Thermal conductivity of undoped and Sn-doped β-Ga<sub>2</sub>O<sub>3</sub> bulk and single-crystalline thin films have been measured by the 3ω technique. The bulk samples were grown by edge-defined film-field growth (EFG) method, while the thin films were grown on c-plane sapphire by pulsed-laser deposition (PLD). All samples were with (-201) surface orientation. Thermal conductivity of bulk samples was calculated along the in-plane and cross-plane crystallographic directions, yielding a maximum value of ~ 29 W/m-K in the  direction at room temperature. A slight thermal conductivity decrease was observed in the Sn-doped bulk samples, which was attributed to enhanced phonon-impurity scattering. The differential 3ω method was used for β-Ga<sub>2</sub>O<sub>3</sub> thin film samples due to the small film thickness. Results show that both undoped and Sndoped films have a much lower thermal conductivity than that of the bulk samples, which is consistent with previous reports in the literature showing a linear relationship between thermal conductivity and film thickness. Similarly to bulk samples, Sn-doped thin films have exhibited a thermal conductivity decrease. However, this decrease was found to be much greater in thin film samples, and increased with Sn doping concentration. A correlation between thermal conductivity and defect/dislocation density was made for the undoped thin films.
A new, modulated-pulse, technique is currently being investigated for underwater laser detection, ranging, imag-
ing, and communications. This technique represents a unique marriage of pulsed and intensity modulated sources.
For detection, ranging, and imaging, the source can be congured to transmit a variety of intensity modulated
waveforms, from single-tone to pseudorandom code. The utility of such waveforms in turbid underwater envi-
ronments in the presence of backscatter is investigated in this work.
The modulated pulse laser may also nd utility in underwater laser communication links. In addition to
exibility in modulation format additional variable parameters, such as macro-pulse width and macro-pulse
repetition rate, provide a link designer with additional methods of optimizing links based on the bandwidth,
power, range, etc. needed for the application. Initial laboratory experiments in simulated ocean waters are
We introduce a new beam steering concept of the "Risley grating" that consists of independently rotating inline
polarization gratings (PGs). The Risley grating concept replaces the bulky prismatic elements of the Risley prisms
with thin plates containing polarization gratings, and employs their highly polarization-sensitive diffraction. As
rotating two PGs, the output beam tracks within a field-of-regard (FOR), which is determined by the grating
period and their relative orientations. Since PGs are typically patterned in thin liquid crystal layers (a few μm
thick), the system can be implemented with far less thickness and weight. In addition, these thin gratings can
be placed with virtually zero proximity and the beam walk-off becomes negligible. We demonstrate the Risley
grating that performs continuous steering with 62° FOR and 89-92% transmittance at 1550 nm wavelength. The
governing equations for the steering angles of the Risley grating in the direction cosine space are also presented.
Laser induced Semiconductor Switches (LSS), comprised of a gap antenna deposited on a semiconductor substrate and
photoexcited by a pulsed laser, are the primary source of THz radiation utilized in time-domain spectroscopy (TDS).
THz-TDS applications such as standoff detection and imaging would greatly benefit from greater amounts of power
coupled into free space radiation from these sources. The most common LSS device is based on low temperature-grown
(LT) GaAs photoexcited by Ti:sapphire lasers, but its power performance is fundamentally limited by low breakdown
voltage. By contrast, wide band-gap semiconductor-based LSS devices have much higher breakdown voltage and could
provide higher radiant power efficiency but must be photoexcited blue or ultraviolet pulsed lasers. Here we report an
experimental and theoretical study of 10 wide band-gap semiconductor LSS host materials: traditional semiconductors
GaN, SiC, and ZnO, both pristine and with various dopants and alloys, including ternary and quaternary materials
MgZnO and InGaZnO. The objective of this study was to identify the wide bandgap hosts with the greatest promise for
LSS devices and compare their performance with LT-GaAs. From this effort three materials, Fe:GaN, MgZnO and
Te:ZnO, were identified as having great potential as LSS devices because of their band-gap coincidence with frequency
multiplied Ti:Sapphire lasers, increased thermal conductivity and higher breakdown voltage compared to LT-GaAs, as
well as picoseconds scale recombination times.
In optical fiber evanescent wave sensors, the interaction with the surrounding environment is usually obtained by tapering an optical fiber, which significantly weakens the structure. This paper describes different processes for developing optical fiber probes with gold nanoparticles on the fiber tip including focused ion beam lithography and annealing of continuous gold films by employing plasma arcs, high temperature, or a focused ion beam. Along with the tip based sensors, robust in-line optical fiber sensors were developed by fusing multimode fibers to coreless fibers and forming nanoparticles on the surface of the coreless fibers. The fiber-optic sensors were placed in mediums of different refractive indices to evaluate their chemical sensing capability.
One problem faced by designers utilizing polysilicon based surface micromaching processes is the poor conductivity of polysilicon. Process factors preclude inclusion of metal layers in these processes before the final polysilicon layer is annealed. Adding metal after anneal but before release restricts the metal to only the top layer of the design, making it much less useful for interconnect, and restricting reflective surfaces to the top layer. We present techniques for adding metal after release which avoid some of the usual pitfalls. Application areas for which these techniques could prove useful include RF, Microwave, Optical MEMS, and MEMS devices used in high-speed digital communications. Creating a multilayer metal interconnect is enabled by utilizing a self-masking approach to avoid shorting, and applying e-beam evaporation from a variety of angles. Using this approach, even lower level polysilicon lines can be metallized. Results using two deposition angle recipes on test structures and devices fabricated in a thin film MEMS process are presented.