Physical Review A

Statistical-noise properties of an optical amplifier utilizing two-beam coupling in atomic-potassium vapor

William V. Davis, Alexander L. Gaeta, Robert W. Boyd, G. S. Agarwal

Published May 1, 1996• 5 citations

Abstract

We have measured the gain and statistical-noise properties of a weak probe beam amplified through two-beam coupling in atomic-potassium vapor for both the Rabi and stimulated Rayleigh gain features. The probe-beam gain was observed to be as large as 125 for the Rabi feature, whereas the gain was typically less than 2 for the Rayleigh feature. The rms noise at the Rabi gain feature was approximately three times greater than the ideal amplifier quantum-noise limit. For the Rayleigh gain feature, the rms noise was 12 to 15 times greater than the ideal amplifier quantum-noise limit. We present a fully quantum-mechanical theory of two-beam coupling in a system of two-level atoms which includes the effects of atomic motion and pump-beam absorption. The predictions of this theory are in good agreement with the experimental data. \textcopyright{} 1996 The American Physical Society.

DOI: 10.1103/physreva.53.3625

Related papers

Quantum-noise limit on optical amplification by two-beam coupling in an atomic vapor

Alexander L. Gaeta, Robert W. Boyd, G. S. Agarwal

We investigate theoretically the noise properties of the amplification of a weak probe beam in an atomic vapor pumped by an intense nearly resonant pump field. For the case of gain via the three-photon effect, we find that only in the limit in which collisional broadening is absent can the system operate as an ideal quantum-noise limited optical amplifier for the probe wave. For the case of gain via stimulated Rayleight scattering, we find that the minimum noise figure is four times that of an ideal optical amplifier, and that it occurs when the atomic system is predominantly collisionally broadened.

Physical Review AOct 1, 199218 citations

Noise properties of probe-beam amplification through two-beam coupling in potassium vapor

William V. Davis, Alexander L. Gaeta, Martti Olavi Kauranen +1 more

There is great interest in developing low-noise optical amplifiers that can be used in optical communication systems. Optical amplifiers have been constructed from laser amplifiers, optical fibers, Raman cells, χ(2) nonlinear crystals, and atomic vapors. Optical amplifiers that make use of two- beam coupling in atomic vapors are particularly important since they are able to amplify a continuous-wave multiple-transverse-mode optical signal with a single-pass gain greater than 10 at the bandwidths necessary for optical communications.1 For these reasons, we present an experimental and theoretical study of the noise properties of a probe beam amplified through two-beam coupling in potassium vapor. We also describe the conditions under which this optical amplifier can operate as a quantum-noise-limited linear amplifier.

Quantum Electronics and Laser Science ConferenceMay 2, 19930 citations

Laser Beam Combining Through The Nonlinear Response Of A Strongly Driven Atomic Transition

Kenneth R. MacDonald, Mark T. Gruneisen, Robert W. Boyd

We present the results of an experimental and theoretical study of the gain experienced by a weak probe beam propagating through a sodium vapor in the presence of an intense pump field that is nearly resonant with the 3s→3p atomic transition. This interaction provides a means by which the outputs of two lasers can be combined coherently. The probe transmission spectrum is comprised of three distinct features, two of which result in amplification of the probe wave. The origin of these features can be traced to the modification of the atomic level structure by the ac Stark effect. The experimentally measured spectra are in good agreement with the predictions of a theoretical model based on the solution of the density-matrix equations of motion for a two-level atom and including the effects of Doppler broadening. The dependence of the induced gain on the pressure of a helium buffer gas has been measured and is in good agreement with the predictions of theory. The maximum gain observed in these experiments occurs at one of the Rabi sidebands and leads to a 38-fold increase in the intensity of the probe wave.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEApr 8, 19880 citations

Amplification of vacuum fluctuations by two-beam coupling in atomic vapors

Martti Olavi Kauranen, Alexander L. Gaeta, Robert W. Boyd +1 more

We show both theoretically and experimentally that fluctuations of a weak probe beam are increased above the coherent-state shot-noise level as the beam interacts with a strong degenerate pump beam in an atomic vapor. The origin of this noise amplification process is the two-beam-coupling process between the pump beam and the vacuum sidebands of the probe beam. The major contribution to this excess noise arises from the quantum fluctuations of the atomic medium that are induced by the pump beam. We believe that this mechanism can be important in preventing the reduction of noise below the quantum-noise limit in experiments that utilize atomic vapors.

Physical Review AAug 1, 199421 citations

Observation of large continuous-wave two-photon optical amplification

Hope M. Concannon, William J. Brown, Jeff R. Gardner +1 more

We observe 30% two-photon optical amplification of a probe laser-field propagating through a laser-pumped potassium vapor. This amplification is spectrally isolated and substantially larger than that of previously reported continuous-wave two-photon amplifiers. The combination of large amplification and spectral isolation of the two-photon gain feature will greatly facilitate precise studies of the photon statistics of this highly nonlinear quantum amplifier and the development and characterization of a two-photon laser based on this gain medium. We also observe spectrally-distinct three-photon amplification $(\ensuremath{\sim}5$%) in the same system under different experimental conditions. We present a simple model of the interaction that gives qualitative agreement with our observations and explains the dependence of the two-photon gain on the various system parameters. This model predicts that the size of the two-photon gain is quite sensitive to an interference between two different quantum pathways.

Physical Review AAug 1, 199725 citations

Nonlinear optical experiments in sodium vapor and comparison with Doppler-broadened two-level-atom theory.

John F. Valley

Two spectral regions of gain exist for a weak probe beam propagating through a medium of two-level-atoms pumped by a strong near-resonance field. Experimentally a cw ring-dye laser is used to explore this gain at the Na D₂ resonance in a vapor. Plane-wave calculations of probe-gain spectra which include the Doppler broadening inherent in a vapor agree well with experimental spectra obtained with a Fabry-Perot interferometer. Such two-beam-coupling gain might have applications as optical pre- or power amplifiers. The gain is also the primary step in four-wave-mixing. Mixing of the pump and sideband which experiences gain produces the medium polarization from which the fourth-wave arises. For phase-matched propagation the fourth-wave, which is at a frequency that experiences little or negative probe-gain (i.e., absorption), grows at nearly the same rate as the primary sideband. Together the two sidebands extract far more than twice as much energy from the pump than does the primary sideband acting alone. Experimentally four-wave-mixing which arises from noise at the gain-sideband-frequency is sometimes accompanied by conical emission at the fourth-wave sideband. Since this sideband is also seen on axis the explanation cannot be simply phase-matching. Simulations which include the full transverse nature of the experiment are currently running on a CRAY supercomputer. These simulations indicate that the radial variation of the medium index of refraction is responsible for conical emission.

Jan 1, 19890 citations