Thermocouple Measurements of Spectral Intensities in the Vacuum Ultraviolet*

Abstract

The spectral energy distribution of the radiation from a high intensity hydrogen arc, after dispersal by a vacuum monochromator, was measured with a thermocouple in the spectral region 2600 to 900A. An aluminized one-meter concave grating, having a dispersion of 17A/mm, was used near normal incidence in the first-order spectrum. A thermocouple sensitivity of 1.6 μv/μw was adequate for recording most of the spectrum at a band width of 14A. Arrangement of equipment rendered unnecessary the use of windows in front of the thermocouple and end-on hydrogen arc. Spectral energies in the many-lined molecular spectrum below 1700A were 5 to 40 times those found in the continuum above 1700A. The results show that it is now possible to extend the range of various energy detectors, calibrated in absolute response, throughout the vacuum ultraviolet down to 900A.