Naftali Paul Eisenberg

Design of a diffractive optical element for wide spectral bandwidth.

A new method for eliminating the chromatic aberration of a diffractive optical element (DOE) for wideband wavelengths is presented. The wideband-wavelength diffractive optical element (WBDOE) consists of two aligned DOEs. The use of different dispersive materials for the two DOEs eliminates chromatic aberration. The design and simulation of a WBDOE for the visible spectrum are presented.

Design of diffractive optical elements for multiple wavelengths

A method for producing diffractive optical elements (DOEs) for multiple wavelengths without chromatic aberration is described. These DOEs can be designed for any distinct wavelength. The DOEs are produced from two different optical materials, taking advantage of their different refractive indices and dispersions.

Fabrication and testing of microlens arrays for the IR based on chalcogenide glassy resists

Abstract A new technique of microlens fabrication using inorganic chalcogenide photoresists is presented. High refractive index that is characteristic of chalcogenide photoresist films and correspondingly, the optical power of the microlenses, can be increased by means of silver photodoping of the ready-made microlens array. Unique properties of chalcogenide photoresists create new possibilities for the development of microoptical components for the IR. Microlens arrays on the base of AsS and AsSe photoresists were fabricated and tested.

PV module power gain due to bifacial design. Preliminary experimental and simulation data

Tests and subsequent simulation are needed for rational use of bifacial instead of traditional mono facial modules for generation of additional energy. Outdoor measurements of bifacial modules were undertaken at Jerusalem (∼32 deg. of North altitude). Method of determining nominal electrical parameters (Isc and Pmax) for each side of the module is proposed. The relationships of back module irradiance and Isc, Pmax generation are studied for different climatic and design conditions: diffusion/global ratio of sun illumination, seasonal sun position, module elevation above the mounting surface, tilt panel angle, and reflectance of the underlying surface. Non uniformity of back illumination and module elevation are among factors dramatically affecting the energy gain when using bifacial modules.

Dielectric microconcentrators for efficiency enhancement in concentrator solar cells

Metal fingers typically cover more than 10% of the active area of concentrator solar cells. Microfabricated dielectric optical designs that can completely eliminate front contact shading losses are explored. Essentially no microconcentrator optical losses need be incurred, series resistance losses can be reduced, and net efficiency gains of roughly 15% (relative) are realistic.

Photoalignment of Liquid Crystals on Chalcogenide Glassy Films

First observation of photoaligning of nematic liquid crystals (LC) on inorganic films, namely on a chalcogenide glassy films is reported. We found that irradiation of chalcogenide surfaces by visible laser beam of low-power (∼ 30 mW) results in efficient reorientation of the director in the irradiated areas. The anchoring energy associated with the light-induced easy orientation axis is of the order 10−6 J ∗ m−2 that is typical for standard organic polymer photoaligning materials. The surprise is that the direction of the reorientation depended on the time of the exposure. For short exposures director reoriented toward the polarization of light and longer exposures resulted in the reorientation away from the light polarization. The effect of light-induced alignment was used for recording of the surface-mediated electrically controlled holograms in the LC cell.

Wave-front control and aberration correction with a diffractive optical element.

A method that permits aberration correction and wave-front reshaping with a diffractive optical element (DOE) is described. Two aligned DOEs made of two different dispersive materials are used. The different dispersions of the two materials in addition to freedom in choosing their thicknesses enables the chromatic aberration and the wave fronts to be manipulated. Design and simulation of such DOEs are described.

Geometrical-transformation approach to optical two-dimensional beam shaping.

The use of geometrical transformations in the design of an optical beam shaper (OBS) is described. Elements based on this approach can transform light distributions into almost any arbitrary distribution. An example OBS is analyzed numerically.

Significance of bias light spectral composition for accurate measurement of silicon solar cell spectral response

To determine solar cell spectral response (SR) at working illumination conditions, measurements of the signal generated by a modulated spectral beam imposed on a DC short circuit current due to white light bias with different irradiances are typically used. In practice the bias light source does not usually simulate the suns spectrum. However the effect of the spectral composition of the bias light on the SR measurements is not known. The goal of this work is to find empirical evidence of the effect of the bias light spectrum on measured Si solar cell SR. The bifacial solar cell samples used for this study can be characterized by: significant dependence of SR on injection level, and different spatial distribution of bulk recombination centers. The sources of bias light were chosen based on their spectral composition which controls the depth distribution of carriers generation during SR measurements. An incandescent halogen lamp with a variable power supply voltage with/without optical neutral filters and ∼ 617 nm light emitting diodes were used. As the measurements show, the spectrum of the white bias light emitted by a tungsten filament of color temperature in the range 2400 – 3900 K is not a critical factor in SR measurements. However, use of highly absorbed bias light can result in a different SR compared to that measured with white light bias.

Fabrication of microlens array for the IR by lithographic processes using an inorganic chalcogenide photoresist

Micro-optical elements, particularly microlenses, are finding growing application in different fields of modern optoelectronics. One of the most promising methods of microlens fabrication is based on photolithographic processes. Organic photoresists were used in the earlier development of microlens arrays. A new technique of microlens fabrication using inorganic chalcogenide photoresists is presented. Such photoresists have many advantages, such as very high resolution, photosensitivity in wide spectral range, high values of refractive index, transparency in the IR range, and the ability to be used as positive or negative resists depending on the developer used. These unique properties create new possibilities for the development of microlens arrays in the IR.