Tolerancing of diffraction-limited Kirkpatrick-Baez synchrotron beamline optics for extreme-ultraviolet metrology.

The recent interest in extreme-ultraviolet (EUV) lithography has led to the development of an array of at-wavelength metrologies implemented on synchrotron beamlines. These beamlines commonly use Kirkpatrick-Baez (K-B) systems consisting of two perpendicular, elliptically bent mirrors in series. To achieve high-efficiency focusing into a small spot, unprecedented fabrication and assembly tolerance is required of these systems. Here we present a detailed error-budget analysis and develop a set of specifications for diffraction-limited performance for the K-B optic operating on the EUV interferometry beamline at Lawrence Berkeley National Laboratory's Advanced Light Source. The specifications are based on code v modeling tools developed explicitly for these optical systems. Although developed for one particular system, the alignment sensitivities presented here are relevant to K-B system designs in general.

Comparison of mechanically ruled versus holographically varied line-spacing gratings for a soft-x-ray flat-field spectrograph.

Recent progress in the design of aspheric wave-front recording systems has permitted the manufacture of holographic gratings with highly variable groove densities that are suitable for flat-field spectrographs. A holographic grating thus recorded was processed to produce a laminar profile by use of reactive-ion etching. Measurements are reported of the absolute diffraction efficiency of this grating and of a comparable mechanically ruled grating. It is found that the holographic grating is much more effective in suppressing the higher orders. The spectral resolution was determined by use of a carbon Kalpha x-ray generator and a spectrograph with an imaging detector. The spectral resolution of the holographic grating was approximately 3 times worse than that of the ruled grating.

High-resolution tunable spectrograph for x-ray laser linewidth measurements with a plane varied-line-spacing grating.

We describe a spectrograph for x-ray laser linewidth measurements in the range 100-220 A. The design employs a plane varied-line-spacing grating operating in the convergent light produced by imaging of the entrance slit with a concave spherical mirror. By the appropriate choice of the linear term in the grating-spacing variation, two separate wavelengths can be focused at the same image distance. As a result all wavelengths within the range of interest are focused at or near the same distance. The spectrograph can be tuned by rotation of the grating to bring any wavelength within the range to the center of the focal plane, and the spectra are dispersed on a surface that is erect or practically flat and perpendicular to the principal ray. This allows the use of a planar detector. With a streak camera used as a detector, the instrument obtained time-resolved linewidth data on x-ray lasers with a resolving power of 1 x 10(4) to 2 x 10(4). This paper presents the design methods used to optimize the varied-line-spacing grating, the design of the tunable spectrograph, and the results from the instrument in operation.

Molybdenum/beryllium multilayer mirrors for normal incidence in the extreme ultraviolet.

We report on a series of normal-incidence reflectance measurements at wavelengths just longer than the beryllium K-edge (11.1 nm) from molybdenum/beryllium multilayer mirrors. The highest peak reflectance was 68.7 ± 0.2% at λ = 11.3 nm obtained from a mirror with 70 bilayers ending in beryllium. To our knowledge, this is the highest normal-incidence reflectance that has been demonstrated in the 1-80-nm spectral range.

Sex ratios at birth in Micronesia: reply to James.

PIP: In response to comments of William H. James on the authors' articles, it is stated that Micronesian populations are now and have been in the past characteristically highly masculinized at birth (i.e., secondary sex ratios [SSR] of over 108-110). It is fascinating to examine how this finding may reflect microevolutionary change in this island setting. Aspects of reproductive behavior in Micronesia were examined for clues to proximate/remote mechanisms that may promote this pattern of male versus female births. One of the most singular defining features of the reproductive pattern of these groups is high coital rates, maintained against age and marriage duration. It is argued that SSR patterns in Micronesia are a corollary of the unique biobehavioral reproductive features of these island groups, which includes high coital rates. Professor James' concerns relate to 2 considerations: 1) the statistical aspect of results from small scale populations, and 2) the veracity and reliability of results from ethnographic research. Methodologies employed by modern ethnographers entail extensive and intensive cross-checking, multiple verification, and repeated re-evaluation of information collected from a large number of independent sources. In the Butaritari case, conclusions are drawn from several very different but consistent lines of evidence that show coital rates are maintained with age and marriage duration in this group: ethnographic data showing the marriage relationship maintains a highly sexualized environment, demographic data showing no effective reduction in fertility through the first 2 decades of marriage. In the case of the sex ratios, almost all births in these populations over the last century have been covered, and sample sizes in the thousands are available. These are acceptable for use of chi-square and sufficient to make inferences about variations in sex ratios by age group as they relate to coital activity.^ieng

Phase-retardation and full-polarization analysis of soft-x-ray synchrotron radiation close to the carbon K edge by use of a multilayer transmission filter.

