Abstract
We report on broadband absorption spectroscopy in the near IR using a multipass cell design based on highly reflecting mirrors in a confocal arrangement having the particular aim of achieving long optical paths. We demonstrate a path length of 314 m in a cell consisting of two sets of highly reflecting mirrors with identical focal length, spaced 0.5 m apart. The multipass cell covers this path length in a relatively small volume of 1.25 l with the light beam sampling the whole volume. In a first application, the absorption spectra of the greenhouse gases , , and CO were measured. In these measurements we used a femtosecond fiber laser with a broadband spectral range spanning the near IR from 1.5 to 1.7 μm. The absorption spectra show a high signal-to-noise ratio, from which we derive a sensitivity limit of 6 ppmv for methane observed in a mixture with air.
© 2013 Optical Society of America
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