衍射光栅光谱仪和法布里珀罗(FP)干涉仪是两类非常典型和重要的光谱仪器。从波动光学的角度看, 光栅衍射和FP干涉都可看成是多波列的相干叠加。由于波列之间存在光程差, 光的相干长度限制着同时参与相干叠加的最大波列数。针对现有理论将光栅衍射和FP干涉同时参与相干叠加的最大波列数分别定为透光狭缝总数和无穷大的情况, 分别引入有效透光狭缝数和有效透射光光束数来说明光的相干长度对衍射光栅光谱仪和FP干涉仪这两类光谱仪器分辨本领的影响。

Diffraction grating spectrometer and Fabry-Perot(F-P) interferometer are two kinds of typical and important spectral apparatus.From the viewpoint of wave optics, grating diffraction and F-P interference both can be regarded as coherent superposition of multiple-wave train.Coherence length of light limits the maximal number of coherently-superposed wave trains at the same time, because of the existence of optical path difference between the wave trains.Due to the situation which the theory unconditionally sets the maximal number of coherently-superposed wave trains at the same time equals to the total number of transmitting slits and infinity respectively for grating diffraction and F-P interference, effective number of transmitting slits and effective number of transmitted beams are introduced to illustrate the influence of coherence length on resolving power of the two kinds of spectral apparatus.