Broadband calibration-free cavity-enhanced complex refractive index spectroscopy using a frequency comb

We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement...

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Bibliographic Details
Published in:arXiv.org 2018-05
Main Authors: Johansson, Alexandra C, Rutkowski, Lucile, Filipsson, Anna, Hausmaninger, Thomas, Zhao, Gang, Axner, Ove, Foltynowicz, Aleksandra
Format: Article
Language:English
Subjects:
Broadband
Calibration
Dispersion
Fabry-Perot interferometers
Fourier transform spectrometers
Fourier transforms
Molecular absorption
Optical frequency
Refractivity
Spectroscopy
Spectrum analysis
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Summary:We present broadband cavity-enhanced complex refractive index spectroscopy (CE-CRIS), a technique for calibration-free determination of the complex refractive index of entire molecular bands via direct measurement of transmission modes of a Fabry-Perot cavity filled with the sample. The measurement of the cavity transmission spectrum is done using an optical frequency comb and a mechanical Fourier transform spectrometer with sub-nominal resolution. Molecular absorption and dispersion spectra (corresponding to the imaginary and real parts of the refractive index) are obtained from the cavity mode broadening and shift retrieved from fits of Lorentzian profiles to the individual cavity modes. This method is calibration-free because the mode broadening and shift are independent of the cavity parameters such as the length and mirror reflectivity. In this first demonstration of broadband CE-CRIS we measure simultaneously the absorption and dispersion spectra of three combination bands of CO2 in the range between 1525 nm and 1620 nm and achieve good agreement with theoretical models. This opens up for precision spectroscopy of the complex refractive index of several molecular bands simultaneously.
ISSN:2331-8422
DOI:10.48550/arxiv.1805.00799