R N. Watts

Manipulating atomic velocities using diode lasers

We have used counterpropagating radiation from a diode laser to cool and stop a beam of cesium atoms. The laser frequency was chirped to keep it in resonance with the slowing atoms. The same laser was used to probe the resulting velocity distributions. We have cooled more than 1010 atoms/sec to a temperature of 1 K. This is an extremely simple and inexpensive way to manipulate atomic velocities and has a wide range of possible applications.

Optical constants of in situ-deposited films of important extreme-ultraviolet multilayer mirror materials

We have performed angle-dependent reflectance measurements of in situ magnetron sputtered films of B(4)C, C, Mo, Si, and W. The Fresnel relations were used to determine the complex index of refraction from the reflectance data in the region of approximately 35-150 eV. In the cases of Si, C, and B(4)C we found excellent agreement with published data. However, for Mo and W we found that the optical properties from 35 to 60 eV differed significantly from those in the literature.

Si/B4C narrow-bandpass mirrors for the extreme ultraviolet

We report the results of extreme-ultraviolet reflectance measurements and structural characterization of multilayer mirrors made by sequential sputter deposition of Si and B(4)C. Compared with Si/Mo multilayers, Si/B(4)C have a much narrower bandpass (deltalambda) and better off-peak rejection but lower peak reflectance (R(0)). Mirrors with three different designs gave the following results: R(0) = 0.275 and deltalambda = 0.31 nm at 13.1 nm and normal incidence; R(0) = 0.34 and deltalambda = 1.1 nm at 18.2 nm and 45 degrees ; and R(0) = 0.30 and deltalambda = 2.0 nm at 23.6 nm and 45 degrees . These multilayers exhibited excellent stability on annealing at temperatures up to 600 degrees C.

Interfaces in Mo/Si multilayers

Using state-of-the-art instruments and electron microscopy, the interfaces in Mo/Si multilayer mirrors fabricated by UHV electron-beam evaporation and by sputtering were examined. Peak shifts were observed in the XPS spectra at growth temperatures as low as 50 C, indicating the formation of silicide at the interface. The TEM micrographs showed that, in multilayers, the majority of the silicide formed at Mo on Si interfaces, rather than at Si on Mo interfaces. At 300 C, the multilayer structure is almost completely destroyed by the reaction. Mirrors with d(Mo) of about 40 A performed much better than those with d(Mo) of about 55 A. The Auger depth profiles showed that oxygen uptake in the sputtered samples and in samples evaporated at 200 C is limited to the top Mo layer, while samples evaporated at temperatures below 200 C had oxygen penetration through at least the first few bilayers, indicating that the silicide layers act as diffusion barriers to the oxygen.

A transmission x-ray microscope based on secondary-electron imaging

A design for a transmission x-ray microscope with 20 nm transverse spatial resolution is presented. The microscope, which is based on the electron-optical imaging of the photoemitted electrons from an x-ray shadowgraph, consists of a transmission x-ray photocathode coupled to a photoelectron emission microscope (PEEM—also called a PEM for photoelectron microscope). Unlike the conventional PEEM, which produces a surface map of photoelectron yield, this microscope can provide information on the subsurface properties of thin samples. The analysis of the microscope’s electron-optical performance is based on the evaluation of Gaussian focusing properties and third-order aberration coefficients computed using several complementary methods. The electron optical properties of the microscope are examined with an emphasis on issues affecting overall performance and achieving the best possible resolution. Preliminary experimental results using a cesium iodide photocathode are shown.

Peak reflectivity measurements of W/C, Mo/Si, and Mo/B 4 C multilayer mirrors in the 8–190-Å range using both Kα line and synchrotron radiation

Peak reflectivity measurements of W/C, Mo/Si, and Mo/B(4)C multilayer mirrors have been performed using line and synchrotron radiation in the 8-190 A wavelength range. Short wavelength measurements using a line source were corrected for nonmonochromatic and divergent incident radiation. Reflectivities of Mo/Si mirrors, measured with synchrotron radiation, ranged from 25 to 44% but decreased significantly around the Si absorption edge. Mo/B(4)C multilayer mirrors were measured that had peak reflectivities from 10 to 25% between 90 and 200 A and bandpasses as small as 3 A.

A simple variable line space grating monochromator for synchrotron light source beamlines

Abstract In this paper, we present and analyze an improved spectrometer design that has evolved from studies of the focal properties of transmission gratings in converging ligid beams. This design uses a variable line space grating at a fixed angle of incidence to focus the diffracted light in one dimension, producing resolutions in excess of 1000 over a large wavelength region. Attractive features of this concept include high throughout, simple wavelenght scanning, simple optical elements (plane gratings and plane and toroidal mirrors), and relatively inexpensive realizations. After presenting a mathematical analysis of the primary design features, we discuss implementations of this design both as a spectrometer and as two versions of beamline monochromators. Design parameters for the two monochromators will be given.

Variable Groove Spaced Grating Monochromators for Synchrotron Light Sources

Abstract Several generic spectrometer types have been developed for research using VUV light at synchrotron radiation sources. They all have used gratings with a constant groove spacing and they all have tried to incorporate high resolution, high throughput, rejection of second and higher order radiation, and design simplicity in their construction. The use of gratings ruled with variable spaced grooves to reduce defocus, coma, and spherical aberration was suggested almost twenty years ago. An instrument using this grating concept was built five years ago for conventional sources. The first monochromator using a variable line spaced grating was installed at the National Synchrotron Light Source almost two years ago, and a high resolution version of such an instrument has been built at the Synchrotron Radiation Center operated by the University of Wisconsin. In this presentation we review the development of monochromators using variable line space gratings and the possible applications of this type of instrumentation.

The New NIST/ARPA National Soft X-Ray Reflectometry Facility

We have recently begun a series of upgrades to the NIST/ARPA National Reflectometry Facility at the Synchrotron Ultraviolet Radiation Facility. The facility currently consists of a new monochromator and the original sample manipulator which allows us to measure optical components less than 10 cm in diameter. The monochromator offers high throughput and modest resolution over the wavelength range 3.5–40 nm. In the next year we will be installing a sample manipulator that will be able to accommodate the much larger optics that will be used in future x-ray projection lithography and astronomy instruments. We offer preliminary measurements of the throughput and resolution of the new monochromator.

An evaluation of multilayer mirrors for the soft x ray and extreme ultraviolet wavelength range that were irradiated with neutrons

The Plasma Spectroscopy Group at the Johns Hopkins University develops high photon throughput multilayer mirror (MLM) based soft x ray and extreme ultraviolet (XUV 10 A<λ<304 A) spectroscopic diagnostics for magnetically confined fusion plasmas. The D-T reactions in large fusion reactor type devices such as the International Thermonuclear Experimental Reactor will produce neutrons at a rate as high as 5×1019 n s−1. The MLMs, which are used as dispersive and focusing optics, will not be shielded from these neutrons. In an effort to assess the potential radiation damage, four MLMs (No. 1: Mo/Si, d=87.8 A, Zerodur substrate with 50 cm concave spherical curvature; No. 2: W/B4C, d=22.75 A, Si wafer substrate; No. 3: W/C, d=25.3 A, Si wafer substrate; and No. 4: Mo/Si, d=186.6 A, Si wafer substrate) were irradiated with fast neutrons at the Los Alamos Spallation Radiation Effects Facility (LASREF). The neutron beam at LASREF has an energy distribution that peaks at 1–2 MeV with a tail that extends out to 100 Me...