This PDF file contains the editorial “Editorial: T Minus Six Editorials and Counting” for OE Vol. 29 Issue 06

This PDF file contains the editorial “Book Rvw: Ozone Measuring Instruments for the Stratosphere," edited by William B. Grant for OE Vol. 29 Issue 06

This PDF file contains the editorial “Book Rvw: Optical Integrated Circuits," by Hiroshi Nishihara, Masamitsu Haruna and Toshiaki Suhara for OE Vol. 29 Issue 06

Last year when Jack Gaskill asked me to serve as Guest Editor for this special issue of opitical Engineering devoted to x-ray / EUV optic, he discloused to me Gaskill’s Law, which predictis the number of paper that will be recived in relation to the number invalid.

We describe the implementation of an 8 keV microscope that operates with a conventional x-ray source in our lab. Samples are scanned pixel-by-pixel through a focused x-ray spot produced by a phase-modulating zone plate fabricated with the sputtered-sliced technique. The micro- focused x-ray source uses a Cu target and produces 8 keV photons that are detected with a Si(Li) spectroscopy system. The microscope currently achieves 10 µm resolution.

The development of multilayer optics has profound implications for soft x-ray/extreme ultraviolet (XUV) astronomy. During the October 1987 flight of the Stanford/Marshall Space Flight Center Rocket X-Ray Spectroheliograph, narrow wavelength band, low scatter soft x-ray/extreme ultraviolet spectroheliograms were obtained with ~ 1 arcsec spatial resolution at ? ~ 173 Å (Fe IX, Fe X) and at ? - 256 Å (He II Ly-?). Although the Cassegrain telescopes used in this experiment were small (63.5 mm diameter) and utilized spherical rather than paraboloidal/hyperboloidal mirrors, the images produced exceed in quality any XUV spectroheliograms previously obtained with either normal or grazing incidence techniques. We describe a new rocket spectroheliograph instrument, the MultiSpectral Solar Telescope Array (MSSTA), that is currently being prepared for launch in August 1990. This instrument will utilize true Ritchey-Chrétien optics of 127 mm diameter and parabolic Herschelian optics of 40 mm diameter, which will allow spectroheliograms to be obtained over the soft x-ray/extreme ultraviolet/far ultraviolet spectral range (40 to 1550 Å). The performance of this new instrument should definitely demonstrate the unique combination of ultrahigh spatial resolution and spectral differentiation that multilayer optics afford for astronomical observations. The MSSTA will also represent the first astronomical use of an important new optical device, the multilayer grating. The MSSTA should obtain unprecedented information regarding the structure and dynamics of the solar atmosphere in the temperature range 104 to 107 K.

Metal multilayer mirrors have been designed for the ALEXIS satellite, which is to carry six wide-field telescopes to perform an all-sky survey in three narrow EUV/ultrasoft x-ray wavelength bands. Comprised of alternating layers of molybdenum and silicon, the mirrors are optimized to provide maximum reflectivity at angles from 12.5 to 17.6° off normal incidence and at wavelengths of 133, 171, or 186 Å. Simultaneously, the mirrors use a "wavetrap" to suppress reflectivity at 304 Å, where the extremely strong geocoronal line of He II causes severe background problems. Low reflectivity at 304 Å is achieved by superposing two layer pairs that provide destructive interference with an effective 2d spacing of 152 Å. Calculations predict the 186 Å design will have a peak reflectivity at 186 A of 35% and a 304 Å reflectivity less than 10-5 compared to a peak reflectivity at 186 Å of 40% and 304 Å reflectivity of 3 x 10-3 without the wave- trap. In the laboratory the 304 Å reflectivity on a multilayer sample with a wavetrap has been measured to be as low as 10-4 . We present details of the calculations and laboratory measurements of the reflectivity performance obtained with prototype mirrors.

We report on the conception, fabrication, and characterization of a multilayer beamsplitter for use at oblique incidence in the soft x-ray range. Thin film deposition, conventional patterning, and anisotropic etch techniques are used to produce the self-supporting silicon carbide carrier film. Large-area Mo/C multilayer beamsplitters (1 cm2 ) were fabricated. Experimental results on the reflection and transmission at 1.33 nm are presented and compared with theoretical calculations. The role of the supporting film and the flatness of the structure are addressed. Our process is compared with existing approaches from the literature.

