High-resolution cavity enhanced absorption spectroscopy using an optical cavity with ultra-high reflectivity mirrors

High-resolution cavity enhanced absorption spectroscopy (CEAS) using a 1.5 μm cw narrow line width tunable diode laser (TDL) and an optical cavity which consists of two ultra-high reflectivity (R>99.999%) mirrors separated at a distance of 60 cm is described. Laser radiation is coupled into the optical cavity via accidental coincidences of laser frequency with one of the multitude modes of the cavity. Absorption spectrum of the vibrational combination band of CO2 has been obtained, the absorption signals were extracted from a measurement recording only the highest light intensity at a specified time period that leaks out of the cavity. A wavemeter was used simultaneously to record accurate frequency of the laser. An absorption sensitivity of about 4.8×10−9 cm−1 has been achieved.