Lau array illuminator

Spatial coherence can be created by appropriate spatial arrangements of incoherent point sources. Lau used a source of extended light and two amplitude gratings of identical periods, separated by the quarter Talbot distance, to provide coherent light. Because of the two successive amplitude gratings, most of the power is lost. By modifying the geometry of the second grating, I designed an array illuminator, providing several compression ratios and various topologies of the output plane, with significantly reduced losses. To further improve the power efficiency of the system, I used a longitudinal mirror system to collect the light rays that are lost in the initial Lau setup. Both one- and two-dimensional geometries are considered.     

Array illuminator with arbitrary fan-out

An approach for designing Talbot array illuminators that produce quasi-arbitrary numbers of spots and quasi-arbitrary distributions of these spots in the output plane is proposed. The approach consists in combining elementary Talbot array illuminators. In addition to the quasi-arbitrary topology of the output spots, the resulting compound array illuminator shows several advantages such as its ability to be used for both coherent and incoherent imaging. Compared with elementary array illuminators, the compound illuminator does not add any specific technological complication.     

Compact red-green-blue beam illuminator and expander

A compact multicolor beam illuminator and a compact multicolor beam expander are presented. The illuminator performs the dual task of demultiplexing a narrow red-green-blue (RGB) input beam into three separate beams, each of a different color, and expanding them to yield three separate magnified plane waves. The beam expander expands a narrow RGB input beam into a single magnified RGB plane wave. The design and recording procedures, along with experimental results for a beam illuminator and a beam expander with a magnification of approximately 3, are presented.     

Real-time precision refractometry: new approaches

We introduce two new approaches for near-real-time, high-precision tracking of the refractive index of the ambient atmosphere. The methods can be realized at low cost and are expected to have important practical application in those accurate dimensional metrology applications employing interferometry in air. A valuable potential application is the control of step-and-repeat mask positioning for integrated circuit production in which temporal stability time scales over days can be crucial. Extension of the methods to absolute index measurement is discussed.     

Liquid refractometry by the rainbow method

A new method for measuring the refractive index of liquid, proposed in a previous paper [Appl. Opt. 36, 5552-5556 (1997)], has been developed. The minimum deviation of a laser beam deflected by a liquid-filled cylindrical cell was calculated by use of geometric optics. These theoretical results were compared with experimental results, with excellent agreement. As a result, the unknown refractive index of a liquid could be obtained by use of a computer calculation to give a best fit. The computer calculation showed that the sensitivity of the refractometer increases with the cell-wall thickness until total reflection takes place. A small refractive-index difference can be detected within a precision of 1 x 10(-6) by use of a metal-oxide semiconductor linear image sensor. We show how to calibrate the refractometer with pure water at 3.98 degrees C.     

Balance-type interference system for isolated-liquid refractometry

Translated from Izmeritel'naya Tekhnika, No. 4, pp. 16–18, April, 1993.     

Interferometric array illuminator with analysis of nonobservable fringes

Interferometric methods for array generation offer various advantages over diffractive methods. Use of polarizing elements in an interferometric array illuminator results in interesting properties in addition to improving the efficiency considerably from low levels. The array pattern appears as nonobservable fringes that can be observed only with a polarizer, and the interferometer is insensitive to one of the tilt components. A thorough analysis of such an interferometric array illuminator is presented in this paper. Several possible applications of such an interferometer in addition to use as an array illuminator are proposed.     

Optical characterization of polyethylene films by refractometry

Refractometrical measurements of polyethylene films have been obtained using a modified Abbe's refractometer that includes polarized and monochromatic light. The ordinary and extraordinary refractive index values have been obtained considering an anisotropic uniaxic model. These values are analysed in relation to the previously known degree of crystallinity in the samples of this material. The specular reflectance is derived from the Fresnel formulae and an evaluation of diffused reflectance has been made. We find that the diffuse reflectance values increase with average roughness of the polyethylene films. This question is of particular interest for the surface characterization of these materials.     

