Efficient Illumination Research Articles

Highly efficient tip-enhanced Raman spectroscopy and microscopy of strained silicon

We present a versatile tip-enhanced Raman spectroscopy (TERS) system that permits efficient illumination and detection of optical properties in the visible range to obtain high signal-to-noise Raman signals from surfaces and interfaces of materials using an edge filter. The cutoff wavelength of the edge filter is tuned by changing the angle of incident beam to deliver high incident power and effectively collect scattered near-field signals for nanoscopic investigation in depolarized TERS configuration. The dynamic design of the instrument provides a unique combination of features that allows us to perform reflection or transmission mode TERS to cover both opaque and transparent samples. A detailed description of improvements of TERS was carried out on a thin strained silicon surface layer. The utilization of an edge filter for shorter collection time, specialized tip for higher field enhancement and for elimination of Raman signal from the tip, shorter wavelength, sample orientation relative to probing polarization, and depolarized configuration for higher contrast Raman signal is discussed.

Two liquid crystal on silicon panel projector with efficient light-emitting diode illumination engine

LED-based projectors have numerous advantages compared to traditional projectors. They are more compact, they exhibit a larger color gamut and a longer lifetime, the supply voltage is lower and they can even operate on batteries. LEDs can switch rapidly (possibility to pulse) and they have a high dimming ratio (contrast considerations). However, they have low optical power per étendue, although this is also improving consistently. With an efficient illumination engine design we can build an LED projector with a moderate light output and with superior properties. We present a relatively compact LED projector with two liquid crystal on silicon (LCOS) light valves (LVs). One of these LVs alternately modulates red and blue information, while the other permanently modulates green information to achieve a good color balance. Additionally, we apply some methods to increase the brightness on the screen. Our two-LCOS approach results in a compact, efficient LED projector that produces 171 lm projected D65 flux.

DC Current-Induced Rollover of Illumination Efficiency of GaN-Based Power LEDs

Pulse drive currents were utilized to investigate dc current-induced rollover of illumination efficiency of GaN-based power light-emitting diodes (LEDs). By using the pulse drive currents, we can separate the effects that junction temperature and current injection have on dc current-induced rollover of illumination efficiency of GaN-based power LEDs. Comparing the measurement results obtained from pulse and dc drive currents, we verified that junction temperature and current injection were the major causes of dc current-induced rollover of illumination efficiency of power LEDs.

Solid-State Pressure-Tolerant Illumination for MBARI's Underwater Low-Light Imaging System

A significant amount of energy is consumed by the typical illumination systems of underwater vehicles. Attempts to utilize more efficient LED illumination underwater have been unsuccessful because the light-emitting diodes (LEDs) were coupled to a standard imaging system and they were not able to generate enough light to adequately illuminate the scene. In cases where the LEDs were grouped together, to provide more scene illumination, the lighting assembly was inefficient in size. The recent availability of high intensity LEDs provides a way to produce efficient and adequate lighting from a compact assembly. This paper covers the development of a deep ocean assembly based on these high intensity LEDs

14.1: Efficient and Compact Illumination in LED Projection Displays

AbstractIn this paper we propose an efficient illumination engine for LED based projection systems. Our design had to be both compact and efficient. We designed the projector with two LCOS light panels. We investigate two phenomena that affect the optical efficiency of this projector. We show that a relevant gain of the light output can be obtained by using certain methods.

Efficient Dual-Function Solar/Electric Light Guide to Enable Cost-Effective Core Daylighting

As a component of our cost-effective core daylighting research program, we have developed a hollow light guide that can be used to distribute sunlight collected by a heliostat device, and can also operate as an efficient fluorescent light fixture when the sunlight is insufficient to illuminate the workspace. This dual-function prism light guide structure has a cross-section that is similar to standard commercial fluorescent light fixtures, but with an increased depth in order to pipe the sunlight. The bottom surface of the guide is lined with a thin polycarbonate film having prismatic surface features, while the top and sides are lined with a highly-reflective multilayer optical film having a luminous reflectance greater than 98 percent. The angular constraints of the concentrated sunlight, combined with the high reflectance of the surfaces, enable the sunlight to be efficiently transported within the guide along a distance of greater than 10 m. The guide can also illuminate the room using electric sources, since the light from the lamps strikes the prismatic bottom surface at angles for which it is an efficient transmitter. Photometric characterization of the new dual-function guide has been performed, resulting in illuminance levels, uniformity and efficiency values well within recommended standards. The dual-function design approach has yielded a daylighting system that can be cost-effectively incorporated into standard office building construction.

