Theoretical review of modulation spectroscopy

In recent years there has been renewed interest in using modulation spectroscopy for a variety of scientific and engineering applications. Modulation spectroscopy is often implemented with diode lasers which have the advantages of small size, non-intrusiveness, speed, and ease of use. Several theoretical frameworks have been developed to describe modulation spectroscopy and its limiting cases: frequency modulation spectroscopy (FMS), and wavelength modulation spectroscopy (WMS). In this paper we examine these frameworks and describe a general approach to modulation spectroscopy which takes into account the properties of semiconductor lasers.