided.

A new technique for determining the optical properties of insulating single crystal fibers is presented and applied to Titanium-doped Sapphire, Spinel and YALO.