We have produced a multilayer transmission filter with 100 periods of Cr/C to achieve a significant phase retardation while maintaining good transmission for photon energies just below the carbon K edge. This device was installed into a polarimeter behind the SX700/3 monochromator at the Berlin synchrotron radiation laboratory, BESSY. The phase-retardation properties were observed as theoretically predicted. Agreement between experiment and calculation could be obtained by introduction of a rather small interface roughness in the simulation code (σ = 0.65 nm rms). An observed phase retardation of 5° was sufficient to permit, for the first time we believe, a complete and unambiguous polarization analysis of soft-x-ray synchrotron radiation (265-eV photon energy) with primary standards.

Secondary sex ratios in Micronesian populations.

Secondary sex ratio (SSR) values in excess of 109 male for every 100 female livebirths have been reported from several Micronesian populations. Analyses of linked family records dating from before 1942 for the native people of Guam reveal a highly masculinized SSR even at high birth orders and parental ages of married fertile couples. These findings contrast with reported declines in SSR with parity and parental age among historical and modern populations in Europe and North America where such declines often have been ascribed to the effects of decreasing mean coital frequencies associated with marital duration and spousal age. This study challenges implicit assumptions about the supposed universality of Euroamerican patterns of marital sexual behavior and supports the coital frequency hypothesis of SSR determination.

PIP: There have been reports of male:female secondary sex ratios (SSR) from several Micronesian populations which are higher than 109:100 live births. Based upon data from a linked family register of 38,884 records for the native population of Guam before World War II in the Pacific, the authors found an highly masculinized SSR even at high birth orders and parental ages of married fertile couples. These findings contrast with reported declines in SSR with parity and parental age among historical and modern populations in Europe and North America attributed to the effects of decreasing mean coital frequencies associated with marital duration and spousal age. Study findings therefore challenge implicit assumptions about the universality of Euroamerican patterns of marital sex behavior and support the coital frequency hypothesis of SSr determination.

Tarnishing of Mo/Si multilayer x-ray mirrors.

Multilayer x-ray mirrors of molybdenum and silicon operating at normal incidence at energies just below the Si L(II,III) absorption edges are a key component in the development of soft-x-ray projection lithography. In this application high reflectivity is essential. Aging tests on such reflectors, with Mo as the last layer deposited, show that the structures decline in reflectivity with time when stored in air. Chemical analysis of a well-aged surface by photoelectron spectroscopy techniques reveals that the uppermost Mo layer eventually becomes completely oxidized to MoO(3) and MoO(2) and contaminated with carbonaceous materials. The oxidation can be prevented by storing the mirrors in an oxygen-free atmosphere or by depositing the silicon as the top layer. The reflectivity of tarnished mirrors can be restored by removing the oxides by argon-ion etching or wet chemical methods.

Investigation of Damage to Multilayer Optics in X-Ray Laser Cavities: W/C, WRe/C, WC/C, Stainless-Steel/C, and Cr3C2/C Mirrors.

In many applications, multilayer mirrors are exposed to damaging fluences of x rays. In x-ray laser cavities intense optical and broad-band x radiation, from the x-ray laser plasma amplifier, can damage multilayer mirrors on time scales of hundreds of picoseconds. We describe experiments using short duration (500 ps) bursts of soft x rays from a laser produced gold plasma to damage multilayer mirrors designed to reflect wavelengths close to 45 Å at normal incidence. The effect of the damaging x-ray flux on normal incidence reflectivity was time resolved for W/C, WRe/C, WC/C, 303-stainless-steel/C, and Cr3C2/C multilayers. The damage thresholds of the different mirrors were compared, and the Cr3C2/C mirrors were found to be the most resilient. The outer layers of the multilayers were observed to expand slowly as x rays were absorbed, and a more rapid expansion then preceded the total loss of reflectivity, at temperatures well below the melting temperature of the mirror components. It is believed that the dominant expansion mechanism is a change in the amorphous carbon layers to a more graphitic structure. The data are fit quite well by a model that assumes expansion of up to 25% in the thickness of the outermost carbon layers, followed by intermixing of the hotter layers. The rapid expansion has been observed to occur in times from 40 to 150 ps and may be the fastest resolution to date of the phenomenon of graphitization. The integrated reflectivity of the mirrors was observed to increase by up to a factor of 2.5 as they damaged; this reflectivity increase may be consistent with a reduction in the layer roughness.

A Soft X-Ray/EUV Reflectometer Based on a Laser Produced Plasma Source.

A soft x-ray reflectometer is described which is based on a laser-produced plasma source and is continuously tunable over the range 40 Å < λ < 400 Å. The source is produced by focusing 0.532-µm light from a Q-switched Nd:YAG laser on a solid target. The x-ray wavelength is defined using a high throughput spherical grating monochromator with moderate resolving power (λ/Δλ ≈ 100 to 500). A time-averaged monochromatized flux of more than 109 photons/s in a 1% bandwidth at 100 eV is obtained. Photon "shot noise" limited measurements are obtained by the use of an I0 detector to normalize out the shot-to-shot variations in source intensity. Measurements with submillimeter spot sizes are readily obtainable. Various detectors have been used and the advantages and disadvantages of each are discussed. The higher order contamination of the monochromator output has been analyzed using a second grating for the purpose of making measurement corrections. The reflectometer thus provides the capability for precision absolute measurements of the reflectance of gratings and multilayer mirrors, the transmittance of thin film filters, or other properties of x-ray optical elements.

