Generalized design of a zero-geometric-loss, astigmatism-free, modified four-objective multipass matrix system

Symmetric optical multipass matrix systems and the general rapid design methodology

We proposed an original type of multipass cell named symmetric optical multipass matrix system (SMMS), in which the same matrix patterns of various sizes can be formed on both sides. According to its special symmetric configurations, the SMMS design problem is modeled as a variant of the classical traveling salesman problem, which can be rapidly solved by evolutionary optimization algorithms. Two sets of 3-mirror SMMSs are designed, analyzed and built, which show superior characteristics of high stability, desirable beam quality and adjustable optical path lengths. Additionally, they can support simultaneous detection of multiple species with multi-laser channels. The proposed method is further extended to design a 4-mirror SMMS, which verifies the universality and robustness of the design methodology. The experimental observations are in consistent with the theoretical calculations. The newly proposed SMMSs have a broad application prospect in trace gas measurement.

Generalized design of simple, stable and compact nested multipass cells with a reentrant symmetric concentric circle pattern

We present a particular solution of the Herriott design by replacing each spherical mirror with two coaxial nested spherical mirrors with different curvatures. The analytical solution of the nested MPC parameters is derived based on the principle of the Herriott cell and the symmetry of the pattern, which enables the rapid design of nested MPCs with different optical path lengths (OPLs). The nested MPC performance is explored by parameter analysis, the ray tracing method and the transfer matrix method. We further designed and manufactured a miniaturized and long-OPL MPC, which exhibits robustness, high mirror utilization and a good q-parameter of the output beam. The miniaturized nested MPC can achieve a 10 m effective OPL at a volume of 28.4 mL, and the long-OPL MPC can obtain a 100 m effective OPL at a volume of 1.3 L.

Optical design and analysis of a two-spherical-mirror-based multipass cell

A systematic method for the optical design and analysis of a multipass cell (MPC) with two spherical mirrors is presented. By varying the parameters, including the distance between the mirrors, the position of the incident point, and the incident angles, a variety of dense patterns can be formed on the mirrors. Three MPCs with exemplary patterns of seven circles, rotating triangles, and petals are designed and built. We compare and analyze the parameters of each MPC with respect to the volume, the optical path length (OPL), the number of reflections, and the stability of the final spot position. This new type of MPC exhibits the superior characteristics of compactness, a long effective OPL, and affordable cost, which make it very suitable for applications to trace gas sensing.

Generalized method for seeking q-preserving configurations of multi-pass cells

A method is presented for seeking specified multi-pass cell (MPC) configurations with q-parameters of the input and output Gaussian beams that remain the same (q-preserving configurations). The Frobenius norm (F-norm) is chosen as the quantitative criterion of the deviation between the transfer matrix of the MPC configurations and identity matrix. When the deviation is down near to zero, the corresponding configuration is close to an ideal q-preserving configuration. In contrast to common 2 × 2 transfer matrixes that are only applicable to MPCs with negligible astigmatism, we adopt 4 × 4 transfer matrixes that are also workable for multi-pass systems with astigmatism. To demonstrate the validation of the method, several q-preserving structures of four-objective multi-pass matrix system (FO-MMS) and double-row circular MPC (DR-CMPC), which are two fundamentally different MPC types, are illustrated. The variation tendencies of the quantitative deviation between the transfer matrix and the identity matrix are discussed in detail for each structure as functions of structural parameters. The optimal q-preserving structures are found for FO-MMS and DR-CMPC, with the matrix deviation of 0.0047 and 0.0051, while the corresponding total optical path length (OPL) are 33.6 m and 67.8 m, respectively. The OPL of the optimal DR-CPMC is longer than the traditional CMPC in the state of the art, and the deviation is three orders of magnitude smaller if the similar spherical reflecting surfaces are adopted.

Generalized Optical Design of the Double-Row Circular Multi-Pass Cell

A new design of circular multi-pass cells (CMPC) with two rows of reflection spots on mirrors is presented. The effective optical path length (OPL) of this novel CMPC is double that of traditional CMPC with the same diameter and interval of spots. This OPL can be readily adjusted to have regular intervals by rough rotation adjustment. We achieved a spatial separation of pre- and post-transfer optical systems that was adequately large even in the cases with a large number of passes. Analytical chief ray tracing analysis and a generalized method for parameter determination for designing the cell are presented in detail. The stable condition of the double-row CMPC (DR-CMPC) is also derived by the ABCD matrix method. Designs with maximum effective OPL of 74.72 m, 48.67 m and 24.57 m are demonstrated and verified by ray tracing simulations within a 25 cm diameter DR-CMPC. An adjustment of the regular intervals to 1 m can be achieved in both designs. The overall astigmatism of the design with an effective OPL of 74.72 m is only 9.30 × 10⁻⁶ mm, which is four orders of magnitude smaller than that of the traditional CMPC with similar geometric parameters.

Compact optical multipass matrix system design based on slicer mirrors

High path-to-volume ratio (PVR) and low-aberration-output beams are the two main criteria to assess the performance of multipass absorption cells. However, no substantial progress has been reported for large-numerical-aperture-coupled multipass cells, which is due to the accumulated aberrations caused by a large number of off-axis reflections. Based on Chernin's design, in this study, we modified Chernin's four-objective multipass matrix cell by using slicer mirrors to eliminate alignment difficulty and decrease the system volume. A generalized design routine based on user requirements is also proposed. Based on the automatic modeling tool package (Pyzdde) connected with Zemax and boundary conditions of the parameters selection proposed, a low-aberration-output beam and a high PVR are easily obtained compared with other multipass cells schemes. In one demo design, 108 passes (5×7 matrix spots) in a base length of 300 mm are presented. The PVR and peak-to-valley value wavefront errors are 67.5 m/L and 0.92 μm, respectively. Finally, a tolerance analysis of this optical multipass system is also presented. This work may provide better broadband optical absorption cells in terms of response time and a better detection sensitivity in versatile applications.