Determination of the absolute intensity of vacuum ultraviolet radiation presents unique problems. This is primarily caused by the fact that over most of this spectral region (0.2-200 nm) the radiation cannot pass through windows or gases at atmospheric pressure. On the other hand, the ionizing properties of vacuum ultraviolet radiation are a decided advantage in providing specific means for absolute intensity measurements.

We have developed a Penning discharge lamp for use in the calibration of instruments and components for the extreme ultraviolet. This source is sufficiently light and compact to make it suitable for mounting on the movable slit assembly of a grazing incidence Rowland circle monochromator. Because this is a continuous discharge source, it is suitable for use with photon counting detectors. Line radiation is provided both by the gas and by atoms sputtered off the interchangeable metal cathodes. Usable lines are produced by species as highly ionized as Ne IV and Al V. The wavelength coverage provided is such that a good density of emission lines is available down to wavelengths as short as 100Å. This source fills the gap between 100 and 300Å which is inadequately covered by the other available compact continuous radiation sources.

A high intensity electron-impact x-ray source using a one-dimensional Pierce lens has been built for the purpose of calibrating a bent crystal x-ray spectrometer. This source focuses up to 100 mA of 20-keV electrons to a line on a liquid-cooled anode. The line (which can serve as a virtual slit for the spectrometer) measures approximately 800 µ x 2 cm. The source is portable and therefore adaptable to numerous types of spectrometer applications. One particular application, the calibration of a high resolution (r = 104) time-resolved crystal spectrometer, will be discussed in detail.

XUV radiation from a laser-produced plasma was investigated using a 1.5 m grazing incidence monochromator with a channel electron multiplier array detector. This instrument provides relatively high spectral resolution as well as linear response over a large dynamic range. Spectra from 8 to 40 nm were obtained from plasmas generated by a 0.5 J Nd:YAG laser focused on the following different target materials: Al, Cu, Fe, Sn, Sm, Hf, Yb, W, and Pb. Reproducibility of emission and effects of laser energy and focus on the output were measured.

Historically, x-ray output of flash x-ray tubes was maximized empirically by changing the electrode geometry and varying the capacitance of the pulse generator. With the advent of high-voltage, low-impedance transmission lines, short-duration, high-current pulses could be generated with ease. An appropriate line scaling should assure that dose maximization is not reached at the expense of pulse prolongation which would reduce stop motion capability, but rather that dose rate should be maximized. Additionally, anode evaporation in the arc phase should be minimized to enhance tube life. Typically, the impedance of flash tubes changes during the discharge from infinity in the beginning to nearly zero in the arc phase and, either for field emission or high-vacuum discharge tubes, can well be modeled by a time-varying ohmic resistor Zx(t). Using a modification of Bergeron's method of travelling wave analysis, transient tube voltage and current can be determined out of a closed-form solution. This allows to calculate corresponding dose rate-time profiles of each spectrum. An ideal pulsed transmission line, charged up to a dc potential U0, has been assumed, characterized by its characteristic impedance Z0 and characteristic time T. Three typical examples illustrate the importance of optimum line scaling and K-series excitation voltage on tube performance such as dose, maximum dose rate, discharge delay time and pulse width. These examples encompass a transmission line with (a) constant initially stored energy E0 = UO2T/4Z0, but various combinations of Zo and T; (b) increasing energy E0 by decreasing Z0, but T = const; and (c) constant line parameters Z0 and T, but assumption of various Zx(t) profiles. Basic matching rules have been worked out in order to approach ideal operation for a given tube impedance time profile. A parametric analysis revealed that, with decreasing pulser impedance, there are increases in the bremsstrahlung and K-series radiation emissions, but that the pulse delay time and pulse width also increase, thus limiting applications to high-rate phenomena. A detailed description of the method and results which are also applicable to an ideal Blumlein line will be published elsewhere.

