According to the basic principle of the Herriott-type multi-pass cell (MPC), this paper analyzes the relationship between the optical path length (OPL) and the distance of the mirrors, and proposes a design method of variable optical path length MPC, which makes it easier to implement variable optical path length MPC. In the design, the incident angle is controlled to arrange the spots in a circle on the concave mirrors, and a method of adjusting the distance between the reflectors and the position of the exit point is proposed to realize the continuous and controllable numbers of passes (integer). MPC is frequently used to improve the sensitivity of gas detection, and the variable OPL designation is helpful for gas detecting of wide concentration range and the exploration of noise compensation methods in MPC.

根据Herriott型多通道像元（MPC）的基本原理，分析了光程长度（OPL）与反射镜距离之间的关系，提出了可变光程长度MPC的设计方法，这使得实现可变光程长度MPC更容易。在设计中，控制入射角以在凹面镜上将光斑排列成圆形，并提出了一种调整反射镜之间的距离和出射点位置的方法，以实现连续且可控制的通过次数（整数）。MPC通常用于提高气体检测的灵敏度，而变量OPL的名称有助于在宽浓度范围内进行气体检测以及探索MPC中的噪声补偿方法。