Treating the weak-sideband fields quantum mechanically, we study the effects of quantum noise on amplitudemodulation and frequency-modulation spectroscopy of two-level media. Our analysis demonstrates that quantum noise affects not only the intensities of the modulation sidebands but also their relative phase, which leads in particular to a quantum limit for frequency-modulation spectroscopy.
© 1986 Optical Society of America
David A. Holm and Murray Sargent, "Quantum theory of multiwave mixing. VI. Effects of quantum noise on modulation spectroscopy," J. Opt. Soc. Am. B 3, 732-740 (1986)