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 ($5\times 7$ 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.

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.

During this study we constructed a generalized parametric modified four-objective multipass matrix system (MMS). We used an optical system comprising four asymmetrical spherical mirrors to improve the alignment process. The use of a paraxial equation for the design of the front transfer optics yielded the initial condition for modeling our MMS. We performed a ray tracing simulation to calculate the significant aberration of the system (astigmatism). Based on the calculated meridional and sagittal focus positions, the complementary focusing mirror was easily designed to provide an output beam free of astigmatism. We have presented an example of a 108-transit multipass system ($5\times 7$ matrix arrangement) with a relatively larger numerical aperture source (xenon light source). The whole system exhibits zero theoretical geometrical loss when simulated with Zemax software. The MMS construction strategy described in this study provides an anastigmatic output beam and the generalized approach to design a controllable matrix spot pattern on the field mirrors. Asymmetrical reflective mirrors aid in aligning the whole system with high efficiency. With the generalized design strategy in terms of optics configuration and asymmetrical fabrication method in this paper, other kinds of multipass matrix system coupled with different sources and detector systems also can be achieved.

A biconic White multipass cell (bi-WMPC), designed as a compact, zero-geometrical-loss, anastigmatic optical system, capably used with an extended divergent source, is proposed. First, a skew ray-tracing model is developed for a conventional White-type multipass cell (WMPC), based on which the astigmatism is calculated, together with its sensitivity coefficients in relation to all-important optical structural parameters in various configurations. Next, a generalized bi-WMPC is designed to suppress the astigmatism, which leads to much smaller reflection spots on the field mirror compared to the conventional design. The demonstration of an optimized bi-WMPC initialized from a commercial WMPC (52 pass with a 0.8 m base length) suggests a 53 fold reduction of the wavefront error value from $79.187\lambda$ to $1.493\lambda$, as well as the path-to-volume ratio (PVR) increase from 20.8 to 35.2 m/L. These improvements are critical for the design of a compact WMPC with a path length of tens to hundreds of meters. Presently developed skew ray-tracing models for a WMPC can also be applied to other freeform surfaces to further compensate the inherent aberrations induced by multiple off-axis reflections.

Four-terminal tandem devices require sophisticated light management techniques to reach their optimal efficiency. We show that periodic arrays of tall nanoparticles are well-suited for this purpose, and demonstrate their use in a Perovskite-on-Silicon tandem model.

The optical axis sensitivity for the unit‐magnification multipass system (UMS) is presented by using a general misaligned optical element transfer model. The generalized sensitivity factors SD1, SD2, ST1, and ST2 influenced by both the axial and angular misalignments of the objective mirrors in a UMS have been calculated for the first time. The Bernstein‐Herzberg White Cells are used as an example, and their alignment tolerance and stability properties are found when their configurations change. The analysis in this paper is helpful for the design of other kinds of multipass gas cells (MGC) with high robustness and avoiding the violent vibration of the optical axis when the misalignment of each mirror is controlled within the tolerance range. Among the five possible perturbations sources, the misaligned factors (δ_ix, δ_iy, θ_ix) have more effects on the output beam’s position and the perturbed sources from (δ_ix, θ_ix) and (δ_iy, θ_iy) have more impacts on the output beam’s slope referred to as x‐axis and y‐axis, respectively. Higher reflection times mean smaller tolerance range. The results benefit the multipass cell design and the precise alignment of the mirrors within the cell with the purpose of long‐term stability in measurements.