Fitting method for vacuum ultraviolet spectrometer calibration using line ratio technique

We have developed theoretically a generalized least squared fitting, using as fitting function the exponential of a cubic polynomial, and as data, the efficiency ratios between different wavelengths in the vacuum ultraviolet spectral range. The fitting function is suggested by the linear interpolation of efficiency ratios whose wavelengths are nearby. We have tested the fitting proposed for data given by different authors in the literature, obtaining a determination coefficient above 98%.