General design method for ultralong optical path length multipass matrix cells.

Abstract

For what we believe to be the first time, we propose a general design method for ultralong optical path length (OPL) multipass matrix cells (MMCs) based on the multicycle mode of two-sided field mirrors. Based on the classical Pickett Bradley White cell (PBWC), the design idea of the dual-circulation mode based on two-sided field mirrors is described in detail, with the example of the MMC based on the PBWC-PBWC. Its simple design method and optical stability analysis are given. The other three MMCs based on the dual-circulation mode using the PBWC and Bernstein Herzberg White cell (BHWC) are given. Furthermore, we propose a general design method for ultralong OPL MMCs with multicycle mode by adding cyclic elements. The OPL of the MMCs designed via this method can reach the order of kilometers or even tens of kilometers. To verify the effectiveness of the design method, a CH₄ detection system with an MMC based on PBWC-PBWC-PBWC was constructed. The OPL of the MMC is 1,138 m. Allan deviation analysis reveals that the minimum detection limit of methane is 367 ppt. The design method proposed in this paper provides a new idea for the design of multipass cells (MPCs), and the new MMCs have great potential application value in the field of high-precision trace gas monitoring.