When an X-ray beam is not monochromatic, the transmitted flux through an absorber is not an exponential function of the absorber thickness. Instead, it may be a sum of two, three, or more exponential functions depending on whether the beam contains photons of two, three, or more different energies. This work shows that if the thickness of a gaseous absorber is continuously varied by adjusting the gas pressure, the relative strength of different harmonics in the monochromator output can be determined. This method also provides an accurate means to measure the absolute cross section of the gas molecules, and in conjunction with a modified Samson type ion chamber may also be used to measure the absolute photon flux as well.

The calibration of photon counting imaging detectors for satellite based EUV astronomy is a complex process designed to ensure the validity of the data received "in orbit". We describe and illustrate the methods developed to accomplish calibration of microchannel plate detectors for the Extreme Ultraviolet Explorer (EUVE). The characterization of these detectors can be subdivided into three categories, stabilization, performance tests and environmental tests.

We have built a 1 meter normal incidence telescope, with a normal incidence concave diffraction grating spectrometer at its focus. The instrument's spectral coverage is 350 to 1150 Å with a spectral resolution of 5 Å and a peak effective area of 6 cm2 at 500 Å . The instrument was launched on an Aries sounding rocket on November 27, 1983 in an effort to determine the hydrogen and helium abundance in the local interstellar medium. Here we present a description of this instrument with the primary emphasis on the methods used to calibrate it.

Two methods which together allow sensitivity calibration from 20 Å to 430 Å are described in detail. The first method, useful up to 120 Å, uses a low power source to generate K∝ X-rays which are alternately viewed by an absolute detector (a proportional counter) and the spectrometer. The second method extends that calibration to 430 Å. It relies on the 2:1 brightness ratio of bright doublet lines from impurity ions which have a single outer shell electron and which are present in hot, magnetically confined plasmas. It requires that the absolute sensitivity of the spectrometer be known at one wavelength point, and in practice requires a multi-element spectral detector.

A spectrometer has been developed specifically for the x-ray laser effort at Lawrence Livermore National Laboratory (LLNL). The instrument takes advantage of the small divergence and size of the lasing source by positioning all three components - the source, a custom-ruled grating, and a microchannel plate (MCP) detector - on the Rowland circle. The sum of incident and diffracted angles is kept constant. Illuminating a pinhole at the source location with a z-pinch produces wavelength calibration at several energy ranges in the 65- to 200-eV interval. The same source used in conjunction with the MCP camera and Kodak 101 film yields the absolute detector efficiency. Ion bombardment of a beryllium target at the source location produces the x-rays necessary to determine the absolute efficiency of the grating-detector combination at 107 eV. Grating efficiency is then deduced from the MCP efficiency at that energy. Three 25-Ω stripline structures on the MCP allow sub-nanosecond gating of the spectrometer, which improves the signal-to-background ratio. The rise time response of the entire MCP detector-cable assembly is about 200 ps. We also measured the transmission of the filters that are used in suppressing ultraviolet backgrounds.

A method of absolute calibration of a VUV spectrometer-detector system is presented in which continuum synchrotron radiation is used. Calibration of the optical system is performed for the purpose of absolute measurements of electron impact photoemission cross sections for discrete atomic (molecular) transitions in the VUV wavelength region. A large computer-controlled multiadjustable manipulator is used for positioning the spectrometer-detector system with respect to a beam of synchrotron radiation. The manipulator allows rotation with respect to two perpendicular axes, one collinear with the electron beam, and the other collinear with the spectrometer entrance slit. Using these rotations, a beam of synchrotron radiation is scanned across the grating surface resulting in a precise simulation of the source geometry encountered in the electron-atom collision source. In this way the absolute response of the spectrometer-detector system and the geometrical factors encountered in the electron-atom source are determined in an integral fashion allowing absolute photoemission cross sections to be determined with unparalleled precision.

An absolute intensity calibration of the SPRED VUV spectrograph currently in use on the Tokamak Fusion Test Reactor (TFTR) has been performed using synchrotron radiation from the NBS SURF II electron storage ring. Calibration results for both the 450-g/mm and 2100-g/mm gratings are presented and details of the calibration procedure are discussed.

