Cavity enhanced absorption spectroscopy of molecular carbon dioxide near IR region with a DFB diode laser

This paper is about cavity enhanced absorption spectroscopy (CEAS) experiment with a tunable narrow line width continuous wave DFB diode laser; and it was used to measure the weak absorption band of carbon dioxide in the near infrared region. The absorption spectrum was extracted from the measurement of light intensity that leaks out of an optical cavity which was consisted of two high reflectivity mirrors separated at a distance about 34cm. In the experiment, the optical cavity was scanned continuously and the laser radiation was coupled into the optical cavity via accidental coincidences of laser frequency with one of the multitude modes of the optical cavity. A wavemeter was used simultaneously to record the accurate wavelength of the DFB diode laser radiation. Absorption spectrum of vibrational combination band of carbon dioxide near 6358.65cm-1 has been obtained. An absorption sensivity of about 3.6 x 10(-7) cm(-1) has been achieved. The experimental results indicate that cavity enhanced absorption spectroscopy can be used as a high sensitive direct absorption spectroscopy technology.