Parabolic multi-pass cell with high detection sensitivity and compact structure

A multi-pass cell is an important component in tunable diode laser absorption spectroscopy. In this paper, a type of multi-pass cell with two parabolic mirrors is proposed, and the analytical expressions of the rays transmitted between the mirrors are derived based on the vector reflection theory. Since no paraxial approximation is brought into the calculating process, the ray can be traced accurately. Subsequently, the design process of the parabolic multi-pass cell is depicted in detail, and simulations are conducted to validate the design process. TracePro is also utilized to demonstrate the validity of the calculating method. Moreover, the method for scaling up or down the spot pattern is introduced, enabling flexible adjustment of the optical path length and volume of the MPC; thus, the optical path length and volume of the multi-pass cell can be adjusted as needed. Finally, simulations are performed with the method proposed to search for parabolic multi-pass cells with high performance. The results show that these parabolic MPCs can achieve an optical path length of up to 128.7 m while maintaining a compact volume of no more than 100 mL. Consequently, the parabolic multi-pass cell possesses high detection sensitivity and a compact structure. The design method is of significance for the design of multi-pass cell and its application in gas sensing technologies.