Lanny R. Hughey

SURF's up at NBS: A Progress Report

The NBS Synchrotron UV Radiation Facility (SURF-II) is a 250 MeV single-magnet, weak-focusing electron storage ring, with 10 MeV microtron injector. Circulating beams of up to 35 mA at energies up to 250 MeV have been achieved. Beam lifetime, limited by Touschek effect, is extended to several hours by resonant vertical rf excitation. At low energies bunch shape oscillations occur, involving coherent synchrotron oscillations, negative-mass-type blowup and loss of beam. Effective avoidance and suppression techniques are discussed. A new set of high current gradient correction coils and power supplies, plus additional pancakes for the main field coils are being obtained. These are expected to extend SURF operation to 280 MeV and provide useful light output to 0.4 keV photon energies.

Comparison of the NBS SURF and tungsten ultraviolet irradiance standards

Detailed comparisons of the spectral irradiance of the NBS Synchrotron Ultraviolet Radiation Facility II and tungsten FEL Scale of Spectral Irradiance at 297 and 254 nm with an uncertainty of ~1% show that these irradiance standards are consistent at both wavelengths to within the uncertainties assigned to them by NBS.

Polarization characteristics of silicon photodiodes and their dependence on oxide thickness

We have studied the polarization dependence of silicon photodiode responsivity as a function of wavelength, the angle of incidence, and the thickness of the silicon dioxide overlayer. The experimental results in the spectral region where there is no absorption in the silicon dioxide are explained well by a purely optical model. The responsivity dependence on polarization in the VUV is found to be smaller than that predicted and to be explainable by the presence of charge injection from the silicon dioxide layer.

Improved resolution and flexibility of the SURF II high-throughput 2-m normal-incidence monochromator

Abstract This paper describes the new optical and vacuum systems designed for coupling the SURF II high-throughput 2-m normal-incidence monochromator to the SURF II storage ring at the National Institute of Standards and Technology. This new system preserves the high output flux of the old configuration and extends the range of both wavelength resolution and sample chamber pressure limits. The new beamline has a toroidal mirror, a plane mirror, an externally-adjustable entrance slit and additional vacuum pumping.

Comparison of the NIST SURF and argon miniarc irradiance standards at 214 nm.

Comparison of NISTs SURF-II primary irradiance standard and argon miniarc irradiance standard at 214 nm with an uncertainty of ~3% shows that at this wavelength these irradiance standards agree to within the uncertainties of 1.3 and 7%, respectively, assigned to them by NIST.

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.

The very high resolution spectrometer at the National Institute of Standards and Technology

Abstract The Very High Resolution Spectrometer at the Synchrotron Ultraviolet Radiation Facility of the National Institute of Standards and Technology has been upgraded with improved beamline throughput, instrument control and data acquisition. Since this upgrade, a number of high resolution measurements have been made in the vacuum ultraviolet region of the electromagnetic spectrum between 40 nm and 100 nm. Utilizing the features of this instrument, on-line photoelectric recording at intervals of 0.1 pm in first order from a synchrotron light source can be made. A resolution of 0.9 pm has been obtained at 80 nm.

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...

SURF II: Characteristics, facilities, and plans

This facility report describes the Synchrotron Ultraviolet Radiation Facility (SURF II) operated by the National Institute of Standards and Technology, Gaithersburg, Maryland. SURF II is a 300‐MeV electron storage ring which provides well characterized continuum radiation from the far infrared to the soft x‐ray region with the critical wavelength at 17.4 nm. Brief descriptions are given of the user facilities, the characteristics of the synchrotron radiation, the main storage ring, the injector system and each of the operating beam lines, and associated instruments. Further description is given of expansion plans for additional beam lines.