Birth seasonality and the etiology of neurodegenerative diseases in the native population of Guam.

Analyses of data from a linked family register for the native population of Guam reveal marked birth seasonality in nearly 27,000 livebirths registered during the period 1901-1941. In contrast to a November peak for all births, victims of amyotrophic lateral sclerosis (ALS) who died between 1947 and 1984 show a maximum birth peak in February while those afflicted with parkinsonism-dementia (PD) and dying during this period exhibit a bimodal pattern of births peaking in April and October. Birth seasonality in victims of neurologic diseases, including ALS and parkinsonism, has also been reported from Japan. Intensive clinical, genetic, epidemiologic, and other investigations over more than three decades, while noting familial patterns of occurrence, fail to reveal any simple pattern of genetic transmission in the etiology of ALS/PD among natives of Guam, site of one of three hyperendemic foci in the Pacific area for ALS. Several environmental agents have been proposed to account for familial, temporal, and local patterns of occurrence, although no hypothesis has remained unchallenged. This report reviews evidence of birth seasonality in relation to patterns of cycad ingestion, rainfall seasonality, and prevailing morbidity patterns of the period. Despite earlier failures to identify antibody markers or a slow-acting virus in ALS victims, the probable role of an arbovirus in a complex etiology of the disease is presented. © 1992 Wiley-Liss, Inc.

Seasonality of vital events in a Pacific Island population.

Analyses of vital data derived from a family record register for the native population of Guam reveal significant variations in births, deaths, and marriages over the period 1901-41. Although lacking marked photoperiod or temperature changes of temperate zones, the tropical island is subject to marked seasonal differences in rainfall characteristic of western Pacific islands. Marital patterns exhibit troughs associated respectively with the Lenten period and with Christmas celebrations. Infant and childhood deaths show close correspondence with rainfall patterns, consistently exceeding expected values during the rainy season (July-November) when conditions are optimal for the spread of communicable and gastrointestinal diseases. Births attain a peak in November, or at the beginning of the more advantageous season for infant health and survival. Seasonality in vital events, reported for many Euroamerican and some African and Asian populations of modern and historical periods, has rarely been documented for native populations of the tropical Pacific. Comparisons of differences in these patterns among different populations in varied environments provide unique opportunities to evaluate causal models of interactions among biological, sociocultural, and physioenvironmental factors.

PIP: Research of seasonal differences in patterns of vital events in selected populations allows evaluation of causal models of interaction among biological, sociocultural, and physioenvironmental factors. Accordingly, vital data were analyzed from a family record register for the native population of Guam over the period 1901-41. Though Guam lacks marked temperature and photoperiod changes, it is subject to marked seasonal differences by rainfall. Investigation revealed significant variations in births, deaths, and marriages. Marital seasonality was closely linked to calendar events of the Catholic Church. Specifically, marriage peaks preceded and followed the Lenten period, with a secondary trough occurring during Advent. The incidence of infant and childhood deaths closely correlated with seasonal fluctuations in rainfall. Mortality consistently exceeded expected levels during rainy seasons when communicable and gastrointestinal diseases are most readily spread. In turn, births peaked in November at the beginning of the close of the rainy season which commences in July. Newborns arrived at the beginning of the season most conductive to engendering infant health and survival.

Population history of Nauru: a cautionary tale.

"Available records relating to Nauruan population attributes are critically evaluated to develop a reconstructed population history of this native Micronesian people. Historical evidence consists of documentation of the effects of diseases and modern warfare and more recent behavioral changes traceable to altered economic conditions. Unpredictable and dramatic fluctuations in population characteristics throughout the historic period are revealed, precluding the use of standard population models. Even structural similarities at widely separated time periods are shown to be insufficient evidence of stable population conditions, a cautionary finding for paleodemographers, archaeologists, and others working throughout the Pacific."

Grazing incidence technique to obtain spatially resolved spectra from laser heated plasmas.

An experimental method is described in which a grazing incidence spectrograph is used to obtain spatially resolved spectra of laser heated plasmas in the 6-370-A region. In the experiment, small target spheres were irradiated by tightly focused laser beams. A tilted grazing incidence elliptical mirror placed 1.3 m from the target focuses the plasma radiation on the spectrograph slit at a distance of 0.7 m producing a useful degree of spatial resolution in the recorded spectral lines. The spectrum from a copper target is presented together with an x-ray pinhole camera image of the plasma.

X-ray Photographs of a Solar Active Region with a Multilayer Telescope at Normal Incidence.

An astronomical photograph was obtained with a multilayer x-ray telescope. A 4-centimeter tungsten-carbon multilayer mirror was flown as part of an experimental solar rocket payload, and successful images were taken of the sun at normal incidence at a wavelength of 44 angstroms. Coronal Si-XII emission from an active region was recorded on film; as expected, the structure is very similar to that observed at O-VIII wavelengths by the Solar Maximum Mission flat crystal spectrometer at the same time. The small, simple optical system used in this experiment appears to have achieved a resolution of 5 to 10 arc seconds.