Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy
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- Baer, D., Paul, J., Gupta, M. et al. Appl Phys B (2002) 75: 261. doi:10.1007/s00340-002-0971-z
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A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1×10-11 cm-1 Hz-1/2. The instrument has been used for sensitive measurements of CO, CH4, C2H2 and NH3.