Spot pattern optimization of a dense multi-pass cell using a quasi-variance analysis method

To design a dense multi-pass cell (MPC) with optimized spot pattern, a quasi-variance analysis method is proposed and by which the MPC’s spot deformation is investigated. We put forward a design scheme of a dense double spherical coaxial mirror MPC with optimized spot pattern. By using the ABCD transmission matrix without paraxial approximation, a calculated spot pattern which is very close to the actual spot distribution is obtained. The shape of the spot is analyzed by the discrete Gaussian multi-ray calculation model. First discovered the incident position and incident angle has a huge impact on the shape of the spot, and a quasi-variance (σ value) analysis method was proposed to quantitatively evaluate the spot deformation of the dense MPC. By using the quasi-variance analysis method, an optimized eight-ring spot pattern was achieved and verified experimentally for a dense double spherical coaxial mirror MPC when the incidence position is r=17 and the incidence angle is (5.5, 6.9). The dense MPC with eight-ring spot pattern was with an optical path length of 10 m and a σ value of 0.2176. •A quasi-variance analysis method for evaluating the MPC’s spot deformation is proposed.•The incident position and angle greatly affect the spot shape.•An optimized eight-ring spot pattern is obtained by the quasi-variance analysis method.