Using a fly’s eye integrator in efficient illumination engines with multiple light-emitting diode light sources

High brightness light emitting diodes (LEDs) become a serious alternative for ultrahigh performance lamps in projection displays. We focus on the illumination part of a LED projection engine. We discuss the problem of using several LED light sources for each primary color. In critical applications, the use of several light sources for each color has important benefits. It increases the possible light output to the screen and makes it possible to design a system that is tolerant for failures of one of the LEDs. Therefore, we need an optical system that is both efficient and is able to produce a uniform light beam if one of the LEDs fails. We show that our illumination engine using a fly's eye integrator meets these requirements, using ray-tracing simulations of the engine. An efficient optimization method based on the simplex method [R. J. Koshel, Opt. Lett. 30, 649–651 (2005)] was developed to design the LED collimation reflective device with collection efficiencies up to 95%. The lens systems in the engine were designed with the same method. This results in a total system efficiency of 77%.

High Illumination Efficiency Linear Light Source Using Light Emitting Diodes

We propose a linear light source using light emitting diode (LED) and a light diffusion bar for linear illumination. In order to get high illumination efficiency, the following factors of the illumination system have been investigated: (1) the effect of the diffusion area, (2) the effect of the relative size of LED and the light diffusion bar. In conclusion, a bigger diffusion size will produce higher emitting efficiency, and a small relative size of emitting surface of LED and cross section of the light diffusion bar will also achieve higher emitting.

Illumination and annealing characteristics of two-dimensional electron gas systems in metal-organic vapor-phase epitaxy grown AlxGa1−xN∕AlN∕GaN heterostructures

We studied the persistent photoconductivity (PPC) effect in AlxGa1−xN∕AlN∕GaN heterostructures with two different Al compositions (x=0.15 and x=0.25). The two-dimensional electron gas formed at the AlN∕GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N∕AlN∕GaN sample from 1.6×1012to5.9×1012cm−2, while the electron mobility was enhanced from 9540to21400cm2∕Vs at T=1.6K. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength, being highest close to the band gap and decreasing at longer wavelengths. The PPC effect became fairly weak for illumination wavelengths longer than ∼530nm and showed a more complex response with an initial negative photoconductivity in the infrared region of the spectrum (λ>700nm). The maximum PPC efficiency for 390nm illumination was 0.011% and 0.005% for Al0.25Ga0.75N∕AlN∕GaN and Al0.15Ga0.85N∕AlN∕GaN samples, respectively. After illumination, the carrier density could be reduced by annealing the sample. Annealing characteristics of the PPC effect were studied in the 20–280K temperature range. We found that annealing at 280K was not sufficient for full recovery of the carrier density. In fact, the PPC effect occurs in these samples even at room temperature. Comparing the measurement results of two samples, the Al0.25Ga0.75N∕AlN∕GaN sample had a larger response to illumination and displayed a smaller recovery with thermal annealing. This result suggests that the energy scales of the defect configuration-coordinate diagrams for these samples are different, depending on their Al composition.

Improving the illumination efficiency and color temperature for a projection system by depositing thin-film coatings on an x-cube prism

A new x-cube prism with small polarizing dichroic filters was made for an optical projection system. The x-cube prism was used to combine the three primary colors, which were divided by the preset dichroic mirrors. A coating was designed and fabricated such that s- and p-polarized light was shifted to be obliquely incident in the x-cube prism: the shift was the same as that at the dividing dichroic mirrors. Hence, energy loss was lower than that associated with the conventional x-cube prism, and the brightness of the projection system was 33.2% higher and the color temperature was 18.2% higher than those of the conventional x-cube prism.

