Optical multipass cell based on two cylindrical mirrors for high sensitivity detection of methane

Abstract

The optical multipass cell has been widely used in the detection of absorption spectroscopy to increase the optical path length and improve the detection sensitivity. A multipass optical cell based on two cylindrical mirrors is described for application to tunable diode laser absorption spectroscopy. The multipass cell has the characteristics of simple and compact structure, high efficient use of mirror area, longer optical path length at the same base length compared with traditional multipass cells. Rotation of the cylindrical mirrors and variation in the cell base length have been used to achieve different spot patterns and path lengths. CH4 direct absorption measurement using the multipass cell with a fibre-coupled distributed-feedback laser at 1.653 μm has been performed. Detection sensitivity of 0.68 μmol/mol is realized for absorption optical path length of 13.8 m, and the detection of atmospheric CH4 has been achieved with the system.