Absorption spectroscopy with femtosecond frequency comb lasers for breath analysis

Document Type : Original Article

Authors

1 Laser Institute for Research and Applications )LIRA(, Beni-Suef University, Beni-Suef 62511, Egypt.

2 Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA

Abstract

An optical setup based on a frequency comb laser and a multipass optical cell has been developed for breath analysis. The frequency comb laser is a broadband Er+ fiber laser beam in a range spanning from 1500 nm to 1700 nm.  The multipass optical cell is formed by six highly reflective confocal mirrors to achieve a long optical path of 300 m in a cell of only 0.5 m in length. For testing the optical setup, the absorption laser spectroscopy measurements in the near IR of the gases CO2, CO, and CH4 were carried out. In the case of CH4 a signal to noise ration of 120 was obtained, yielding an estimated sensitivity of 6 ppmv. The dispersion of the femtosecond laser pulse in a multipass cell filled with methane gas at atmospheric pressure was studied. In the case of 1.64 µm and after 600 reflections, the femtosecond laser pulse was temporally broadened and the laser pulse duration changed from 108 fs to 326 fs. To compensate for this broadening, dispersive mirrors with suitable parameters are being proposed.

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