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Author(s):Foltynowicz, Aleksandra
Abstract:Fourier transform spectroscopy (FTS) based on optical frequency combs offers a number of advantages over conventional Fourier transform infrared (FTIR) spectroscopy based on incoherent sources\footnote{J. Mandon, G. Guelachvili, and N. Picque, Nat. Photonics 3, 99 (2009).}. The high spectral brightness of the comb sources allows measuring spectra with high signal-to-noise ratios in acquisition times of the order of seconds. What is more, the resolution of comb-based FTS is given by the linewidth of the comb modes rather than the optical path difference (OPD) in the spectrometer, provided that the OPD is matched to the inverse of the comb mode spacing\footnote{P. Maslowski, et al., Phys. Rev. A 93, 021802 (2016); L. Rutkowski, et al., J. Quant. Spectrosc. Radiat. Transf. 204, 63 (2018).}. This implies that spectra with kHz resolution can be measured using OPD of the order of a few tens of cm\footnote{L. Rutkowski, et al., Opt. Express 25, 21711 (2017).}, which is impossible in conventional FTIR spectrometers. To increase the sensitivity of direct absorption measurements, frequency combs can be efficiently coupled into enhancement cavities that increase the interaction length with the sample\footnote{M. J. Thorpe, and J. Ye, Appl. Phys. B 91, 397 (2008); A. Foltynowicz, et al., Phys. Rev. Lett. 107, 233002 (2011).}. In another cavity-enhanced approach, the profiles of the cavity modes are measured directly, and complex refractive index spectra of entire molecular bands are determined from the broadening and shift of the cavity modes caused by the molecular sample\footnote{A. C. Johansson, et al., Opt. Express 26, 20633 (2018).}. Comb-based FTS can also be combined with other detection methods, such as Faraday rotation spectroscopy to detect broadband interference-free spectra of paramagnetic molecules\footnote{A. C. Johansson, J. Westberg, G. Wysocki, and A. Foltynowicz, Appl. Phys. B 124, 79 (2018).}, or photoacoustic spectroscopy that allows detection in a very small sample volume\footnote{I. Sadiek, et al., Phys. Chem. Chem. Phys. 20, 27849 (2018).}. I will present the various implementations of comb-based FTS and show examples of high-resolution measurements of entire absorption bands in the near- and mid-infrared wavelength range.
Issue Date:2019-06-20
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Rights Information:Copyright 2019 Aleksandra Foltynowicz
Date Available in IDEALS:2019-07-15

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