Wide-angle Interference Research Articles

Effect of supersaturation on structural stress of rapidly growing KDP crystals studied by wide-angle conoscopic interference

Photoelastic effect was applied to analyze the relationship between fringe spacing in wide-angle conoscopic interference and structural stress of KDP crystals.

Broadband responsivity enhancement of Si photodiodes by a plasmonic antireflection bilayer.

Randomly distributed plasmonic Ag nanoparticles (NPs) with various sizes were fabricated by a reflow process to an island-shaped Ag thin-film deposited on a Si photodiode. These NPs conformally enclosed by an antireflective (AR)-type SiNx/SiO2 bilayer reveal significantly diminished reflectance in a broad wavelength (500 nm - 1100 nm) as compared to the cases of Ag NPs or SiO2 layer enclosing Ag NPs on the Si substrate. Accordingly, the forward scattering and the total reflection along with wide-angle interference in between the dielectric bilayer incorporating the Ag NPs induce highly increased light absorption in the Si substrate. The fabricated Si photodiode adopting the plasmonic AR bilayer shows the responsivity peak value of 0.72 A/W at 835 nm wavelength and significant responsivity enhancement up to 40% relative to a bare Si photodiode in a wavelength range of 500 nm to 1000 nm.

Enhanced Electrical and Thermal Performance of Wet-Laid Based Graphite-Laminated Carbon Non-woven Composite

This study presents the facile synthesis of an electrically conductive carbon-based non-woven composite using a wet-laid bonding process. A highly stable composite of graphite nanoplatelets (GnPs) was attached to the non-woven fabric to be used for thermal and electrical applications. The GnPs were coated through lamination or attached using a modified wet-laid method. Different carbon fibre and graphite nanoplatelets and their composites were prepared. Their properties were investigated using field emission-scanning electron microscopy, wide-angle x-ray diffraction, Raman spectroscopy, electrochemical, thermal, and electromagnetic interference shielding analyser. The laminated structure showed a very high electrical conductivity of 13,960.5 S/m, thermal distribution of 30.11 mm2/s, and electromagnetic interference shielding efficiency of more than 99.99%. The prepared composite also showed good flexibility and the potential for use in wearable devices. Thus, it can be said that this highly functional composite non-woven design provides a foundation for the development of more functional applications in e-textiles as next generation electrical devices.

A Hybrid Electric and Thermal Solar Receiver

Summary Solar energy offers a promising renewable energy source; however, it is expensive to store electricity from photovoltaics (PV), the most widely deployed solar electricity technology. Solar thermal energy technologies can be paired with inexpensive thermal storage, but are more expensive overall. We have developed a solar receiver that combines PV and solar thermal systems to efficiently convert solar radiation to electricity (to be used immediately) and thermal energy (to be stored and converted to electricity on demand). This paper describes the Hybrid Electric And Thermal Solar (HEATS) receiver and models its performance. An idealized model predicts high solar-to-electricity efficiency (35.2%) with high dispatchability (44.2% of electricity from thermal energy) at an operating temperature of 775 K. Modeling using measured performance values for HEATS subcomponents predicts 26.8% efficiency and 81% dispatchability with silicon PV and 28.5% efficiency and 76% dispatchability with gallium arsenide PV, both operating at 700 K.

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the use of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.

Pure and Stable Top-Emitting White Organic Light-Emitting Diodes Utilizing Heterojunction Blue Emission Layers and Wide-Angle Interference

In top-emitting white organic light-emitting diodes (TWOLEDs), it is usually difficult to realize a good chromaticity due to the strong suppression on the blue emission induced by the microcavity effect. In our work, the blue emission layer (EML) is located near the hole transport layer and the reflective anode to strengthen the wide-angle interference on the blue emission and enhance the output of light. Then we utilize the dual blue EMLs based on an electron-rich heterojunction to constrain most of the excitons in the blue EMLs. With the above two strategies, the intensity of the blue emission is significantly enhanced accompanying the chromaticity improvement in white emission. Some key factors including exciton distribution, energy transfer, and carrier trapping are analyzed to design the structure of the EMLs to acquire the pure and stable white emission. The excellent color stability with a Commission International de L'Eclairage (CIE) coordinate drift of only (0.009, 0.001) in the luminance range of 10-10(4) cd/m(2) is obtained in our optimized TWOLED. The TWOLED also shows the high performances with a maximum luminance of 15360 cd/m(2), the CIE coordinates of (0.33, 0.41), and a current efficiency of 13.3 cd/A.

