Non-ideal Reflection Research Articles

Analysis and optimization of light outcoupling in OLEDs with external hierarchical textures.

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.

Wrinkling analysis for small solar-photon sails: An experimental and analytic approach for trajectory design

A good model of solar-radiation pressure induced thrust is one of the key points in sailcraft trajectory design. The sail membrane’s local topographic deformations, i.e. wrinkles and creases, are among the main aspects that such a model should include. We have analyzed the influence of wrinkles/creases, as a whole, by measuring the related deformations on small samples of sail membrane, 2.5 μm thick, consisting of CP1 and physical-vapor-deposition Aluminum. Experimental outcomes from our laboratory facility have been processed, statistically investigated, and inserted into the lightness vector formalism. We have used such formalism for accurate sailcraft trajectory computation via a non-ideal reflection sail thrust model. Finally, we computed the deviations of wrinkled-sail sailcraft final orbital states with respect to the no-wrinkle sail final orbital ones for a circular to circular 2D inward transfer. The radii of the orbits are 1 AU and the semi-major axis of Mercury, respectively. It appears that sail wrinkles and creases are no longer negligible in the sailcraft trajectory design.

Optical modeling of the emission zone profile and optimal emitter position based on the internal field profile of the air mode in organic light-emitting diodes.

We propose a theoretical formulation to calculate the internal profile of the air mode in the organic light-emitting diode (OLED) on the combination of the transfer matrix method and source-term method. The spatial distributions of the air mode are calculated in a top-emitting OLED with respect to the light polarization, extraction angle, dipole orientation, and dipole position. Air modes are also calculated on the basis of the previously used external source model, where the input optical wave is injected from the air into the OLED multilayer. Comparison of the calculated air modes between two models checks the validity of the external source model. In addition, we propose an improved formula to determine the optimal emitter positions that maximize the two-beam interference of the micro-cavity effect. In the improved formula, a non-ideal reflection phase shift at a reflective metal anode is treated as the skin depth of the air mode. Finally, the effect of the dipole orientation on the air mode is investigated. Compared with the air mode emitted by the horizontally oriented dipole, the air mode generated by the vertically oriented dipole has relatively small intensity and shows the opposite dependence of the emitter position variation. The calculation results of the internal profile of the air mode within the emission layer are matched with the profile of the emission zone obtained by output radiant flux on the basis of the currently used point dipole model.

Propagation of SHS Wave along a Wire in Conditions of Saved Radiant Losses

Propagation of solid flame over a combustible wire placed at the axis of cylindrical mirror was studied by mathematical modeling in 1D approximation. Wire radius was assumed small compared to mirror radius and width of the reaction zone. The radiative heat flux from a burned wire is partially transferred to the unburned part of the wire according to the reflection law. The use of cylindrical mirror was found to markedly extend the limits of combustion extinction in the system under investigation. Even in case of non-ideal reflection, the combustion temperature and burning velocity can be expected to attain superadiabatic values. The superadiabatic effect increased with increasing intensity of radiative flux and mirror reflectance.

Theoretical Analysis for Relations between Nonlinearity Errors and PBS in Heterodyne Interferometer

PBS is an important optical part of the heterodyne interferometer which separates the two orthogonal beams with the different frequencies from an incident mixed beam. The relations between the nonlinearity errors and the PBS in the heterodyne interferometer are studied in the paper. From the theoretical analysis, the nonlinearity errors don’t caused by the imperfect PBS with the nonideal transmission or the nonideal reflection, while the nonlinearity errors exists in the imperfect PBS with the nonideal transmission and the nonideal reflection. It’s a useful conclusion in the optical design of heterodyne interferometer.

