Design and simulation of a multipass cell consisting of two plane mirrors and a biconvex lens

We report a multipass cell (MPC) that consists of two inexpensive silver (or gold)-coated plane mirrors and a biconvex lens instead of expensive concave spherical mirrors. The silver (or gold)-coated two plane mirrors are separated by a biconvex lens with an inner hole for the detection of the gas flow. The two mirrors (diameter of 50.8 mm) and the convex lens (diameter of 50.8 mm) are mounted on an optical board with a dimension of 75  mm  *  75  mm  *  30  mm and 75  mm  *  75  mm  *  21  mm, and the inner diameter of the two quartz glass tubes is 48 mm with a hole for the detection of the gas in flow and out flow. For example, the plane MPC, which is ∼236  cm3 with 130 times reflections, is much smaller than a traditional concave spherical mirror based on a Herriott or a White MPC, which is ∼700  cm3 with 80 times reflections, and offers an effective optical path-length of about 31.32 m. This low cost, compact MPC is very suitable for various applications, such as climate change, environmental monitoring, and agriculture.