Abstract

Squeezed states of light exhibit phase-sensitive quantum noise measurable via optical homodyne detection. They have been predicted to be generated via degenerate four-wave mixing, resonance fluorescence, and nonlinear propagation.¹ We report observing phase-sensitive noise via optical homodyning on a cw dye laser beam which has propagated through sodium vapor near the D lines. A p-polarized dye laser beam of ~5-W/cm² intensity was passed through sodium vapor near its D lines. Homodyne measurements were made on both the s- and the p-polarized components of the transmitted beam using the dual-detector subtraction scheme.² A spectrum analyzer monitored the noise in a 6–15-MHz band. In the absence of sodium, the noise in this band was vacuum-state quantum noise limited and was insensitive to the relative local-oscillator beam/transmitted laser beam phase θ. In the presence of sodium, the noise was sensitive to θ, with dependence of the form A_s,p + B_s,p cos²(θ − ϕ_s,p), where ϕ_s = 0 for s polarization and ϕ_p = π/2 for p polarization. For one set of data we measured A_s = 2 dB, B_s = 3 dB, A_p = 3 dB, and B_p = 2.5 dB above the noise levels in the absence of sodium. The s-poiarization data were collected with the local-oscillator power P_LO far in excess of the s component of the transmitted pump power P_TP; for p polarization, P_LO ~ P_TP prevailed. The measurement uncertainty in the spectrum analyzer data is ±0.5 dB. Possible physical mechanisms to explain these results are discussed.

© 1985 Optical Society of America