A 22 x Wolter microscope was calibrated after several months of operation in the Lawrence Livermore National Laboratory (LLNL) Inertial Confinement Fusion program. Placing a point x-ray source at the microscope focus, I recorded the image plane spectrum, as well as the direct spectrum, and from the ratio of these two spectra derived an accurate estimate of the microscope solid angle in the 1-4 keV range. The solid angle was also calculated using the microscope geometry and composition. Comparison of this calculated value with the solid angle that was actually measured suggests contamination of the microscope surface.

The responses of gold cathode photoelectric detectors to photons in the 3 to 7.5 keV energy band have been measured using synchrotron radiation. The photoelectron detectors under study have cathodes with a conical configurations. Their sensitivities with respect to position on the cathode are nearly uniform (within 30 percent) over approximately 65 percent of the cone surface. The responses fall rapidly near the outer edges. Sensitivities with respect to the photon angle of incidence are proportional to (sin θ)-1. In the photon energy band covered, the measured response of the detectors are approximately 20 percent lower than the responses measured with conventional x-ray sources. These differences are due to differences in the geometries of the two calibrations.

Recent advances in pulsed plasma research, materials science, and astrophysics have required many new diagnostic instruments for use in the low energy x-ray regime. The characterization of these instruments has provided a challenge to instrument designers and provided the momentum to improve x-ray sources and dosimetry techniques. In this paper, the present state-of-the-art in low energy x-ray characterization techniques is reviewed. A summary is given of low energy x-ray generator technology and dosimetry techniques including a discussion of thin window proportional counters and ionization chambers. A review is included of the widely used x-ray data bases and a sample of ultra-soft x-ray measuring techniques is discussed. These techniques include sub-femtoampere current measuring procedures, chopped x-ray source generators, phase sensitive detection of ultralow currents, and angular divergence measurements.

During the fabrication of the mirrors for the Extreme Ultraviolet Explorer (EUVE), we have developed methods for evaluating the surface quality of our optics. Measurement of soft x-ray scattering profiles allows us to determine the surface roughness and correlation lengths for highly polished metal surfaces. With this method, we have determined the surface param-eters for one of the Wolter Schwarzschild Type I mirrors that we have fabricated for the EUVE mission. We present the techniques employed, the theoretical basis for our method, and the data that we have taken. Our measurements show that our best mirrors have a surface roughness of 20Å RMS or less.

Extensive grating calibration facilities have been developed at the Space Sciences Laboratory at Berkeley, which are now being used for the evaluation of the gratings for the spectrometer on the Extreme Ultraviolet Explorer. Measurements of efficiency scattering and imaging quality can be made at wavelengths from 44Å to 2500Å.

The calibration of crystal integrated reflectivity can be faithfully performed with an uncollimated, well-filtered point x-ray source. In this geometry the angle of illumination of the crystal greatly exceeds the crystal rocking angle. The crystal essentially collimates the scattered beam, establishing the detector acceptance angle. We have measured single crystal Rc's in this way for a variety of crystals including PET, Beryl, LiF (200), several synthetic multilayers, silicon (111), and KAP. In addition we report the first measured Rc for convex curved metal multilayer crystals.

X-ray spectral analysis plays a major role as a diagnostic for hot, dense plasmas. Various diffraction media are utilized as flat or convex-curved surfaces for collecting soft x-ray spectral data in the 200 eV - 2 keV energy range. Calibration of the diffracting surface provides means for absolute line emission measurements from plasma generating sources i.e., pulsed-discharge gas puff and focused laser-target interaction experiments. The purpose of this work is the evaluation and absolute intensity calibration of diffraction surfaces consisting of grown crystals (acid phthalate), naturally occurring crystals (beryl) and surfaces formed by vacuum deposition (multilayered structures). The sources and experimental equipment used for the calibration work were: 1) a conventional sealed x-ray tube, x-ray fluorescer, and a single-crystal spectrometer, 2) a soft x-ray facilities incorporating a Henke tube with demountable anodes and double-crystal spectrometer.

