Diffraction and Line Shape of Fourier-Transform Spectrometers

The effect of diffraction on the instrument line shape of a Fourier-transform spectrometer is studied with an analytical line-shape model. The expression for the instrument line shape of a diffracted point source is obtained. A simple condition on the throughput of the instrument is derived under which diffraction is negligible when compared with the field-of-view-induced line shape. The effect of diffraction is illustrated and compared for various instruments.