Advantageous Apodization Functions for Absorption-Mode Fourier Transform Spectroscopy

Abstract

A systematic examination of the efficacy of window functions for reduction of the spectral skirt of absorption-mode Fourier transform spectra is reported. A window which has its maximum at the beginning and its minimum at the end of the time-domain data gives a satisfactory absorption line shape. In contrast, a symmetrical window with its minima at the ends and its maximum in the middle gives an unsatisfactory absorption line shape. These symmetrical windows are satisfactory for apodization of magnitude spectra. The efficacy for reducing the spectral skirt is examined for the general case of a damped time-domain signal, with specific cases ranging from undamped to essentially completely damped signals. The choice of the window is dependent upon the required dynamic range and the amount of damping in the time-domain data. For a dynamic range of 100:1, the Noest-Kort absorption window and the Norton-Beer F3 windows are the windows of choice. For a dynamic range of 1000:1, either the Filler E0.20 window or the Kaiser-Bessel window can be recommended. The sensitivity change accruing from windowing is reported for all windows examined, for a damping range from zero to essentially complete damping