We have been developing ultrathin multilayered plastic foils for use as radiation entrance windows in satellite borne position sensitive proportional counters (PSPC) for imaging ultrasoft X-rays from celestial sources. The access windows are supported by two mechanical grid systems. The techniques to prepare and manufacture the access windows will be described. Results of measurements of individual windows as well as imaging performances of PSPC's equipped with specified windows will be given.

The methods of calibrating the filters used on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite are described. EUVE will conduct the first all-sky survey in the entire EUV band (68Å-912Å). The filters determine 4 spectral bands in the survey telescopes and act as order filters in the spectrometer telescope. The four flight filter types used are: Lexan/Boron, Aluminum/Carbon, Indium/Tin, and Titanium/Antimony. The measurement of the filters' transmission properties from the soft x-ray to the far UV using a grazing incidence monochromator is discussed. Three radiation sources are used: a hollow cathode discharge source, a continuous discharge Penning source, and a Henke type target x-ray tube. A particle ingress test to determine the ability of the filters to inhibit energetic particles in earth orbit from entering the detector and increasing the background is described. Other filter tests include lifetesting in different storage and operating environments to measure the filters' transmission stability. Problems encountered in calibrating these four filter types are also presented.

Spectral sensitivity of a soft x-ray streak camera (hv=0.1-1.5 keV) was absolutely calibrated by using x-ray diodes and x-ray film; coupled with a transmission grating spectrometer. Distortion of the output image due to time and space nonlineality of the streak camera system was corrected by computer aided processing. A new analyzing data-reduction method of the x-ray spectum from the multifiltered XRD signals is also described.

The Lawrence Livermore National Laboratory (LLNL) has been a pioneer in the field of x-ray diagnostic calibration for more than 20 years. We have built steady state x-ray sources capable of supplying fluorescent lines of high spectral purity in the 100-eV to 100-keV energy range, and these sources have been used in the calibration of x-ray detectors, mirrors, crystals, filters, and film. This paper discusses our calibration philosophy and techniques, and describes some of our x-ray sources. Examples of actual calibration data are presented as well.

The calibration facility at the University of Colorado is being used to evaluate the performance of optics in the soft x-ray and EUV. Using either a hollow cathode gas discharge EUV source or a focussed electron impact x-ray source, we are able to generate light with wavelengths ranging from 2.7 A to 2500 A. Monochromaticity is achieved with a grazing incidence monochromator and filters. The light enters a large vacuum chamber where it illuminates the sample being studied. Standard detectors include a flowing gas proportional counter, a resistive anode MCP, and an NBS photodiode. The optics and detectors are remotely positioned inside the vacuum chamber using computer controlled stepping motor stages. Data acquisition is also computer controlled. Further data processing is performed on a VAX 8600. We have used the facility to evaluate the performance of diffraction gratings, multilayer mirrors, reflective coatings, spectrographs, surface roughness scattering, and absolute detector efficiencies. We present a complete description of the instrumentation and some recent results.

The National Bureau of Standards supports a research and development program in the vacuum ultraviolet and soft x-ray region of the spectrum with the goal of providing radiometric source and detector standards for measurement applications. Windowless photodiodes are calibrated for absolute quantum efficiency in the spectral range 5 nm-122 nm (250 eV-10 eV) with estimated uncertainties of 8-15%. The primary standard used in these calibrations is a rare gas ionization chamber. The measurement program utilizes the NBS 300 MeV Synchrotron Ultraviolet Radiation Facility, SURF II, which has two dedicated beam lines for radiometric research and calibration activities. One of these beam lines supports detector radiometry. The second is dedicated to the calibration of spectrometric instruments in the wavelength range from about 4 nm (300 eV) up into the visible. The photon flux of the synchrotron radiation beam at the entrance aperture of the user's instrument is known to within an uncertainty of from 2 to 6%, depending upon wavelength. The presentation will review these instrument and detector calibration services and also describe several soft x-ray measurement-related research projects where NBS staff and visiting scientists have been active.

