Charles E. Byvik

Coherent laser radar at 1.06 μm using Nd:YAG lasers

A coherent laser radar system operating at the 1.06-μm Nd:YAG laser wavelength has been built and operated. A laser-diode-pumped monolithic ring laser served as the master oscillator. A single flash-lamp-pumped zigzag slab amplified the oscillator output to a power of 2.3 kW. Single-mode optical fiber was used to collect and mix the return signal with the local-oscillator output. Signals from clouds at a range of 2.7 km and from atmospheric aerosols at a range of 600 m were detected.

Rugged low‐resistance contacts to YBa2Cu3Ox

We have made rugged low‐resistance contacts to the high Tc superconductor YBa2Cu3Ox by melting gold beads onto the surface of the material. After retreating the samples in oxygen, we have measured contact resistance <50 μΩ. This allowed a direct current of ≊5 A to pass through the contacts without heating while the sample remained in the superconducting state at 20 K. In this letter we present results of scanning electron microscopy, and measurements of contact resistance, critical current, and shear strength on these contacts. Such contacts will be of practical use in high current carrying applications of the new high Tc superconductors.

Laser induced fluorescence of dental caries

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.

Effects of tensile stress on the R lines of Cr 3+ in a sapphire fiber

We have investigated the spectroscopic properties of a crystalline sapphire fiber unintentionally doped with Cr(3+). We find that tensile stress produces blue shifts of the R lines and changes in their radiative lifetimes and integrated intensities that can be correlated to stress-induced changes of the crystal-field parameters.

Photoelectrochemical Response of Some Layered Chalcogenophosphate Compounds ( MPX 3 )

New photoelectrochemical results for the layered chalcogenophosphate compounds MPX3, FePS3, NiPS3, and SnPS3 are presented. The compounds were grown by iodine vapor transport in quartz ampules from a stoichiometric amount of the elements. Crystals of the layered type up to 10 mm x 10 mm x 0.1 mm were grown. The results of the layered compounds from the MPX3 series show good stability in acid solutions under photoelectrolysis condition. The relatively slow increase in the photocurrent with increasing electrode potential suggests high recombination rates for the photogenerated carriers in these layered materials. It is noted that improvements may be possible by, for example, optimizing the preparation of the crystals and the electrode surfaces.

Layered transition metal thiophosphates (MPX3) as photoelectrodes in photoelectrochemical cells

Abstract Layered crystals of the transition metal thiophosphates were synthesized and characterized for use as photoelectrodes in photoelectrochemical cells. Crystals incorporating tin and manganese show n-type response while those with iron and nickel show p-type response. These materials have a measured indirect bandgap of about 2.1 eV. They show ability to photoelectrolyze water in acid solutions with onset potentials which change in a Nernstian way as the pH of the solution changes. The onset potential is near zero volts versus a saturated calomel electrode at pH 2. At n-type crystals, oxygen could be evolved upon irradiation at underpotentials of 850 mV and at p-type crystals, hydrogen could be evolved at underpotentials of 400 mV, indicating a net gain in energy conversion. All crystals were unstable in basic solution. Liquid junction photovoltaic cells in iodide-triiodide acid solution using these layered materials were also constructed and found to have low efficiencies.

Photovoltage Response to Temperature Change at Oxide Semiconductor Electrodes

A study has been carried out on single crystal electrodes of TiO2, SrTiO3, and alpha-Fe2O3 and polycrystalline WO3 to investigate the effect of cell temperature on the onset potential of n-type oxide semiconductor electrodes. It is found that the change of the onset potential with temperature is due to the potential change across the Helmholtz layer. The amount of this change depends on the point of zero zeta potential (pzzp) of the semiconductor electrode. The possibility of increasing the solar-to-chemical energy conversion efficiency of a photochemical cell by increasing the cell temperature is discussed.

Time dependent temperature distribution in pulsed Ti:sapphire lasers

We derive an expression for the time dependent temperature distribution in a finite solid state laser rod for an end-pumped beam of arbitrary shape. The specific case of end pumping by circular (constant) or gaussian beam is described here. We discuss the temperature profile for a single pump pulse and for repetetive pulse operation. The particular case of the temperature distribution in a pulsed Titanium Sapphire rod is considered.

Laser Damage Of Diamond Film Windows

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.

Spectroscopic analysis of insulating crystal fibers

A new technique for investigating the optical properties of solid‐state laser materials using single‐crystal fibers grown by a laser‐heated pedestal‐growth technique is described. Single‐crystal fiber samples can be prepared more rapidly and less expensively than crystals grown by more conventional methods, however, they are smaller and less uniform making spectroscopic measurements difficult. A simple procedure for extracting the optical absorption and emission spectra of insulating crystal fibers is demonstrated with a titanium‐doped sapphire fiber sample; results are comparable to those from Czochralski‐grown material.