David L. Begley

Propagation distances of surface electromagnetic waves in the far infrared

Abstract The propagation distances, L x , of surface electromagnetic waves on metal-air and semiconductor-metal-air systems were measured using the two prism technique in the far infrared (84.2 cm −1 ). Copper, gold, palladium, tungsten, nickel, steel, and platinum metal-air interfaces were studied. Also semiconductor-metal-air systems consisting of Pt films of varying thickness deposited on single crystal GaAs substrates were examined. The experimental values for L x were found to be orders of magnitude lower than theoretical values for these metals.

Propagation distance of surface electromagnetic waves on two metal-oxide-air systems☆

Abstract The propagation distance of surface electromagnetic waves on a copper-cuprous oxide-air system was measured using two prism couplers, for oxide thickness between 20 A and 2000 A, and wavelengths from 9.2 μm to 10.8 μm. The copper sample consisted of an evaporated copper film on glass, with an oxide film overlayer grown by heating in air. The measured values of propagation distance agree well with computer-calculated solutions of the three-media dispersion relation. Similar measurements made on a polished surface of rolled titanium, oxidized by heating in air, give agreement only to within 50%. Auger analysis indicated that a carbide impurity on the highly reactive titanium surface and a variation of the titanium oxide composition with thickness both contributed to the disagreement between measured and calculated values of propagation distance.

Propagation distances of surface electromagnetic waves on Ni, Pd, Pt, and W metal surfaces☆

Abstract The propagation distances, L x , of surface electromagnetic waves (SEW) on Ni, Pd, Pt, and W were measured using the two-prism coupling technique at wavelengths from 9.3 to 10.6 microm. Metal samples consisted of films, deposited on glass substrates by electron beam deposition, and metal foils. The measured L x values for the Pd and Pt firms and Pt foil agree to within 20% of the calculated values from the two-media dispersion relation. The measured values of the propagation distance for the Ni film and foil and the W foil agree to within 50% of the calculated L x . Scanning electron microscope (SEM) photographs and Auger analysis indicate that film imperfections and foil surface roughness contributed to the lower propagation distances observed for Pt and Pd while imperfections, roughness, and oxidation contributed to the disagreement between measured and calculated propagation distance for Ni and W.

Optimization of prism coupling efficiency for surface electromagnetic wave excitation in the infrared

The ir SEW coupling efficiency of a BaF(2) prism has been determined for various gap heights and internal angle configurations, utilizing the two prism coupling technique and a CO(2) laser. Samples consisted of W foil and Ni, Pt, and Cu films deposited on glass substrates by electron beam deposition and vacuum evaporation. Optimum prism coupling gap heights were found to occur for each metal. It was determined that selection of the proper internal prism angle increases coupling efficiency by a factor of 3 over the coupling efficiency of the right angle prism.

Aperture shared laser diode array beam combiner

An array of discrete semiconductor lasers utilizing graded-index rod lenses as collimators were fabricated to form a noncoherent laser beam combiner. Continuous wave output power of 600 mW and 5.25% total efficiency were achieved in a 5-mrad beam from a ten-diode laser array. A technique of dichroically combining five arrays is also described.

Propagation of surface electromagnetic waves on n-type GaAs in the far infrared

Abstract The far infrared (84.2 cm −1 ) propagation distance of surface electromagnetic waves on samples of single crystal GaAs with varied carrier concentrations has been measured using the twoprism technique. The experimental propagation distances agree well with theoretical values obtained from computer calculations using the exact two media dispersion relation. It was found that the propagation of the SEW is strongly dependent upon the free carrier concentration of the GaAs sample as expected. It is demonstrated that a simple classical theory of SEW works for GaAs-air interfaces in the far infrared.

Surface electromagnetic wave coupling efficiencies for several excitation techniques

The excitation efficiencies for coupling surface electromagnetic waves onto aluminum at a microwave frequency (f = 8.445 GHz, lambda = 3.55 cm) were studied experimentally for several different standard microwave techniques as well as two optical techniques (prism and grating) applied to the microwave frequency region and two new techniques (hump and valley). The peak measured efficiencies found were: for the standard rectangular waveguide, 92%; for the horn antenna, 73%; for the right angle prism properly gapped above the metal, 60%; for the hump of 10-wavelength radius of curvature, 35%; for the thin grating strips on polystyrene coated metal, 30%; for the grating bars gapped (1/2) wavelength above the metal, 26%; and, for the valley of 10-wavelength radius, 12%. The measurement of the excitation efficiencies for prism and grating coupling techniques sometimes required that the prism or grating be in the near field of the antenna. In addition to measuring peak efficiencies, the efficiencies were measured as functions of the gap heights, the angular orientations, the different diffraction modes, the shapes, and the materials of the grating bars. The coupling efficiencies for both prism and grating couplers show a strong dependence on gap height above the metal. Dielectric grating bars were found to be inefficient compared to solid or hollow metallic bars, or thin metallic strips. The distance between the target point of the center line of the microwave horn antenna and the corner of the prism was found to be about 1 wavelength for maximum prism coupling efficiency.

Two-dimensional optics with surface electromagnetic waves

Two-dimensional optical effects were observed for surface electromagnetic waves (SEW) on metals at lambda = 3.55 cm. Refractive processes with prisms and lenses established Snells law experimentally. Reflection with prisms and metal sheets established the law of reflection and indicated that radiative losses were small and that Fresnels equations hold to a good approximation for the reflectivities of SEW. A two-dimensional SEW grating was made and first-order diffraction observed. Although the experiments were performed at microwave frequencies, the principles are usable for two-dimensional SEW optics at least as far as the near ir. It was shown that the propagation constant of the SEW with an overlayer material is as though the SEW propagates entirely in the overlayer material. That is, losses in the metal substrate were negligible.

Reaction at a platinum-gallium arsenide interface

Abstract The reaction at a Pt/n-GaAs interface as a result of annealing at 400°C was investigated. Both electron beam evaporated and electro-plated Pt films were studied. Optical reflection and transmission spectroscopy, secondary ion mass spectroscopy, X-ray diffractometry, scanning electron and ion microscopy, and X-ray energy spectroscopy were employed to examine the metal-semiconductor interface. An increase in the optical reflectivity was observed early in the annealing sequence. As has been observed by others, a complex layered structure formed at the interface, but the electron and ion micrographs revealed that gallium diffused rapidly through the platinum film at apparent imperfections in the Pt film. These imperfections were not visible in the micrographs prior to annealing and their nature has not been determined. These areas are believed to be primary sites for premature device failure. It appears that techniques such as SIMS which average over micron-sized or larger areas which indicate gallium diffusion to the Pt surface are correct, but may be misleading as to the mechanism.

Measurements of standing waves and the absorption coefficients of Various materials with surface electromagnetic waves on Al

The first measurements of the absorption coefficient of materials via surface electromagnetic wave (SEW) techniques are reported. By simply laying samples on a metal sheet on which SEW were passing, the transmittances and absorption coefficients of the sample have been determined. These measurements were made at microwave frequencies, but the general techniques are applicable over the entire frequency range from microwaves into the near ir. Solid samples were used in these measurements, but liquid or gases could also be studied by this new easy-to-use technique. Comments about the applicability of the technique to very thin samples are made. Another result reported is the existence of different propagating SEW modes as a function of the height of a sample (film thickness) measured from the metal-sample interface to the top of the sample at the sample-vacuum interface above.