High Transmission Coefficient Research Articles

Pulsed laser-induced desorption and optical imaging on a nanometer scale with scanning near-field microscopy using chemically etched fiber tips

Laser-induced desorption on a nanometer scale using scanning near-field optical microscopy (SNOM) is demonstrated. Pulsed laser-induced desorption of anthracene with completely metallized SNOM fiber tips resulted in a lateral resolution of 70 nm. This became possible due to the use of chemically etched tips with a taper region smaller than 200 μm and cone angles varying from 6 to 30 degrees. These tips are further useful for optical imaging with a very high optical transmission coefficient (up to 10−3), achieving a lateral resolution of 80 nm.

DC conductivity in polycrystalline metals for bulk and thin-film samples

A new description of the DC conductivity in polycrystalline bulk metal and thin metal films is proposed in which isotropic background scattering and scattering due to grain boundaries are considered simultaneously. The general formula for the relaxation time for partly diffuse and partly specular scattering grain boundaries is obtained. The well known Mayadas and Shatzkes and Pichard-Tellier and Tosser models represent special cases of the author's description. For appropriately high specular reflection and small transmission coefficients of electrons through the grain boundaries a negative value of the temperature coefficient of the resistivity is obtained.

High-efficiency combined laser and photodetector in a monolithic integrated-optics module utilizing coupled waveguides

An integrated structure was made containing a laser and a photodetector, with a high transmission coefficient of the optical power, in a monolithic module utilizing an AlGaAs/GaAs heterostructure forming a system of coupled waveguides. Efficient operation of the laser having a broad contact was achieved by the presence, within its active part of regions of alternating length. Variation of the lengths of the elements of a line of slots with vertical walls, used as a resonator mirror, made it possible to vary the coefficient of coupling between the laser and the photodetector from practically 0 to 100%.

In vitro Depth of Cure of Photo-activated Composites

The in vitro depth of cure of six photo-activated composites was studied by measurement of hardness, transverse strength, and light transmission coefficients. Both Barcol hardness and transverse strength were sensitive techniques for characterizing depth of cure. As a group, the visible light-activated composites had higher values of depth of cure and higher transmission coefficients than did the ultraviolet light-activated composites.

Experimental investigation of noise immunity in noncoherent spatially separated reception of optical signals in the atmosphere

An experimental investigation was made of the noise immunity in noncoherent spatially separated reception of optical signals in a turbulent atmosphere over a 500 m long slightly inclined path. A comparative analysis was made between the noise immunity of various methods of combining signals from separate channels when using spatially separated reception, namely: discrete (majority) summation, automatic selection of the channel with the highest transmission coefficient, and coherent (linear) summation in the case of noncoherent reception. The probability distribution laws of the received signals were studied for these methods of combining the channels. Measurements were made of the error reception probability as a function of the signal-to-noise ratio and degree of atmospheric turbulence, and the results were compared with theoretical estimates.

Structure and interface oxidation state of ZnO r.f. sputtered onto silicon and SiO 2/Si

The crystallographic structure and interface oxidation state of thin ZnO films r.f. sputtered onto silicon and SiO 2/Si substrates were investigated. The quality of the ZnO layers is characterized by a high optical transmission coefficient which is close to unity up to an optical band gap corresponding to that of single-crystal ZnO. The values of the transmission coefficients and band edge provide sensitive indicators of film quality. The deposited layers have a wurtzite crystal structure with lattice parameters a 0 = 3.24±0.01 A ̊ and c 0 = 5.23±0.01 A ̊ , corresponding closely with bulk ZnO. The orientation of the ZnO grains with respect to the substrate depends critically on the interface oxidation state. An analysis of X-ray photoelectron spectra provides an assessment of this interface oxidation state.

Electrochemical Patterning of Tin Oxide Films

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Effects of Different Flow Field Conditions on the High Power Transmission Properties of a Reentry Plasma

A computer program for calculating the high power microwave transmission coefficients of a chemically seeded reentry plasma has been described in two previous reports. It has been explained how the computer code can be used to optimize the amount of high power that can be transmitted from a reentry vehicle. Using a half implicit – half explicit time integration scheme, the electron and ion transport equations coupled with Maxwell's equations are numerically integrated to determine the nonlinear reflection and transmission coefficients of a reentry plasma. Graphs are presented of the electron density profile and plane wave reflection and transmission coefficients corresponding to the flow field conditions of a blunt-nosed reentry vehicle. The nonlinear transmission effects are studied as a function of vehicle altitude, antenna location on the vehicle, incident power level, pulse length, pulse repetition frequency, and convective flow velocity. Good agreement is obtained between theoretical results and actual rocket flight data.