CALIBRATION OF VUV SPECTROMETER-DETECTOR SYSTEM USING SYNCHROTRON RADIATION.

A new technique and apparatus have been developed for the measurement of absolute electron impact photoemission cross sections in the 30-150-nm wavelength range. Synchrotron light is used as the primary intensity standard for the calibration of the detection efficiency of a vacuum ultraviolet (VUV) spectrometer-detector system. A multiadjustable manipulator was used to position precisely a Seya-Namioka-type spectrometer-detector system with respect to a narrow ray of synchrotron radiation. By scanning the beam of synchrotron radiation across the surface of the grating in the spectrometer, precise simulation of the geometry of the light source encountered in the electron impact photoemission mesurement was realized. Analysis of the results underscores the fact that for spectrometer calibrations in the VUV, the calibration procedure depends on the geometry of the experimental source. The simultaneous determination of the absolute apparatus response function of the spectrometer-detector system and the geometrical factors pertaining to the electron impact photoemission source allows photoemission cross sections in the VUV to be determined with unparalleled precision.