Top-emitting white organic light-emitting diodes based on a ZnS light outcoupling layer

Top-emitting white organic light-emitting diode (TEWOLED) has potential applications in lighting and full color displays. Microcavity effect in TEWOLED restrains the realization of the white emission with excellent optical and electric performances. In this paper, a ZnS film with a high refractive index used as a light outcoupling layer is introduced into the metal cathode to enhance its transmittivity to a maximal value in the blue light wavelength region. In addition, transfer matrix theory is utilized to optimize the thicknesses of the cathode and the ZnS outcoupling layer and the wide-angle interference is used to design the position of the blue emission layer inside the organic light-emitting diode. Based on the above work, the white light with relatively high luminous efficiency, good color purity, and small CIE coordinate change is acquired. The corresponding luminance and current efficicency are 9213 cd/m2 and 3 cd/A, respectively. The CIE coordinates belong to the white emission and are near the white light equal-energy point. The white emission also shows stable spectra with respect to the observation angle, with a limited CIE coordinate change of (0.02, 0) for a large observation angle change from 0 to 60.

利用有机覆盖层提高OLED出光效率

A bottom emitting organic light-emitting devices was fabricated by depositing Alq as capping layer to the glass substrate.The device structure were Glass/Alq(x nm)/Al(15 nm)/MoO3(30 nm)/ NPB(60 nm)/Alq(65 nm)/LiF(1 nm)/Al(150 nm).By studying the radiation characteristics of the devices,it was found that the variation of the EL emission due to the capping layer can be entirely accounted for a change in optical interference effects.The complex interplay between wide-angle and multiple-beam interference can be controlled via the optical thickness of the dielectric capping layer on top of the cathode.Semitransparent Al film was anode.The capping layer deposited to the glass substrate formed microcavity devices with cathode.By changing the thickness of capping layer to adjust the microcavity length,the center wavelength EL spectra of OLED was red-shifted.

Blue top-emitting organic light-emitting devices based on wide-angle interference enhancement and suppression of multiple-beam interference

Blue top-emitting organic light-emitting devices (TEOLEDs) based on blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C 2′] picolinate (FIrpic) are demonstrated. Instead of using microcavity effects to obtain the blue top emission in conventional reports, the blue emission with a good chromaticity is achieved in this paper through the suppression of the multiple-beam interference by introducing a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline light outcoupling layer onto the semitransparent Sm/Ag cathode. The electroluminescent performances of the blue emission is further improved based on the effective carrier transport and the consideration of the wide-angle interference at the emission peak of FIrpic with a maximum luminance of 8029 cd/m 2 and a luminous efficiency of 4.02 cd/A achieved at 14 V and 10 V, respectively. With a polarizer on the top cathode, a high pixel contrast ratio of 113:1 is realized under an ambient illumination of 140 lx and a pixel brightness of 1000 cd/m 2.

The effects of planar metallic interfaces on the radiation of nearby electrical dipoles

Light emission by excited species that decay via an electrical dipole transition ismodeled as an electrical dipole antenna. We examine the various effects thatoccur when such a dipole is close to a metallic interface: wide-angle interference,coupling to the surface plasmon mode and absorption of the near-field. Analyticalexpressions for the power coupled to the surface plasmon and near-field absorption arederived. The case of a non-absorbing metal is compared to that of an absorbingmetal.

Blue top-emitting organic light-emitting devices using a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline outcoupling layer

We fabricate a blue top-emitting organic light-emitting device (TEOLED) based on 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl. Different from the conventional TEOLEDs that use ITO as a thickness adjustment layer to make the cavity length matchable with the resonant wavelength of the blue light, we construct the blue emission TEOLED through suppressing multiple-beam interference and utilizing wide-angle interference to enhance the blue emission. With a 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline light outcoupling layer to reduce the reflectivity of the Sm/Ag cathode, the blue emission can be obtained and its chromaticity is comparative to that from a bottom-emitting OLED. In addition, the blue emission shows stable spectra when the viewing angle alters from 0° to 75°.

The design of broadband, wide-angle interference filters for solar concentrating systems

The optical performance of spectrally selective interference filters for wide-angle solar applications is addressed. A radially variable interference filter is proposed that can maintain acceptable efficiency over its entire surface in solar concentrating systems with a wide field of view. By applying ray tracing methods and a mapping technique, the angle at which the greatest proportion of energy is incident can be determined at as a function of position on the filter surface. The resulting angular distribution is used to design the interference filter with a tapered thickness profile for optimum performance according to the changing mean angle. The method has been applied for the optimisation of a spectral beam splitter in a hybrid photovoltaic/thermal central receiver system. Two types of interference filters are compared: the discrete multilayer and the rugate filter. Results for bandpass and bandstop configurations are presented, and the performance and practical issues associated with each solution are discussed.

