Radiometry by FTS in the visible and UV regions

Abstract

Much effort over many years has gone into evaluating and improving the wavenumber accuracy of FTS - the x-axis - but relatively little attention has been paid to the accuracy of the intensity measurements - the y-axis. This is particularly true of the UV region, where almost all spectrophotometry is done with grating instruments. We have used our high resolution UV FT spectrometer for making three different types of intensity measurements: branching ratios in emission, absorption cross-sections, and (at low resolution) lamp calibration. In the course of these measurements we have identified a number of sources of potential error, some known in advance and some discovered the hard way, some common to grating and FT spectrometers and some peculiar to FTS, and some that particularly affect the short wavelength region. This paper discusses the principal problems and the lessons we have learned. It also indicates some of the advantages (and the occasional disadvantage) that FTS has over grating spectrometry for radiometry in the UV.