Measurement of Fourier transform infrared spectrometer instrument lineshape

摘要

Abstract: This work describes the use of a He:Ne laser based test rig, developed at NPL, and a low pressure gas cell containing CO to measure the instrument line shape (ILS) function of a Unicam Research Series FTIR spectrometer, which has been extensively used for the detection and measurement of fugitive gas emissions. During the ILS function measurements minor optical misalignments were introduced into the optical system, and their effect on the measured ILS function observed. The ILS functions obtained using the laser system and low pressure gas cell containing CO were in good agreement, both having a full width at half maximum of 0.3 cm$+$MIN@1$/. The minor optical misalignments had a significant effect on the ILS function. The initially symmetric function became more asymmetric as the degree of misalignment was increased. Gas concentrations have been retrieved using a symmetric and an asymmetric ILS function, and the differences presented. !6