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(a) The PA signals changing with CO2 concentration range from 0 ppm to 80 ppm using the QCL; (b) The PA signals changing with CO2 concentration range from 0 % to 100 % using DFB (Localized enlargement of the 50ppm-20 % concentration range is shown in the small figure); (c) The resonance frequency changing with CO2 concentration from 0 % to 100 % using He-Ne Laser.
