Characterization of devices, circuits, and high-temperature superconductor transmission lines by electro-optic testing

The development of a capability for testing transmission lines, devices, and circuits using the optically-based technique of electro-optics sampling was the goal of this project. Electro-optic network analysis of a high-speed device was demonstrated. The project involved research on all of the facets necessary in order to realize this result, including the discovery of the optimum electronic pulse source, development of an adequate test fixture, improvement of the electro-optic probe tip, and identification of a device which responded at high frequency but did not oscillate in the test fixture. In addition, during the process of investigating patterned high-critical-temperature superconductors, several non-contacting techniques for the determination of the transport properties of high T(sub c) films were developed and implemented. These are a transient, optical pump-probe, time-resolved reflectivity experiment, an impulsive-stimulated Raman scattering experiment, and a terahertz-beam coherent-spectroscopy experiment. The latter technique has enabled us to measure both the complex refractive index of an MgO substrate used for high-T(sub c) films and the complex conductivity of a YBa2Cu3O(7-x) sample. This information was acquired across an extremely wide frequency range: from the microwave to the submillimeter-wave regime. The experiments on the YBCO were conducted without patterning of, or contact to, the thin film. Thus, the need for the more difficult transmission-line experiments was eliminated. Progress in all of these areas was made and is documented in a number of papers. These papers may be found in the section listing the abstracts of the publications that were issued during the course of the research

Subband gap carrier dynamics in low-temperature-grown GaAs

Measurements of the carrier relaxation dynamics in low-temperature-grown GaAs have been made with a femtosecond-resolution, time-resolved pump-probe technique using a subband-gap probe-beam wavelength. The transient absorption and index of refraction changes have been analyzed using a relaxation model with up to four different excited state populations. The carrier recombination time within the midgap trap states is found to be longer than the subpicosecond free-carrier trapping time. Two time scales are observed for the recombination rate, one of a few picoseconds and one of hundreds of picoseconds, indicating the presence of at least two different trap states for the free-carriers in this material. © 1997 American Institute of Physics.  Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71168/2/APPLAB-70-15-1998-1.pd

LDEF Materials Results for Spacecraft Applications

These proceedings describe the application of LDEF data to spacecraft and payload design, and emphasize where space environmental effects on materials research and development is needed as defined by LDEF data. The LDEF six years of exposure of materials has proven to be by far the most comprehensive source of information ever obtained on the long-term performance of materials in the space environment. The conference provided a forum for materials scientists and engineers to review and critically assess the LDEF results from the standpoint of their relevance, significance, and impact on spacecraft design practice. The impact of the LDEF findings on materials selection and qualification, and the needs and plans for further study, were addressed from several perspectives. Many timely and needed changes and modifications in external spacecraft materials selection have occurred as a result of LDEF investigations

Electro-optic field mapping system utilizing external gallium arsenide probes

External electro-optic probes fabricated from two different crystal orientations of GaAs have been implemented in an electro-optic sampling system that is capable of mapping three independent orthogonal components of free-space electric fields. The results obtained for the radiated field from a microstrip patch antenna by the GaAs probes are compared with results on the same antenna obtained using bismuth silicate and lithium tantalate probes. An 8 μm spatial resolution has also been demonstrated for the electro-optic field-mapping system, and the capability for the system to measure field patterns at frequencies up to 100 GHz has been shown. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70294/2/APPLAB-77-4-486-1.pd

In situ characterization of pin diode waveforms using electro‐optic sampling

In situ measurements of nonlinear waveforms produced by a PIN diode under large‐signal excitation have been performed using ultrafast electro‐optic (EO) sampling.The waveforms were sampled using an EO probe positioned immediately after the diode. These data validate a nonlinear model and improve representation of the waveform across the circuit. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2653–2656, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27119Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93525/1/27119_ftp.pd

A fiber‐mounted, micromachined photoconductive probe with 15 nV/Hz1/2 sensitivity

