John M. Bridges

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.

Investigation of a laser-produced plasma VUV light source.

An investigation was conducted on the VUV radiation from laser-produced plasmas using a channel electron multiplier detector and a 1.5-m grazing incidence spectrometer. High-resolution quantitative spectra from 8 to 40 nm were obtained from the plasmas generated by a 0.5-J Nd:YAG laser focused on nine different target materials. The effects on the plasma emission of laser energy and focus were measured.

Irradiances of spectral lines in mercury pencil lamps.

The irradiancesof 37 spectral lines emitted bymercury pencil-type lamps were measuredby comparison with calibrated continuum sources. The lines span the region 230-590 nm. For the 14 most prominent lines the absolute irradiances should be useful for radiometric calibrations at an uncertainty level of ~15% 195% confidence2. The ratios of the irradiances for this same group of lines are significantly more reproducible; they should be useful at an uncertainty level of ~10%.

Characterization of argon arc source in the infrared

A wall-stabilized arc source is being investigated as a radiometric source for the near- and mid-infrared spectral range. This arc is similar to the argon mini-arc, which has been used as a radiometric source in the ultraviolet. The potential usefulness of the arc in the infrared (IR) range stems from its high brightness in this region. The arc has been tested as a source for a recently constructed facility for calibrating IR detectors. Over the range 3 ?m to 11 ?m, the signals with this source were greater by a factor of 6 to 17 than the signals from a 1500 K ceramic element, despite the beam from the arc being smaller in angular extent. The radiance of the source was calibrated from 1,6 ?m to 10,6 ?m via a 1140 K black body. Over most of this spectral range the radiance of the arc is equal to that of black bodies ranging in temperature from 5000 K to 10000 K. From 1 ?m to 3 ?m, a spectral scan with relatively high resolution shows a spectrum dominated by strong Ar I line emission. Finally, measurements were made of radiance as a function of arc current and translational position of the source.

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%.

Transition Probabilities for Prominent Ar i Lines in the Near Infrared

Relative transition probabilities of 81 infrared Ar i lines in the wavelength range from 9000–24 000 A have been measured with a wall-stabilized arc operating in argon at atmospheric pressure. The large majority of the lines from the 4p–5s and 4p–3d transition arrays has been observed and the measurements are consistent with the J-file-sum rule. The data have been normalized to an absolute scale by utilizing the results of other recent arc and lifetime experiments.

High-resolution VUV spectrometer with multichannel detector for absorption studies of transient species

A new high-resolution VUV spectrometer is demonstrated for applications in the 40–900-A wavelength range. The instrument is comprised of a laser-plasma VUV source, which provides continuum background illumination, 1.5-m grazing incidence spectrometer, and a 1024-channel VUV optical multichannel analyzer (VUV-OMA). The VUV-OMA is of new design, featuring a special resolution enhanced channel electron multiplier array in an overall configuration chosen to optimize the spatial resolution of the detector while maintaining single-photoelectron sensitivity.