Reduction of leakage effect with circulator-free fiber-gratings codec array in OCDMA network

The spectral-amplitude-coding (SAC) optical code-division multiple-access (OCDMA) systems use transmissive-mode fiber-Bragg gratings (FBG) instead of reflective-mode to avoid chip-timing. However, practical FBGs have non-ideal reflection coefficients to produce leakage effect and high phase-induced intensity noise (PIIN). This study is to cascade more of the same-frequency non-ideal FBGs to approach an ideal squared perfect spectrum for highly reliable network coding. A simple experiment is demonstrated to verify the square-like approach. Moreover, a residual-spectra eliminator (RSE) between FBG encoder and decoder is taken to remove non-coding part of the transmissive spectra for the suppression of PIIN in the receiver photo-detectors. Evaluation results show that the combination of RSE with cascaded FBGs can significantly improve the leakage and the PIIN effects for the SAC–OCDMA network.

Shock-wave compaction of the granular medium initiated by magnetically pulsed accelerated striker

The experimental and theoretical investigation of the granular medium shock-wave compaction process is made. The striker acceleration in the experiments is realized by pulsed magnetic field force action. The granular medium is alumina nanopowder. The mathematical model of the process describes the energy dissipation, which is stipulated by the work made to compact the powder, considering the loss for the non-ideal reflection of the shock wave from the discontinuity surfaces on the borders of the body being compacted. There is a satisfactory fit of the theoretical calculations and the final compact’s density experimental data. In terms of the low-energy shock front approximation the problem of the time dynamics calculation of the granular medium state is narrowed down to the system of ordinary non-linear differential equations. The limitation the striker to low energies linearizes the system, allowing to take its rigorous solution. The influence of such parameters as starting voltage of the capacitor, powder and striker masses and wave resistances of contacting materials on the compaction process is analyzed.

Dynamics of acoustoelectromagnetic solitons as a manifestation of higher nonlinearity

The acoustoelectromagnetic interaction is examined in a regime where three mechanisms must be taken into account simultaneously: photoelasticity, quadratic photoelasticity, and elastic nonlinearity. It is shown that beyond the critical conditions, acoustic solitary waves are formed at harmonic and subharmonic frequencies in a crystal. Including damping and nonideal reflection at the boundaries does not lead to the establishment of any sort of stationary state: a soliton spatial-temporal dynamic develops.

Theoretical analysis of an ultrasonic interferometer for precise measurements at high pressures

Expressions making it possible to calculate the transmission coefficient of an ultrasonic interferometer, its Q factor and errors of interferometric measurements are presented. These expressions are obtained on the basis of a one-dimensional model which takes into account the non-ideal reflection of acoustic waves from the transducers, diffraction losses and electromechanical properties of transducers. Fixed path ultrasonic interferometers which are widely used for high precision measurements of ultrasound absorption and velocity in liquids, include air-backed transducers. Air-backing limits the application of these interferometers for the measurements under the high pressures. The influence of non-gaseous backing of transducers on the characteristics of an interferometer is theoretically analysed by means of suggested expressions. Frequency dependences of main parameters of the interferometer are obtained. The possibility of high precision measurements of velocity and absorption of ultrasound in liquids under the high pressures by means of fixed path interferometers with liquid-backed transducers is shown.

Propagation of noise from multiple sources over level ground

Multiple noise sources on vehicles were simulated by two omnidirectional loudspeakers. They were used singly or in pairs to form monopoles, dipoles, or two correlated or uncorrelated sources. Pure tones, or 1/3-octave and octave-band noise at 1 KHz, were used. With fixed source height of 1.65 m and spacing from 0.5 to 3 m, noise levels were measured versus distance and azimuth over hard level ground with sparce vegetation. Noise Source Level was measured for pass-by at 50 ft. For microphone heights of 1.5-m fluctuations due to phase interference were observed for distance and angle measurements. However, for zero microphone height fluctuations versus distance were eliminated. Due to nonideal reflection from the ground spherical spreading was not observed out to the 100-ft limit of the measurements. A successful propagation model was derived using spherical spreading from each source and its image, and a reflection coefficient of one with a phase shift dependent on angle of incidence. [Work sponsored by U.S. Department of Transportation.]