The enhanced reflectance achieved by recent developments in x-ray multilayer technology has made normal-incidence x-ray/EUV telescopes feasible for many applications of interest. Conventional optical designs with obvious advantages over the somewhat cumbersome grazing incidence designs of Kirkpatrick, Baez, and Wolter can thus be utilized. Preliminary results of actual flight data suggest great promise of scientific achievement from this new technology. It is widely recognized that "supersmooth" substrates are required since microroughness can decimate the reflectance of the multilayer. However, high x-ray reflectance is a necessary but not sufficient condition for producing high quality images. A second and equally important condition is the ability to concentrate the reflected radiation in a very small region in the focal plane. Optical substrates with satisfactory "figure" and "finish" for x-ray/EUV applications have been successfully demonstrated. However, small angle scatter from "mid spatial frequency" optical fabrication errors will limit the practical resolution attainable from this promising new technology. The surface power spectral density function over the entire range of relevant spatial frequencies is thus required to accurately predict image characteristics. The results of parametric optical performance predictions indicate that subarcsecond resolution is possible provided sufficiently smooth layer interfaces are maintained. However, optical fabrication tolerances imposed on the substrate may require advances over the current state of the art.

The performance of multilayer x-ray mirrors is improved by smoothing the boundaries within the multilayer stack with ion bombardment at grazing angles of incidence. The process is applied to Co-C and to RhRu-C mirrors for normal incidence telescopes at ? = 63.5 and 114 Å, and the reflectivity is increased by a factor of 2 in both cases. Accumulation of roughness during deposition is eliminated. An estimate of the presently achievable reflectivity for normal incidence mirrors in the ? = 44 to 120 Å wavelength range is given.

Substantial work has been done to characterize filter materials for the vacuum ultraviolet and x-ray regions of the electromagnetic spectrum. This paper summarizes the theoretical basis for predicting performance and compiles the results of different measurement programs for comparison. Recent work that better quantifies transmission as a function of wavelength for various filter and window materials is reported. Other applications of thin films in which these optical properties are important include photocathodes and x-ray laser targets. Of particular interest are figures giving linear absorption coefficients as a function of wavelength for commonly used filter materials. Also included are recent data on the effect of aging on aluminum filters, plus test data and comments on the use of composite materials designed to adjust the bandpass of a filter to meet particular research requirements. The data are presented so that the reader may more easily design and predict the performance of filters and windows for specific applications.

Soft x-ray telescopes require filters that block visible and infrared light and have good soft x-ray transmission. The optical properties of possible materials are discussed, and the fabrication and testing methods for the filters used in a 10-inch normal incidence telescope for ? = 63 Å are described. The best performances in the ? = 44-114 Å wavelength range are obtained with foils of carbon and rhodium

The X-Ray Spectrometer (XRS), which is being developed for one of the focal plane instruments of the Advanced X-Ray Astrophysics Facility (AXAF), requires filters with high x-ray transmittance, high background rejection, and operation at cryogenic temperatures. Thin foil filters can provide high x-ray transmittance and the required rejection for low- energy radiation. The results of the test program demonstrate that these filters are fully successful at cryogenic temperatures and therefore can provide blocking filters for the XRS with the required performance.

Orthonormal polynomials have long been used as a convenient tool to describe optic surface errors. Previously, the products of Fourier and Legendre polynomials have been employed to describe the surface errors for grazing incidence optics. We have applied an alternate set of polynomials, Fourier-Fourier polynomials, to describe the surface errors. This new set differs functionally from the Fourier-Legendre set in that each term has a finite bandwidth frequency spectrum. The advantages of this difference with respect to predictions of grazing incidence telescope performance based on measured surface figure errors are discussed.

Two types of grazing incidence ring resonators for use with free-electron lasers have been investigated. These cavities utilize off-axis conical and flat mirrors and have been designed to operate in the extreme ultraviolet region of the spectrum. In this paper, a design algorithm that calculates the mirror parameters for propagation of Gaussian TEM00 mode beams in the two cavity types is presented. Results concerning the angular stability of each type are also shown.

The ROSAT project is an international collaboration between the Federal Republic of Germany, the United Kingdom, and the United States. The satellite, due to be launched in June 1990, carries a payload of two coaligned imaging telescopes: the German X-Ray Telescope (XRT), which operates in the soft x-ray band (0.1 to 2 keV or 6 to 100 Å), and the UK Wide Field Camera (WFC), which operates in the XUV band (0.02 to 0.2 keV or 60 to 600 Å). ROSAT will perform two main tasks in its anticipated two to four year lifetime: a six-month all-sky survey in the soft x-ray and XUV bands followed by a program of pointed observations for detailed studies of thousands of individual targets. In this paper we review the design and performance of the WFC. The instrument is a grazing incidence telescope comprising a set of three nested, Wolter-Schwarzschild Type I, gold-coated aluminum mirrors with a microchannel plate detector at their common focus. Thin plastic and metal film filters define the wavelength passbands.

