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Silicon n-on-p photodiodes with 100 % internal quantum efficiency have been studied in the 160 nm to 254 nm spectral range. Preliminary values have been determined for the quantum yield of silicon at these wavelengths. Using these values, a trap detector is presented for absolute flux measurement in this region. The stability under intense 193 nm irradiation, a property of importance in lithography and in photorefractive keratectomy, has been measured, and the diodes tested were found to be several orders of magnitude more stable than p-on-n diodes tested by other investigators at this wavelength. Spatial nonuniformities of the n-on-p diodes were found to be less than 1 % at wavelengths of 254 nm and 161 nm.

The solar soft X-ray (XUV) radiation is highly variable on both short-term time scales of minutes to hours due to flares and long-term time scales of months to years due to solar cycle variations. Because of the smaller X-ray cross sections, the solar XUV radiation penetrates deeper than the extreme ultraviolet (EUV) wavelengths and thus influences the photochemistry and ionization in the mesosphere and lower thermosphere. The XUV Photometer System (XPS) aboard the Solar Radiation and Climate Experiment (SORCE) is a set of photometers to measure the solar XUV irradiance shortward of 34 nm and the bright hydrogen emission at 121.6 nm. Each photometer has a spectral bandpass of about 7 nm, and the XPS measurements have an accuracy of about 20%. The XPS pre-flight calibrations include electronics gain and linearity calibrations in the laboratory over its operating temperature range, field of view relative maps, and responsivity calibrations using the Synchrotron Ultraviolet Radiation Facility (SURF) at the National Institute of Standards and Technology (NIST). The XPS in-flight calibrations include redundant channels used weekly and underflight rocket measurements from the NASA Thermosphere-Ionosphere-Mesosphere-EnergeticsDynamics (TIMED) program. The SORCE XPS measurements have been validated with the TIMED XPS measurements. The comparisons to solar EUV models indicate differences by as much as a factor of 4 for some of the models, thus SORCE XPS measurements could be used to improve these models.

Evaluation of five types of silicon photodiode was undertaken to verify their suitability for absolute radiometry and also for their use as transfer standards in the spectral region from 1 nm to 1100 nm. Four types of photodiode were fabricated for this study; these were the p-on-n photodiode, n-on-p photodiodes with silicon dioxide front windows and n-on-p photodiodes with a metal-silicide front window. Fabrication of photodiodes with 100% internal quantum efficiency is demonstrated and their necessity for making absolute radiometric measurements with the lowest possible uncertainty is pointed out. The linearity characteristics of these devices, as measured by the ac/dc method, are far superior to those of the p-on-n diodes especially fabricated for this work and also to those exhibited by p-on-n diodes widely used at present by the radiometric community. Results on the stability of the quantum efficiency of the fabricated diodes after exposure to intense radiation of 13 nm, 120 nm, 157 nm, 193 nm and 254 nm radiation will also be presented. Photodiodes with a metal-silicide front window were the only devices stable when exposed to the intense beams of third-generation synchrotrons and UV excimer lasers.

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The recently completed upgrade of the Synchrotron Ultraviolet Radiation Facility ͑SURF III͒ at the National Institute of Standards and Technology ͑NIST͒ has improved the accuracy of radiometric measurements over a broad spectral range from the infrared to the soft x ray. The beamline 4 at SURF III is a cryogenic-radiometer based radiometric facility for the ultraviolet ͑UV͒ spectral range. The upgrade of SURF III has allowed us to use beamline 4 to improve the detector spectral power responsivity scales in the wavelength range from 125 to 320 nm. The achieved combined relative standard uncertainty is better than 0.5% over most of this spectral range. This is a significant improvement over the more than 6% relative standard uncertainty in this spectral range of the current scales maintained at the Spectral Comparator Facility ͑SCF͒ in the Optical Technology Division and the Far UV Calibration Facility in the Electron and Optical Physics Division. The new UV scale of beamline 4 was subsequently intercompared and transferred to the SCF and to the Far UV Calibration Facility to improve their UV scales and ensure consistency within NIST. The new scale established at beamline 4 improves NIST's calibration capabilities for environmental monitoring, astrophysics, and the UV industry. The new scale also includes wavelengths such as 193 and 157 nm excimer laser wavelengths, which are of particular interest to the semiconductor photolithography industry.