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Squeezing induced finite refractive index-zero absorption

Hanan Ali Batarfi

Published Jan 1, 1997• 0 citations
OpenAlex

Abstract

we demonstrate that spectra of a probe beam probing an ensemble of tow -level atoms damped by a broadband squeezed vacuum and driven by weak laser may exhibit a large refractive index by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by resonant effect is due to coherent population oscillations . the same theoretical model also exhibits a large refractive index with zero absorption at the rabi sidebands and near resonance . these results may be verified by present experiments

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Journal of the Optical Society of America B•May 1, 1996•20 citations
we demonstrate that spectra of a probe beam probing an ensemble of tow -level atoms damped by a broadband squeezed vacuum and driven by weak laser may exhibit a large refractive index by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by resonant effect is due to coherent population oscillations . the same theoretical model also exhibits a large refractive index with zero absorption at the rabi sidebands and near resonance . these results may be verified by present experiments
We demonstrate that the spectra of a probe beam probing an ensemble of two-level atoms damped by a broadband squeezed vacuum and driven by a weak laser may exhibit a large refractive index accompanied by zero absorption when the probe beam frequency is tuned to the laser frequency. This resonant effect is due to coherent population oscillations. The same theoretical model also exhibits a large refractive index with zero absorption at the Rabi sidebands and near resonance. These results may be verified by present experiments.
A comprehensive study is made of the absorption spectrum of a weak-probe beam irradiating a two-level atom damped by a broadband squeezed vacuum and driven by a strong laser field. We show that for a resonant driving field whose phase does not coincide with the principal directions of the squeezing ellipse, the absorption spectrum is asymmetric and exhibits absorption-emission profiles at the Rabi sidebands. We find that this feature arises from unequal populations of the dressed states of the system, which occur when all components of the Bloch vector are coupled to the driving field. A symmetric spectrum with dispersionlike profiles at the Rabi sidebands is revealed for an off-resonant driving field. Furthermore, the spectrum may exhibit an emission profile at the central frequency, signifying an amplification of the probe beam. We point out that the amplification at the central component is not attributed to population inversion in both the atomic bare states and in the dressed atomic states. We find that the amplification originates from the coherent population oscillations and is impossible in the absence of the squeezed vacuum. In addition, we examine how these features are affected by the detuning of the driving field and an imperfect squeezed vacuum.
The fluorescence spectrum of a strongly driven two-level atom located inside an optical cavity damped by a narrow-bandwidth squeezed vacuum is studied. We use a dressed atom model approach, first applied to squeezed vacuum problems by Yeoman and Barnett, to derive the master equation of the system and discuss the role of the cavity and the squeezed vacuum in the narrowing of the spectral lines and the population trapping effect. We find that in the presence of a single-mode cavity the effect of squeezing on the fluorescence spectrum is more evident in the linewidths of the Rabi sidebands rather than in the linewidth of the central component. Even in the absence of squeezing, the cavity can reduce the linewidth of the central component almost to zero, whereas the Rabi sidebands can be narrowed only to some finite value. In the presence of a two-mode cavity and a two-mode squeezed vacuum the signature of squeezing is evident in the linewidths of all spectral lines. We also establish that the narrowing of the spectral lines is very sensitive to the detuning of the driving field from the atomic resonance. Moreover, we find that the population trapping effect, predicted for the broadband squeezed vacuum case, may appear in a narrow-bandwidth case only if the input squeezed modes are perfectly matched to the cavity modes and if there is non-zero squeezing at the Rabi sidebands.
The resonance fluorescence of a two-level atom driven by a coherent laser field and damped by a finite bandwidth squeezed vacuum is analysed. We extend the Yeoman and Barnett technique to a non-zero detuning of the driving field from the atomic resonance and discuss the role of squeezing bandwidth and the detuning in the level shifts, widths and intensities of the spectral lines. The approach is valid for arbitrary values of the Rabi frequency and detuning but for the squeezing bandwidths larger than the natural line-width in order to satisfy the Markoff approximation. The narrowing of the spectral lines is interpreted in terms of the quadrature-noise spectrum. We find that, depending on the Rabi frequency, detuning and the squeezing phase, different factors contribute to the line narrowing. For a strong resonant driving field there is no squeezing in the emitted field and the fluorescence spectrum exactly reveals the noise spectrum. In this case the narrowing of the spectral lines arises from the noise reduction in the input squeezed vacuum. For a weak or detuned driving field the fluorescence exhibits a large squeezing and, as a consequence, the spectral lines have narrowed linewidths. Moreover, the fluorescence spectrum can be asymmetric about the central frequency despite the symmetrical distribution of the noise. The asymmetry arises from the absorption of photons by the squeezed vacuum which reduces the spontaneous emission. For an appropriate choice of the detuning some of the spectral lines can vanish despite that there is no population trapping. Again this process can be interpreted as arising from the absorption of photons by the squeezed vacuum. When the absorption is large it may compensate the spontaneous emission resulting in the vanishing of the fluorescence lines.
We study the absorption spectra of a weak probe beam that interacts with a driven two-level atom in the presence of a squeezed vacuum. In particular, we focus on the behavior of the central resonance of the probe absorption spectra in the region of intermediate driving intensities and in the large squeezed photon number limit. Squeezing-induced pimples, hole-burning, and dispersive profiles at line center are displayed. These unusual spectral features are highly sensitive to the squeezing phase and to the Rabi frequency of the driving field. We present analytical conditions for the occurrence of these effects and find that they all take place in the vicinity of the critical point dividing the different dynamical regimes, probe absorption and amplification, of the atomic radiation. We also investigate analytically and numerically the two-time correlation functions of the atomic polarization and find that the cross correlations of the two dipole quadratures contribute symmetric (absorptionlike) spectral features to the absorption spectra, whereas the self-correlations contribute asymmetric (dispersionlike) spectral profiles, which disappear for the particular phase values Φ = 0, π. The physical origin of the unusual spectral profiles at line center is also discussed in terms of the coherent population oscillations.