Precise 13CO2/12CO2 isotopic ratio measurements for breath diagnosis with a 2 μm diode laser

A laser spectrometer based on a distributed-feedback semiconductor diode laser at 2 mu m is developed to measure the changes of (CO2)-C-13/(CO2)-C-12 isotope ratio in exhaled breath sample with the CO2 concentration of similar to 4%. It is characterized by a simplified optical layout, in which a single detector and associated electronics are used to probe CO2 spectrum. The cell has 10 cm long base length with 26.4 m optical path length in total and 330 cm(3) volume. The cell pressure and temperature are controlled at 50 Torr and 28 degrees C, respectively. The best (13)delta precision of 0.06 parts per thousand was achieved by using wavelet denoising and Kalman filter.