We report the performance of a micromachined, photoconductive‐sampling probe that is fabricated on low‐temperature‐grown GaAs and mounted on a single‐mode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 μm, and a sensitivity of 15 nV/(Hz)1/2 when integrated with a high impedance, junction field‐effect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probe’s compact cross section makes it ideal for applications as an internal‐node, picosecond‐response, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits. © 1996 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70779/2/APPLAB-69-13-1843-1.pd

Subpicosecond time‐resolved studies of coherent phonon oscillations in thin‐film YBa2Cu3O6+x (x<0.4)

We report the results of the first time‐resolved observation of impulsively generated coherent optical phonon oscillations in the semiconducting cuprate compound YBa2Cu3O6+x (x<0.4). The oscillations, which were probed through time‐resolved transmissivity modulation, had a period of 237 fs at room temperature, corresponding to a Raman active mode of A1g symmetry at 142 cm−1. No oscillations were observed in the superconducting form of Y‐Ba‐Cu‐O either above or below Tc. The amplitude, frequency, and linewidth of this mode were measured over a temperature range from ∼7 K to room temperature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70769/2/APPLAB-58-9-980-1.pd

Space Manufacturing: The Next Great Challenge

Space manufacturing encompasses the research, development and manufacture necessary for the production of any product to be used in near zero gravity, and the production of spacecraft required for transporting research or production devices to space. Manufacturing for space, and manufacturing in space will require significant breakthroughs in materials and manufacturing technology, as well as in equipment designs. This report reviews some of the current initiatives in achieving space manufacturing. The first initiative deals with materials processing in space, e.g., processing non-terrestrial and terrestrial materials, especially metals. Some of the ramifications of the United States Microgravity Payloads fourth (USMP-4) mission are discussed. Some problems in non-terrestrial materials processing are mentioned. The second initiative is structures processing in space. In order to accomplish this, the International Space Welding Experiment was designed to demonstrate welding technology in near-zero gravity. The third initiative is advancements in earth-based manufacturing technologies necessary to achieve low cost access to space. The advancements discussed include development of lightweight material having high specific strength, and automated fabrication and manufacturing methods for these materials

Femtosecond optical absorption studies of nonequilibrium electronic processes in high Tc superconductors

We report the results of femtosecond optical transient absorption experiments performed on the superconducting compounds YBa2Cu3O7−x(x ∼ 0) and Bi2Sr2Ca2Cu3O10+δ(δ ∼ 0) and nonsuperconducting YBa2Cu3O6+y(y<0.4) for sample temperatures ranging from ∼7 K to room temperature. Nonequilibrium heating was found to occur on a subpicosecond time scale. A distinct, dramatic increase in the relaxation time was observed for the superconducting samples as the sample temperature was lowered below the critical temperatures of the respective films. Accompanying the increase in relaxation time was an increase in the peak fractional transmissivity change. No such changes were observed for the nonsuperconducting YBCO sample. We believe the above described behavior is electronic in origin and intimately related to the superconductivity of the compounds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69780/2/APPLAB-57-16-1696-1.pd

Subpicosecond carrier lifetime in GaAs grown by molecular beam epitaxy at low temperatures

Epitaxial GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures is observed to have a significantly shorter carrier lifetime than GaAs grown at normal substrate temperatures. Using femtosecond time‐resolved‐reflectance techniques, a sub‐picosecond (<0.4 ps) carrier lifetime has been measured for GaAs grown by MBE at ∼200°C and annealed at 600 °C. With the same material as a photoconductive switch we have measured electrical pulses with a full‐width at half‐maximum of 0.6 ps using the technique of electro‐optic sampling. Good responsivity for a photoconductive switch is observed, corresponding to a mobility of the photoexcited carriers of ∼120–150 cm2/V s. GaAs grown by MBE at 200 °C and annealed at 600 °C is also semi‐insulating, which results in a low dark current in the switch application. The combination of fast recombination lifetime, high carrier mobility, and high resistivity makes this material ideal for a number of subpicosecond photoconductive applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71318/2/APPLAB-59-25-3276-1.pd