Design and optimization of an elliptical cell for laser absorption spectroscopy

Abstract

An annular cell with elliptical cross section and small physical size is introduced and simulated for increasing the absorption length in the spectroscopy. In this investigation by changing of the geometrical radius of the ellipse an absorption length of 15.50 m is obtained. By the optimization of the cell and including the sagittal and tangential radius of the ellipse that reflect the beam, it is shown that at the obtained absorption length, it is possible to reduce the divergence of the beam down to 54 µm. Then, signal-to-noise ratio (SNR) is calculated for R(16) CO2 absorption line by assuming that the cell is filled by the gas. The results of this calculation indicated that under optimum condition the SNR can be increased up to 310. Finally, the cell is optimized using Genetic algorithm by including all the effective parameters which affect the efficiency of the cell. We found that in the best case an absorption length of 8.24 m with a SNR of 107 can be achieved when the geometrical radius of the cell being fixed at 5.95 and 4.59 cm. © 2018, Isfahan University of Technology. All rights reserved.