William R. Ott

Vacuum ultraviolet radiometry. 3: The argon mini-arc as a new secondary standard of spectral radiance

A miniature argon arc has been designed and tested as a new transfer standard of spectral radiance for the wavelength range from 114 nm to 330 nm. Calibration has been performed using two primary standard sources: the hydrogen arc from 130 nm to 330 nm and the blackbody line radiator from 114 nm to 130 nm. The mini-arc provides an intense, stable, and reproducible uv continuum with dc power requirements of less than 1.5 kW. The arc characteristics have been investigated, and the sensitivity of the radiant power output to various operating parameters has been measured. The rms uncertainty in the spectral radiance is estimated to be 5.3% above 140 nm and 10.1% between 114 nm and 140 nm, due primarily to uncertainties in the primary standard sources.

Spectral irradiance standard for the ultraviolet: the deuterium lamp

A set of deuterium lamps is calibrated as spectral irradiance standards in the 200-350-nm spectral region utilizing both a high accuracy tungsten spectral irradiance standard and a newly developed argon mini-arc spectral radiance standard. The method which enables a transfer from a spectral radiance to a spectral irradiance standard is described. The following characteristics of the deuterium lamp irradiance standard are determined: sensitivity to alignment; dependence on input power and solid angle; reproducibility; and stability. The absolute spectral radiance is also measured in the 167-330-nm region. Based upon these measurements, values of the spectral irradiance below 200 nm are obtained through extrapolation.

Vacuum ultraviolet radiometry with hydrogen arcs. 2: The high power arc as an absolute standard of spectral radiance from 124 nm to 360 nm

A wall-stabilized hydrogen arc can be utilized as a standard source of spectral radiance since the continuumemission coefficient is calculable to within a few percent. Previous efforts to apply this concept have been impeded by relatively large uncertainties associated with the plasma diagnostics. The present approach yields absolute intensities independent of other radiometric standards or the accuracy of any plasma diagnostics. The hydrogen arc is operated at high temperatures where the continuum emission coefficient reaches a broad, unique, and calculable maximum. Comparisons with other primary standards are consistent with the estimated uncertainty in the arc continuum intensities.

VUV Radiometry with Hydrogen Arcs. 1: Principle of the Method and Comparisons with Blackbody Calibrations from 1650 Å to 3600 Å

A method is described that utilizes the continuum emission from a wall-stabilized arc discharge as a radiometric standard in the vuv. Ultimately, this standard will cover the wavelength range from 500 A to 3600 A. Results of a first experiment comparing this method to two other calibration methods in the region above 1650 A are presented. A calibrated tungsten strip lamp is used between 2500 A and 3600 A the method of blackbody limited lines is applied at two wavelengths in the vuv. The hydrogen arc method depends upon the fact that the continuum emission coefficient for a hydrogen plasma at typical arc temperatures of about 14,000 K is calculable to within a few percent since the essential spectroscopic constants, continuum absorption coefficients, and transition probabilities are exactly known. The accuracy of the method depends primarily on the capability of spatially resolving in an end-on measurement the nearly homogeneous plasma layers near the axis of the cylindrically symmetric arc column.

Spectral radiance calibrations between 165-300 nm - An interlaboratory comparison

The spectral radiance of deuterium lamps calibrated by the Max-Planck-Institut fuer Astronomie (MPI), by the U.S. National Bureau of Standards (NBS), and by the Physikalisch-Technische Bundesanstalt (PTB) are compared to check the agreement of UV radiometric scales. The NBS group used the optically thin continuum radiation from a wall-stabilized hydrogen arc as its fundamental radiometric standard, while the MPI and PTB groups used the synchrotron radiation facility in DESY. It is found that the spectral radiance scales based upon the DESY synchrotron and the NBS hydrogen arc are consistent, at least for one wavelength relative to another.

Spectral-irradiance calibration of continuum emitted from rare-earth plasmas

The spectral irradiance of laser-produced plasmas of gadolinium and ytterbium have been determined in the 115-220-nm range for an incident 2.2-J, 30-nsec ruby-laser pulse. The effects of target geometry arnd variation of laser energy on the spectral irradiance were also studied. The potential of the source as a radiometric standard is discussed.

Vacuum-ultraviolet spectral-irradiance calibrations: method and applications

A method to determine the spectral irradiance of a radiation source in the vacuum ultraviolet through the use of recently developed spectral-radiance standards is described. The method has been applied between 138 and 310 nm, and the spectral irradiances of several different light sources have been measured on an absolute scale with estimated uncertainties less than 10%.

Monochromatic source of Lyman-α radiation

A source has been developed which produces a pure spectrum of Lyman-α radiation (1215.7 A). This source incorporates a wavelength selective filter and an rf-excited helium-filled lamp containing a mixture of uranium and uranium hydride in a sidearm. The uranium serves as a getter to eliminate atmospheric contaminants, and the uranium hydride, when heated, supplies H2 in a reproducible manner. The filter consists of a flowing-oxygen cell and a narrowband interference filter. The distinctive advantage of this device is that radiation in the VUV at a well-defined wavelength is obtained without the use of a monochromator. Characteristics of the source and measurements of the irradiance of the spectral line are given for a typical lamp. The irradiance and spectral purity are seen to be not strongly dependent on oxygen flow.

100 years of optical science and metrology at NIST

The National Bureau of Standards (NBS) was formed by Congress 100 years ago. The early Bureau was a small organization, founded at the beginning of the age of electricity to promote industrial productivity, commerce, technological progress, and the quality of life. It provided a basis for standardizing the measurements and products that are so important to a nations infrastructure. The original staff numbered 12. There were 15 offices and laboratories. Five areas of optics have been important elements of the Bureaus research for almost its entire history: atomic and molecular spectroscopy; radiometry; colorimetry; optical properties of materials; and, for the last 40 years, laser science and applications. Research and measurement services have supported national programs ranging from the manufacture of high quality optical glass during two World Wars to the calibration of spectrometers on the Hubble Space Telescope. Pioneers in optical science and metrology at NBS/NIST include many well known scientists, ranging from William Coblentz, who established the field of optical radiometry during his 40 year career from 1905-1945, to William Phillips, who received the Nobel Prize in Physics in 1997 for his research on the laser cooling and trapping of atoms.