White LED Based Illumination Systems for Indian Villages

This paper discusses the need for and benefits from energy efficient illumination systems for rural Indian homes. The role of White LEDs in providing such illumination systems is discussed. About two billion people in remote areas of developing nations have no electric lighting, a commodity industrialized nations take for granted. Poor lighting in homes hinders children's learning, affects family health, and limits opportunities for a better life. White light-emitting diodes supply enough light for a child to read by. This simple but revolutionary technology can be supplied to homes. This technology can light an entire rural village with less energy than that used by a single, conventional, 100-watt incandescent lamp.

Light-emitting diode illumination design with a condensing sphere

An illumination system is described that comprises a glass or plastic sphere, an embedded light-emitting diode (LED) source, and a reflecting or scattering mirror. The rays from the LED are either refracted in the forward direction or totally internally reflected by the sphere. The mirror breaks the total internal reflection and thus sends the rays in the forward direction. The illumination pattern and efficiency of the system are analyzed. This system is extremely compact and efficient and is a good starting point for a complex illumination system design.

Focusing characteristics of optical fiber axicon microlens for near-field spectroscopy: Dependence of tip apex angle

We fabricated axicon microlenses on a single-mode bare optical fiber by using selective chemical etching technique. By varying the concentration and mixture ratios of etching solutions, we could make axicon microlenses with different apex angles (118°, 107° and 90°). We measured the illumination and collection efficiency of these microlenses by both objective-lens imaging and near-field photoluminescence (PL) spectroscopy of semiconductor quantum dots with respect to the distance between the sample and the axicon lens probe. We found that axicons with 118° and 107° [90°] apex angle tend to exhibit the laser focusing spot sizes of about 406 and 478nm [382nm] and maintain the high [slightly low] collection PL intensity with the distance between the sample and the axicon probe.

Cathodic deposition of CdSe films from dimethyl formamide solution at optimized temperature

In the present paper, thin film CdSe compound semiconductors have been electroplated on transparent conducting oxide coated glass substrates from nonaqueous dimethyl formamide bath containing CdCl2, KI and Se under controlled temperature ranging from 100 to 140°C. Thickness of the deposited films as obtained through focussed ion beam technique as well as their microstructural and photoelectrochemical properties have been found to depend on temperature. The film growth was therefore optimized at a bath temperature ∼125°C. The formation of crystallites in the range of 100–150nm size has been ascertained through atomic force microscopy and scanning electron microscopy. Energy dispersive analysis of X-rays for the as deposited film confirmed the 1:1 composition of CdSe compound in the matrix exhibiting band-gap energy of 1.74eV. Microstructural properties of the deposited films have been determined through X-ray diffraction studies, high-resolution transmission electron microscopy and electron diffraction pattern analysis. Electrochemical impedance spectroscopy and current-potential measurements have been performed to characterize the electrochemical behavior of the semiconductor–electrolyte interface. The photo-activity of the films have been recorded in polysulphide solution under illumination and solar conversion efficiency ≥1% was achieved.

An efficient illumination normalization method for face recognition

In this paper, an efficient representation method insensitive to varying illumination is proposed for human face recognition. Theoretical analysis based on the human face model and the illumination model shows that the effects of varying lighting on a human face image can be modeled by a sequence of multiplicative and additive noises. Instead of computing these noises, which is very difficult for real applications, we aim to reduce or even remove their effect. In our method, a local normalization technique is applied to an image, which can effectively and efficiently eliminate the effect of uneven illuminations while keeping the local statistical properties of the processed image the same as in the corresponding image under normal lighting condition. After processing, the image under varying illumination will have similar pixel values to the corresponding image that is under normal lighting condition. Then, the processed images are used for face recognition. The proposed algorithm has been evaluated based on the Yale database, the AR database, the PIE database, the YaleB database and the combined database by using different face recognition methods such as PCA, ICA and Gabor wavelets. Consistent and promising results were obtained, which show that our method can effectively eliminate the effect of uneven illumination and greatly improve the recognition results.

