Uncertainty Consideration in Sampling for High Resolution Fourier Transform Spectroscopy

The use of dispersive Fourier transform techniques in interferometry allows the measurement of absorption coefficient and refractive index spectra with great precision. Normally, the sharp rotational lines of gaseous molecules can be resolved once higher resolution spectroscopy is employed. The high resolution requires recording of interferogram data points over an extended mirror movement. The issue of sampling size was never considered in the past. This paper presents the importance of using precise step motors for data sampling in these highly sensitive measurements. In order to assess rotational lines of pollutant gases, precise step motors are required to obtain the absorption and refractive index spectra at different pressures, giving insight into the behavior of the spectral lines with varying parameters. Our measurements demonstrate for the first time that changing the sampling size greatly affects the highly sensitive output of the finely tuned high resolution Fourier transform spectrometer. This paper examines the data sampling results obtained by using two different step motors; one very fine step motor and another slightly coarser step motor. This is critical in high resolution spectroscopy studies as coarser sampling size can greatly deteriorate the phase as well as amplitude information which leads to significant changes in final absorption and refractive index data.