Many beam lines have become available at storage rings and synchrotrons around the world, presenting the opportunity to use them as calibration sources in the VUV, soft and hard X-ray regions. Synchrotron radiation is unique in offering a high intensity, highly polarized, continuous spectrum in a single source. Other important characteristics such as high brightness, narrow or broad spectral width, degree of polarization, and spectral purity depend on a beam line's optics. A typical beam line at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory will have photon fluxes of approximately 1011 photons/sec with resolution (Δe/e) of greater than 7x10-4 into areas of 1 to 30 mm2. The characterization of these sources and their use for calibration of diverse x-ray instrumentation are discussed. Illustrative data for PIN and photoelectron x-ray detectors is given.

We describe the design and performance of the Los Alamos VUV synchrotron radiation beamline, U3C, on the VUV ring of the National Synchrotron Light Source at Brookhaven National Laboratory. The beamline uses separate function optics to collect and focus the horizontally and vertically diverging beam. The monochromator is a grazing incidence Roland circle instrument of the extended grasshopper design (ERG). A post monochromator refocusing mirror is used to focus or collimate the diverging beam from the monochromator. The beamline control and diagnostics systems are also discussed.

A summary is given of characteristics of x-ray sources used by Los Alamos National Laboratory to calibrate various x-ray diagnostic packages and components. Included are D.C. sources in electron impact and fluorescence modes, a pulsed laser source for soft x rays with 100 ps time resolution, Febetron pulsed electron impact sources, and both EUV and x-ray synchrotron beamlines.

A versatile differential pumping system which consists of two independently pumped chambers connected with one of three interchangeable vacuum barriers and various optical elements is described. The three vacuum barriers are a straight tube collimator, a stainless steel capillary array, and a glass capillary array. The vacuum barriers were designed to handle different beam sizes, intensities, and vacuum isolation. The UHV chamber can reach a pressure below 5.0E-10 torr and can sustain a vacuum differential of greater than 1.0E 3 across the barrier. The main advantages of this system are the interchangeable vacuum barriers, the ability to provide control and analysis of the x-ray beam, and the quick ambient to vacuum turn around time. Some experience and data on the operation of this system at the Brookhaven synchrotron are presented. Some characteristics of the vacuum barriers are also discussed.

Accurate measurements of the Sun's extreme ultraviolet (EUV) emission are of major importance in aeronomical studies of the Earth's upper atmosphere and for studies of the Sun's outer atmosphere, where the radiation originates in the tenuous, high-temperature chromosphere and corona. Current levels of calibration accuracy of space instrumentation used to observe this radiation and accuracies desired in the future are discussed. Several suggestions are made for methods that can provide approximate recalibrations of instruments in orbit using the radiation from the Sun itself.

High rejection filters are difficult enough to achieve in the UV-VIS-IR with known materials and constants. Even more difficult is the design and manufacture of rejection filters in the EUV and VUV given the uncertainty of optical constants and their wide variation over this spectral range. We have begun work to characterize materials from 584 Å to 1,300 Å to verify reported optical constants, in order to design and realize the optimum collection system.

Modern large tokamak devices, with electron and ion temperatures in the range of 1 to 10 keV, plasma densities of 1 to 10 x 1013 cm-3, and quasistationary discharges of 1 to 10 s, emit copious amounts of soft x-ray and XUV radiation. Furthermore, plasma parameters such as temperatures, density, power input, and radiative power are usually well-characterized, making tokamak discharges extremely useful in experimental atomic physics and, to a lesser extent, instrumentation calibration.

For x-ray calibration of detectors used on laser created plasma experiments we have developed and characterized two kinds of sources : classical continuous x-ray sources operating at 1.8 keV and 5.4 keV and a pulsed source obtained by modifying a plasma Focus device. Calibration data for x-ray Charge - Coupled Devices (CCD) and photodiode linear array cameras are presented.