Simultaneous On-Line Measurement of Exhaled Carbon Dioxide and Water Vapor Based on 2.73 mu m Distributed Feedback Laser

The concentration changes of exhaled carbon dioxide and water vapor arc closely related to the physical condition. Therefore, it is of great significance to detect their concentrations. An exhaled gas detection device based on a 2.73 mu m distributed feedback laser is proposed. Spectral lines at 3659.102 cm(-1) and 3659.931 cm(-1) arc selected to measure carbon dioxide and water vapor respectively by using the wavelength modulation spectroscopy. The results show that using the second harmonic signal to calibrate the gas concentration, the linearity of 0.99915 and 0.99679 is obtained when the volume fractions of carbon dioxide and water vapor arc less than 35% and 2.3%, respectively. The concentrations of carbon dioxide and water vapor during the respiratory cycle arc measured in real time. With the measurement time of 0.92 s, the sensor achieves a detection sensitivity of 1.33X 10(-3) and 1.37X 10(-4) for carbon dioxide and water vapor, respectively. At the acquisition time of 56.8 s, the detection accuracy with 0.12% of carbon dioxide is achieved, and a detection limit of 1. 19 X 10(-4) at the optimal integration time of 17 min is achieved for carbon dioxide measurement.