Investigation of the spectra of phosphorescent organic light-emitting devices in relation to emission zone

The dependence of the electroluminescent spectra on the emission zone of blue electrophosphorscent light emitting diodes (PHOLEDs) was investigated. The light emission of a PHOLED was tuned from blue to greenish blue by adjusting the position of the emission zone in the PHOLED. Experimental results agreed well with the numerical simulation based on the effect of the wide-angle optical interference by the metal cathode. The comparison of the numerical results and the electroluminescent spectra of the PHOLED was then extended to serve as the basis of another method to determine the location of the emission zones of PHOLEDs.

Tuning the emission characteristics of top-emitting organic light-emitting devices by means of a dielectric capping layer: An experimental and theoretical study

The emission characteristics of top-emitting organic light-emitting devices (OLEDs) have been studied experimentally and theoretically to derive a quantitative understanding of the effect of a dielectric capping layer. We demonstrated that the angular intensity distribution and the spectral characteristics can be tuned and the light outcoupling enhanced simply by varying the optical thickness of a dielectric layer deposited on top of a semitransparent metal electrode. With the capping-layer concept, the outcoupled light intensity in forward direction was increased by a factor of 1.7, and concomitantly a high color purity achieved. An optical model based on a classical approach was used to calculate the emission characteristics. The excellent agreement between measured and simulated data shows that the capping layer controls the interplay between different interference effects such as wide-angle and multiple-beam interference occurring in top-emitting OLEDs. The strength of the capping layer concept is in particular that the optical and the electrical device performance can be optimized separately.

KOPSKO: a Computer Program for Generation of Kossel and Pseudo Kossel Diffraction Patterns

Diffraction techniques are widely used especially as additional tools for analytical microprobe analysis. A supplementary device to a scanning electron microscope (SEM) allows taking of X-ray lattice source and wide angle interference patterns, now termed Kossel and Pseudo Kossel patterns, respectively, in transmission and back reflection arrangement as reported by DABRITZ et al. (1986, 1997a,b). The developed program KOPSKO simulates exactly the entire reflection system of Kossel and Pseudo Kossel diffraction patterns basing on the geometric diffraction theory. It permits phase, orientation, and structure determination. The present paper shows the wide range of possibilities using the computerized analysis in this field. Initially it deals with simulation of Kossel patterns, which are excellent suitable for a precise determination of lattice constants in the micro range for instance. A new way for simulation of Pseudo Kossel diffraction patterns using three dimensional vector algebra to calculate reflections in point by point procedure is presented in the second part. The attained precise coincidence of simulation and experimentally taken Pseudo Kossel patterns allows a relatively easy determination of crystallographic data of mono- and polycrystals. Particularly the program is designed to determine lattice constants precisely, for the complex divergent beam X-ray interferences, too. Through the three dimensional simulation it takes into account shade originated by the target holder. Moreover, the three dimensional point by point procedure enables the localization of lattice imperfections as well as the consideration of grain size effects in polycrystals. which lead to interruptions of Pseudo Kossel lines. By simulation of diffraction patterns of polycrystalline materials the study of such specimens is essentially simplified.

Interference effects in bilayer organic light-emitting diodes

The electroluminescent spectra and the light intensities of Alq3-based organic light-emitting diodes were measured as a function of the thickness of the light-emitting layer. A maximum in the light intensity occurs when the thickness of this layer is approximately 600 Å, whereas a minimum in the light intensity occurs at about 1400 Å. The electroluminescent spectra were also found to vary strongly with the thickness of the light-emitting layer. Computer simulation, based on wide-angle interference of light-emitting dipoles from a reflective mirror, can account for the experimental observations.

Study on optical efficiency of alternating-current thin-film electroluminescent devices

An expression of the optical efficiency for alternating current thin film electroluminescent (ACTFEL) devices is given by a model of an optical microscopic cavity, and the optimization of the structure of the ACTFEL device is discussed. The model is reasonable since the radiation patterns developed by it coincide with the experimental results. The model indicates that in the ACTFEL device, the wide-angle interference is obvious, but the multiple-beam interference is slight.

Wide-angle interference and cavity effects in thin ZnS layers doped with Mn

Wide-angle interference and cavity effects in thin ZnS layers doped with Mn

Radiation patterns from lens-coupled terahertz antennas

We report on investigations of the angular distribution of the radiation emitted from a terahertz antenna system equipped with a truncated spherical silicon lens. The pattern is calculated by wide-angle interference principles and Huygens-Fresnel diffraction theory. Experimental determination of the radiation pattern is performed by spatially resolved terahertz time-domain spectroscopy. Good agreement between theory and experiment is obtained, and we find that the terahertz beam can be represented by a Gaussian beam emitted from a circular aperture equal to the diameter of the lens.

Wide angle interference of coherently scattered light

A classical experiment, which can easily be performed in the classroom is reported here showing that light scattered in all directions is coherent whereas the usual interferometers offer interference within a restricted spatial angle only. The historical background of this experiment is given together with a brief survey of the early experiments and experimentators among whom is Schrodinger.