Adjustable Optical Path Length Compact Spherical Mirrors Multipass Cell Optimized with Genetic Algorithm

Summary form only given. Numerous practical applications, including health and environmental protection, need compact and high sensitivity gas sensors. This work reports an experimental investigation on a compact multipass cell (MPC) designed and optimized with a genetic algorithm (GA) with long, adjustable optical path length (OPL) using only inexpensive spherical mirrors. A four-mirror based MPC with the GA developed here, offers great design flexibility in comparison to a two-mirror solution. As an example, a stable 24 m OPL was reached within only 80 cc volume. Moreover, by changing the mirror positions various stable OPLs can be achieved in a controlable way. The presented MPC consists of four mirrors in a configuration similar to a bow-tie. As a result, the symmetry between the mirrors is broken (mirrors are not paraller to each other) and an astigmatic spot pattern with a high fill factor is obtained. Additionaly, the use of the folded optical path geometry causes higher compactness in contrast to an astigmatic mirror-based MPC. Compared to other dense-pattern or folded sperical mirrors MPCs reported previously [1-3], longer OPL in the same volume can be obtained. In order to accurately calculate the line-sphere intersection points and reflection angles based on algorithms reported in [4] custom ray tracing software was developed. It also allows to determine the optimal MPC configuration with specified design constraints (mirror diameters, their focal lengths and desirable OPL) by using a GA [5].