R. P. Madden

NBS Detector Standards for the Far Ultraviolet

A program at NBS leading to the realization of practical, stable transfer detector standards for the far ultraviolet is reviewed. Three basic detector types, one covering the region of 584-1216 A and the other two covering the region of 1164-2537 A, are described. Examples of these detectors have been calibrated at NBS and distributed to laboratories throughout the United States and Europe, where they are being used as primary radiometric calibration references in a variety of far-uv experiments.

New Reference Spectrophotometer

A new single beam spectrophotometer is described in which transmittance is measured by placing samples normal to a parallel beam of light. Collimation and focusing of the main beam are achieved by means of off-axis parabolic mirrors. The wavelength at which the transmittance is to be measured is selected by a plane grating monochromator having off-axis parabolic mirrors and circular holes as entrance and exit apertures. The instrument has an inherent accuracy estimated to be 0.0001 transmittance unit. Its precision is characterized by a repeatability of 0.00004 transmittance units for neutral-density filters with transmittances between 10% and 30%. The design philosophy used to achieve these results is presented. A discussion of some systematic errors commonly neglected in routine spectrophotometric, measurements is given. Systematic errors such as detector nonlinearity and stray radiant energy are measured.

Synchrotron ultraviolet radiation facility (SURF II) radiometric instrumentation calibration facility

Spectrometer calibrations have been performed at the National Institute of Standards and Technology (formerly the National Bureau of Standards) for over 10 yr using the calculable synchrotron radiation from the SURF II electron storage ring. SURF II is now a high-performance storage ring that can operate at electron energies up to 300 MeV and with over 250 mA of stored current. One beam line, operationally supported by the National Aeronautics and Space Administration (NASA), is dedicated for use as a radiometric instrumentation calibration facility for outside users.

A status report on the SURF II synchrotron radiation facility at NBS

Abstract Recent work to upgrade the SURF II (Sychrotron Ultraviolet Radiation Facility) storage ring is described, resulting in reliable operation up to 252 MeV at currents in the range 10–20 mA. A wide variety of experiments is now in progress at the facility, encompassing solid state physics, atomic and molecular physics and molecular biology, as well as the all-important radiometric standards work. The instrumentation used for these experiments is described; brief details of the experiments themeselves are also given.

Dual grating monochromator for detector calibrations using synchrotron radiation as an absolute source at NIST

Abstract A new monochromator system has been developed that permits the in situ calibration of its optical components and allows the calibration of a photodiode against a calculable synchrotron radiation source in the spectral range extending from 116 to 254 nm. The instrument has been operated at the Spectrometer Calibration Facility (BL-2) of the SURF II electron storage ring located at the National Institute of Standards and Technology (NIST). Significant reductions in the uncertainty of far ultraviolet detector calibrations are anticipated due to the use of this instrument.

Resonance phenomena in molecular photoionization: impact of synchrotron radiation

The nature of resonance phenomena in atomic and molecular systems is reviewed along with a discussion of the utilization of synchrotron radiation in studying resonance phenomena. The effects of autoionization and shape resonances on the branching ratios and asymmetry parameters for several systems are discussed. The potential and current status of threshold photoelectron spectroscopy and ion coincidence techniques are discussed.

Comparison of an Ionization Chamber and a Thermopile as Absolute Detectors in the Extreme Ultraviolet

A comparison has been made between a calibrated thermopile and an argon ionization chamber as absolute detectors of radiant flux of wavelengths 584 A and 735 A. Corrections were applied to the data in order to account for the absorption due to gases in the monochromator, the energy carried away from the thermopile by photoejected electrons, nonuniformity of response across the surface of the thermopile, and uneven illumination of the thermopile by the flux from the monochromator. The two detectors were found to agree within the 3% estimated probable error in the measurements.

NIST programs for calibrations in the far ultraviolet spectral region

The National Institute of Standards and Technology (NIST) serves the growing ultraviolet user community by providing calibration services throughout the spectral range from 2 nm to 400 nm. In this paper we describe the far ultraviolet transfer standard detector program, the NASA-supported Spectrometer Calibration Beamline at the Synchrotron Ultraviolet Radiation Facility, SURF III, and the recent upgrade of the SURF electron storage ring. Several types of transfer standard detectors are issued by NIST in the spectral range from 5 nm to 254 nm; Al2O3 windowless photoemissive devices, CsTe photoemissive devices with integrated MgF2 windows, and radiation-hardened, semiconductive Si photodiodes. The Spectrometer Calibration Beamline makes use of the cathode, undispersed synchrotron radiation from SURF III as a standard of spectral irradiance from 2 nm to 400 nm. The upgrade of SURF has greatly improved the accuracy of calibrations based on SURF, as well as extending the useful spectral range to shorter wavelengths. Taken together, the transfer standard detector program and the calibration beamline at SURF III offer a unique calibration resource for scientists and engineers working in the far ultraviolet spectral region.

XUV radiometric standards at NBS

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 users 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.

SURF III - A New Electron Storage Ring at NIST

The National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS), has operated the Synchrotron Ultraviolet Radiation Facility (SURF), based on an electron accelerator, continuously since the early 1960s. SURF I was established in 1961, utilizing a 180 MeV electron synchrotron at NBS in Washington, D.C. This accelerator was moved to the Gaithersburg, MD site in 1968, specifically for the continuation of SURF I operations. It was converted to an electron storage ring, SURF II, in 1974 under contract with the Physical Sciences Laboratory (PSL) at the University of Wisconsin-Madison (UW), and became a national standard of irradiance in the UV and VUV spectral region. To improve its performance in this application and broaden its spectral range, SURF II has been converted to SURF III, commissioned in December 1998. The design and construction of the new system were overseen by PSL and the Synchrotron Radiation Center at UW. SURF III remains a weak-focusing, single-magn...