Accretion of helium and metal-rich gas onto neutron stars and black holes at high luminosities

Ultraluminous X-ray sources fed by Wolf-Rayet star winds and X-ray bursters in ultracompact binaries with He or C white dwarfs have accretion disks, whose properties may significantly differ from those of pure H alpha-accretion disks. We have therefore included the dependence on charge number Z and mean molecular weights mu_{e/I} into the Shakura and Sunyaev (1973) scaling relations for the key parameters of the disk. Furthermore, we also consider the case of the pseudo-Newtonian potential of Paczynsky and Wiita (1980). These scaling relations might become useful, e.g., when estimating the illumination efficiency of the external parts of the disk. We also address the changes in the structure of the boundary (spreading) layer on the surface of neutron stars, occurring in the case of H depleted accretion disks.

Differences in the structure composition of microcrystalline silicon solar cells deposited by HWCVD and PECVD: Influence on open circuit voltage

Structural properties, current–voltage ( J– V) characteristics in the dark and under illumination and quantum efficiency are systematically studied and compared for μc-Si:H solar cells with i-layers deposited by HWCVD or PECVD. A correlation between the increasing V OC and decreasing crystalline volume fraction of the i-layer can be observed in solar cells deposited by HWCVD and PECVD. At high crystallinity, similar J– V parameters are obtained for both methods. However, HWCVD solar cells can be prepared with lower crystalline volume fractions below 50%, without the drastic drop of solar performance observed in PECVD solar cells.

Uniform illumination of optically dense NMR samples

We demonstrate a simple, inexpensive method for in situ laser illumination of NMR samples using a stepwise tapered optical fibre to deliver light uniformly along the axis of a 5 mm NMR tube. The optical path length of the incident light inside the sample is about 3 mm, allowing efficient illumination of optically dense samples. The degradation in spectral resolution and the reduction in filling factor are both minimal. Probe modifications are not required.

Ar 가스 압력과 RF 전력에 따른 유도결합형 플라즈마의 전기적 및 광학적 특성

In this paper, the electrical and emission properties of electrodeless fluorescent lamp were discussed using the inductively coupled plasma (ICP) with the variation of argon gas pressure and RF power. The RF output was applied to the antenna in the range of 5∼50 W at 13.56 MHz. The internal plasma voltage of the chamber and the probe current were measured while varying the supply voltage to the Langmuir probe in the range of －100V∼＋100V. When the pressure of argon gas was increased, electric current was decreased. There was a significant electric current increase from 10 to 30 W. Also, when the RF power was increased, electron density was increased. Also, the emission spectrum, Ar- I lins, luminance were investigated. At this time, the input parameter for ICP RF plasma, Ar gas pressure and RF power were applied in the range of 10∼60 mTorr, 10∼300 W, respectively. This implies that this method can be used to find an optimal RF power for efficient light illumination in an electrodeless fluorescent lamp.

Output Characteristics of Solar-Power-Driven Thermionic Energy Converter

A solar-power-driven thermionic energy converter abbreviated as Solar TEC is operated by illumination of solar light condensed by a large-scale Fresnel lens 105 cm in length and 70 cm in width. It was found that an output current takes large peaks at the lower emitter temperature because the emitter work function closely related to the thermionic electron emission decreases at a constant cesium pressure with decreasing emitter temperature. The maximum short circuit current was 0.73 A at 62 s after the onset of the illumination throughout the experiment for 500 s, where the solar power density on the ground was approximately 800 W/m2. The barrier index also took a minimum value of 2.3 eV at the same time. To increase the output characteristics of the Solar TEC, the emitter and cesium temperatures should be increased along the curve of β=1, where β denotes the space charge neutrality. It was found that the emitter with a light trap is effective in improving the energy conversion efficiency of the Solar TEC, since it realizes high absorptivity and low emissivity at once, which causes the emitter to have high thermal efficiency for solar power illumination.