High throughput reflective light guide for planar illuminator

A light guide fully composed of reflective plate has been proposed for a planar illuminator with the light source located at the side edge. Using mirror reflection as the light guiding mechanism increases the light acceptance angle of the light guide, and the hollow structure allows increasing the source coupling area without inducing further weight. Accompanying with the optical films, for example, a diffuser, a prismatic film, and a reflective polarizer to spread light distribution, the uniformity of the prototype has shown the feasibility for a planar illuminator.     

Fourier-synthesis custom-coherence illuminator for extreme ultraviolet microfield lithography

Scanning illumination systems provide for a powerful and flexible means for controlling illumination coherence properties. Here we present a scanning Fourier synthesis illuminator that enables microfield extreme ultraviolet lithography to be performed on an intrinsically coherent synchrotron undulator beamline. The effectiveness of the system is demonstrated through a variety of print experiments, including the use of resolution enhancing coherence functions that enable the printing of 50-nm line-space features by use of a lithographic optic with a numerical aperture of 0.1 and an operational wavelength of 13.4 nm.     

Number of phase levels in a two-dimensional separable Talbot array illuminator

The number of phase levels in a Talbot array illuminator (TAIL) is an important factor for estimation of practical fabrication complexity and cost. We show that the number of phase levels in a two-dimensional TAIL (2D-TAIL) has a simple relation to the prime number. When the output array is alternatively pi phase modulated, there are similar simple relations. These simple relations should be highly interesting for practical use. An experiment with the 2D-TAIL based on the joint-Talbot effect is given as well.     

Number of phase levels of a talbot array illuminator

The number of phase levels of a Talbot array illuminator is an important factor in the estimation of practical fabrication complexity and cost. We show that the number (L) of phase levels of a Talbot array illuminator has a simple relationship to the prime number. When there is an alternative pi-phase modulation in the output array, the relations are similar.     

Simulation study on refractometry by the rainbow method

To realize a high-precision refractive-index measurement by the rainbow method by use of multifringes, the characteristics of several orders of supernumerary bow fringes are made clear by a simulation based on the Huygens-Fresnel principle. The fringe intervals computed are precisely coincident with those obtained in experiments. As a result a suitable combination of the diameter of the cylinder containing the sample and the beam size of the laser has been determined. By use of the characteristic curve of the deviation angle versus the refractive index for each fringe and by the statistical treatment, measurement with high precision was demonstrated.     

Features of the refractometry of turbulent gas flows

The features of the interference refractometry of turbulent gas flows, which are a special case of a randomly inhomogeneous medium, are considered. Recommendations are made on the quasi-optimal choice of the parameters of the refractometer system. Translated from Izmeritel’naya Tekhnika, No. 8, pp. 31–35, August, 1996.     

A VUV prism spectrometer for RICH radiator refractometry

Abstract

A prism spectrometer has been developed to operate in the VUV wavelength range from 120 to 200 nm. It can be used as a pre-disperser in conjunction with a Fabry-Perot based gas refractometer. This instrument has also been used to measure the refractive index of the liquid radiator C₆F₁₄ in various spectral lines. This radiator is used in the RICH detectors of the DELPHI experiment and has been proposed for ALICE, and LHCb experiments. The spectral resolution of the system is improved as the wavelength decreases and the data are consistent with a wavelength accuracy about 0.4 nm at 140nm. The results for the dispersion curve of the above liquid are presented.     

Diffraction efficiency of a grating coupler for an array illuminator

The diffraction efficiency of a grating coupler having a surface-relief grating is calculated by the use of coupled-wave theory. The grating couplers are fabricated to examine the validity of the calculated result. The dependence of the measured diffraction efficiency on the groove depth of the grating coupler agrees well with the calculated results. The array illuminator, which emits 10 and 20 beams with equal intensity, is designed and fabricated through the use of these numerical results. The uniformity error of the output beam caused by the error of the diffraction efficiency is also discussed.