Small changes in mirror displacement cause variations in the reflection pattern and corresponding optical path length in a multi-pass absorption cell. Herein, we propose a path length calibration-free laser absorption spectrometer based on a frequency modulated continuous wave (FMCW) ranging system. The absorption coefficient of atmospheric oxygen and the optical path length in a multi-pass absorption cell were measured using direct absorption spectroscopy and an FMCW ranging system, respectively. Further, the measured optical path length in the multi-pass absorption cell was compared with ray-tracing simulations. In addition, we demonstrated that the optical absorption coefficients measured by the direct absorption spectroscopy were not affected by changes in the distance between mirrors.

反射镜位移的微小变化会导致多通道吸收池中反射模式和相应光路长度的变化。在此，我们提出了一种基于调频连续波 (FMCW) 测距系统的光程免校准激光吸收光谱仪。分别使用直接吸收光谱和 FMCW 测距系统测量大气氧的吸收系数和多通道吸收池中的光路长度。此外，将多通道吸收池中测得的光程长度与光线追踪模拟进行了比较。此外，我们证明了通过直接吸收光谱测量的光吸收系数不受镜子之间距离变化的影响。