Vacuum Ultraviolet And Extreme Ultraviolet Radiometry Using Synchrotron Radiation At The National Bureau Of Standards

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Abstract
Synchrotron radiation is a source of continuum radiation ranging from the x-ray or soft x-ray region (depending on machine energy) to beyond the visible region. The amount of radiation emitted is a calculable function of machine operating parameters. This makes it possible to use synchrotron radiation from electron synchrotrons and electron storage rings as an absolute source particularly in the vacuum ultraviolet (VUV) and soft x-ray regions where other standards are difficult to find. At the National Bureau of Standards (NBS), an electron storage ring (SURF-II) has been used to calibrate spectrometers and photometers used in solar and aeronomy research and in fusion plasma diagnostics. A large chamber has recently been completed to facilitate such calibrations. The radiation incident on these spectrometers can be calculated to uncertainties of 3%. A technique to exactly determine the number of electrons orbiting in the ring is currently being developed to reduce this uncertainty. Detector calibrations between 5 to 55 nm (50 to 550 A) are routinely carried out at SURF-II, and transfer standard detec-tors with 6 to 10% uncertainties over the range of 5 to 254 nm (50 to 2540 A) are supplied. Special studies of "practical," high efficiency, and disposable photodiodes have been made by NBS in collaboration with other groups.

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