The first satellite in a planned series of Soviet astronomical x-ray and gamma-ray satellites will be equipped with two high-throughput telescopes to be manufactured by the Danish Space Research Institute. The optical system consists of two sets of nested cones, whose substrate is aluminum foil. The smooth surface is obtained by dip lacquering, and the reflective layer is gold. The design parameters have been optimized for high throughput at 7 keV. The mechanical design and the status of the surface preparation technologies are described. Various x-ray and optical test facilities for the measurement of surface roughness, "orange peel," and figure errors are described. An optical parallel beam has been established, and results from the first mounted mirrors are discussed. The design goal is an angular resolution of 2 arcmin (half energy width). The first results seem to indicate that this is feasible and the possibility of going down to 1.5 arcmin exists.

In this paper scanning tunneling microscopy (STM) measurements of x-ray mirrors are presented. The x-ray mirrors are 0.3 mm thick dip-lacquered aluminum foils coated with gold by evaporation, as well as state-of-the-art polished surfaces coated with gold, platinum, or iridium. The measurements reveal that the surfaces consist of islands with different topographic features. The microroughness is found to be in the range from 7 to 15 Å, and the characteristic length scale for this microroughness is estimated to be between 0.03 and 0.06 |xm. For the thin foil mirrors it is found that the microroughness depends on the thickness of the gold layer. The roughness is smallest (~ 7 to 9 Å) for gold layers between ~ 100 and ~ 250 Å, and it becomes significantly greater (~10 to 15 Å) for gold layers thicker than ~ 350 Å. With a few exceptions the STM measurements agree well with recent x-ray studies. The results can be used as a guide when selecting the best coating process in the production of x-ray mirrors.

Zernike polynomials have been used for some time to fit wavefront deformation measurements to a two-dimensional polynomial. Their orthogonality properties make them ideal for this kind of application. The typical procedure consists of first obtaining the fitting using x-y polynomials and then transforming them to Zernike polynomials by means of a matrix multiplication. Here, we present a new method for making this fitting faster by using a set of orthogonal polynomials on a discrete base of data points on a unitary circle.

Diode-pumped cw lasers operating between 2 and 3 µm in the heavy rare-earth activator ions are reviewed. In Ho,Tm:YAG we demonstrated high efficiency using Tm as the sensitizer ion, which absorbed the pump radiation. This is followed by a cross-relaxation process, which allows two excited Tm ions to be produced from one absorbed photon. There is rapid energy migration among the Tm ions, followed by energy transfer to the Ho ion. The 2 pm laser action is to a level 460 cm-1 above the ground state. In Tm,Ho:YLF we demonstrated cw cascade laser emission at 2.31 and 2.08 µm. Above threshold for both transitions, two infrared photons are produced for each absorbed pump photon. The theoretical slope efficiency of this system is 72.3% for pumping at 0.791 µm. In Er:YLF, cw laser emission at 2.8 pm with a 10% slope efficiency was demonstrated. The laser transition is normally self-terminating, but an upconversion process, which depopulates the lower laser level and populates the upper laser level, allows this transition to operate in a cw mode.

A commercial GaAIAs injection laser is frequency locked to the Rb (D2) transition. A relative frequency stability of 400 Hz is measured for a 24-s averaging time. The frequency stability of this device with only temperature control is 4 kHz. This is a factor of 20 improvement in the state of the art for temperature control stability for semiconductor lasers.

We have constructed a five-telescope beam combiner composed of standard single-mode fiber optics and directional couplers. The device has good thermal and polarization stability, high throughput, and allows simultaneous measurement of all 10 possible interference pairs. It is connected to a small five-telescope interferometer, which is used to make synthetic aperture images

Logic gate processing with a new configuration of coding cells using one-dimensional spatial encoding cells is proposed. Applications of the proposed method, i.e., an optical array processor that can perform parallel operation of addition and subtraction for two binary variables without considering the carry mechanism, and gray-level image processing are presented. Experimental verifications are also performed.