Frequency-modulation (FM) spectroscopy is known to be a sensitive spectroscopic technique capable of accurately measuring the frequency dependence of the absorption and index of refraction of narrow spectral features. The absorption and index of refraction are coupled by a form of the Kramers–Kronig (K-K) relations, and both components provide information about the spectral feature. In this Letter, we propose a processing technique based on fitting the data to a complex signal model derived from the K-K relation. By using this complex constraint and only processing a single quadrature, our model predicts significant improvement in the minimum detectable absorption compared with conventional FM spectroscopy.
© 2011 Optical Society of America
Original Manuscript: October 14, 2010
Manuscript Accepted: December 20, 2010
Published: January 25, 2011
Vahid Ataie and George Papen, "Improved sensitivity of intensity-modulated spectroscopy using correlative signal processing," Opt. Lett. 36, 346-348 (2011)