INTENDED OUTCOME AND BACKGROUND

The objective of this strategic element is to critically compile fundamental constants and atomic spectroscopy data from the far infrared to the x-ray regions. We disseminate these reference data on the Physics Laboratory website, produce high-quality data for urgent scientific or technological needs, and resolve discrepancies in the body of the data.

The NIST databases for atomic spectra and fundamental constants are recognized throughout the world. The Atomic Spectroscopic Database on our website now receives about 80,000 downloads per month, up from 60,000 only two years ago. The principal users are plasma physicists, crystallographers, astronomers, lighting engineers, and spectrochemists.

However, the databases are still far from complete, and the quality of the data available in the literature from which the databases are built is uneven. The current versions of our databases are not sufficiently reliable for some fields of science and technology, and needs for such reference data are continuously growing. Our scientists focus their resources on the most urgent needs of the user communities. When accurate, reliable data do not exist for high priority needs, specific measurements or calculations are undertaken to produce them.

Accomplishments

• New X-Ray Wavelength Table in Review of Modern Physics

  Important experimental and theoretical developments in the field of x-ray transitions have made the mid-1960s database of these transitions obsolete. On the experimental side, x-ray wavelengths can now be more accurately linked to optical wavelengths and the SI definition of length, through combined x-ray and optical interferometry. In addition, a number of recent, accurate x-ray measurements, and updated values of the fundamental physical constants, are available to be included in the database. On the theoretical side, there has been continued development of better calculational procedures that produce results in excellent agreement with experiment. This good agreement creates the possibility that theoretical values can provide rather good estimates of missing or poorly measured experimental data.

  In collaboration with theorists in France and Sweden, we have produced a new reference x-ray wavelength table that is being published in Reviews of Modern Physics. The new table is the culmination of a long-term NIST effort to produce an improved, comprehensive data resource for x-ray transition energies. It contains K- and L- x-ray transition and absorption edge energies for all elements from neon to fermium. It includes carefully selected and evaluated experimental data robustly connected to the SI definition of length, and accurate, state-of-the-art theoretical estimates. The new x-ray wavelength table will soon be available also on the NIST Physics Laboratory website.

  CONTACT: Dr. Ernest Kessler (301) 975-4844 ernest.kessler@nist.gov

  
  
  

• Handbook of Basic Atomic Spectroscopic Data

  To meet increasing needs for reference spectral data for neutral and singly-ionized atoms, we completed a new database of wavelengths, energy levels, and transition probabilities for the most important transitions in all elements from hydrogen to einsteinium.

  This Handbook of Basic Atomic Spectroscopic Data lists wavelengths and intensities for over 12,000 transitions. Energy levels and transition probabilities are given for about 2400 of the strongest lines, taken from over 400 references. Data for individual elements can be accessed by name, atomic number, or atomic symbol. A finding list is available to assist in identification of possible impurities in an observed spectrum.

  This handbook will be published in standard paper format, in an e-book that combines ease of use and portability, and in an electronic version on the Physics Laboratory website.

  CONTACT: Dr. Jean Sansonetti (301) 975-4725 jean.sansonetti@nist.gov

  
  
  

• Precision Measurement of Laser Wavelengths for 157 nm Microlithography

  The next generation of microlithography tools will be based on a molecular-fluorine laser operating at 157 nm. In order to design optical systems for focusing ultraviolet radiation from the laser onto the chip substrate, the index of refraction of the optical materials must be known to high accuracy. Since the index of refraction varies rapidly with wavelength, it is critical that the wavelength of the laser also be accurately known.

  To obtain accurate wavelengths for the F₂ laser, we used the NIST 10 m vacuum spectrometer to measure the lasing lines from a commercial F₂ laser in the region of 157 nm. The experiment was conducted in collaboration with an excimer laser manufacturer, which supplied the laser. The spectra were calibrated by spectral lines from a platinum hollow-cathode lamp that had been measured by NIST and used to calibrate spectrometers on the Hubble Space Telescope. The high accuracy of these measurements relied on a specially designed system to illuminate the spectrometer in such a way as to eliminate small shifts between the spectrum of the lasing lines and that of the calibration lamp.

  Wavelengths of six lasing lines were measured to an uncertainty of ± .0001 nm. Three of the lines were newly observed lasing lines.

  CONTACT: Dr. Craig Sansonetti (301) 975-3223 craig.sansonetti@nist.gov

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"Technical Activities 2002" - Table of Contents