We demonstrate that the large FM noise of a semiconductor laser can be combined with a squeezed AM noise spectrum to make a sub-shot-noise, FM-noise-based spectroscopic measurement. In particular, we probe the spectrum of magneto-optically trapped and cooled rubidium atoms using the FM noise on squeezed AM background noise. The natural absorption line as well as a stimulated Raman transition are clearly visible in the FM-to-AM converted noise even though the signal is below the classical shot-noise level.
© 1998 Optical Society of America
(000.1600) General : Classical and quantum physics
(140.5960) Lasers and laser optics : Semiconductor lasers
(270.5290) Quantum optics : Photon statistics
(270.6570) Quantum optics : Squeezed states
Steven Kasapi, Seema Lathi, and Yoshihisa Yamamoto, "Sub-shot-noise FM noise spectroscopy of trapped rubidium atoms," J. Opt. Soc. Am. B 15, 2626-2630 (1998)