Fourier transform infrared (FTIR) spectrometer has been widely used in spectral measurements, especially for transmission measurements of absorbing media, but most researchers assume that the internal light source is collimated, while it is convergent in fact. Therefore, it is necessary to explain the applicability of FTIR spectrometer in transmission measurements of absorbing materials. Based on this, influence of the deviation distance caused by the dispersion effect on the final detection is analyzed. Then expression of the deviation distance for single-layer absorbing media is first deduced, which is related to the convergent angle of incident beam, the refractive index and thickness of sample. The maximum measurable thicknesses of typical optical windows are calculated. Besides, influence of the random error in experiments on transmission measurements and radiation property identification of absorbing media are analyzed.

傅里叶变换红外（FTIR）光谱仪已广泛用于光谱测量，尤其是吸收介质的透射率测量，但是大多数研究人员认为内部光源是准直的，而实际上是会聚的。因此，有必要说明FTIR光谱仪在吸收材料的透射测量中的适用性。基于此，分析了由色散效应引起的偏离距离对最终检测的影响。然后，首先推导单层吸收介质的偏离距离的表达式，该距离与入射光束的会聚角，折射率和样品厚度有关。计算典型光学窗口的最大可测厚度。除了，