Vladimir A. Sautenkov

ULTRASLOW GROUP VELOCITY AND ENHANCED NONLINEAR OPTICAL EFFECTS IN A COHERENTLY DRIVEN HOT ATOMIC GAS

We report the observation of small group velocities of order 90 meters per second, and large group delays of greater than 0.26 ms, in an optically dense hot rubidium gas (≈ 360 K). Media of this kind yield strong nonlinear interactions between very weak optical fields, and very sharp spectral features. The result is in agreement with previous studies on nonlinear spectroscopy of dense coherent media.

Single-shot detection of bacterial endospores via coherent Raman spectroscopy

Recent advances in coherent Raman spectroscopy hold exciting promise for many potential applications. For example, a technique, mitigating the nonresonant four-wave-mixing noise while maximizing the Raman-resonant signal, has been developed and applied to the problem of real-time detection of bacterial endospores. After a brief review of the technique essentials, we show how extensions of our earlier experimental work [Pestov D, et al. (2007) Science 316:265–268] yield single-shot identification of a small sample of Bacillus subtilis endospores (≈104 spores). The results convey the utility of the technique and its potential for “on-the-fly” detection of biohazards, such as Bacillus anthracis. The application of optimized coherent anti-Stokes Raman scattering scheme to problems requiring chemical specificity and short signal acquisition times is demonstrated.

Electromagnetically induced transparency controlled by a microwave field

We have experimentally studied the propagation of two optical fields in a dense rubidium (Rb) gas in the case when an additional microwave field is coupled to the hyperfine levels of Rb atoms. The Rb energy levels form a close-

Nonlinear optics via double dark resonances

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Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas

three-level system coupled to the optical fields and the microwave field. It has been found that the maximum transmission of the probe field depends on the relative phase between the optical and the microwave fields. We have observed both constructive and destructive interferences in electromagnetically induced transparency. A simple theoretical model and a numerical simulation have been developed to explain the observed experimental results.

Coherent versus incoherent Raman scattering : molecular coherence excitation and measurement

Double dark resonances originate from a coherent perturbation of a system displaying electromagnetically induced transparency. We experimentally show and theoretically confirm that this leads to the possibility of extremely sharp resonances prevailing even in the presence of considerable Doppler broadening. A gas of {sup 87}Rb atoms is subjected to a strong drive laser and a weak probe laser and a radio frequency field, where the magnetic coupling between the Zeeman levels leads to nonlinear generation of a comb of sidebands.

Optical imaging beyond the diffraction limit via dark states

We experimentally study the group time delay for a light pulse propagating through hot {sup 87}Rb vapor in the presence of a strong coupling field in a {lambda} configuration. We demonstrate that the ultraslow pulse propagation is transformed into superluminal propagation as the one-photon detuning of the light increases due to the change in the transmission resonance line shape. Negative group velocity as low as -c/10{sup 6}=-80 m/s is recorded. We also find that the advance time in the regime of the superluminal propagation grows linearly with increasing laser field power.

Enhancement of field generation via maximal atomic coherence prepared by fast adiabatic passage in Rb vapor

We present a comparative analysis of spontaneous and coherent Raman scattering on pyridine. The instantaneous excitation of the molecular coherence is done by a pair of ultrashort preparation pulses. Then, a long narrowband probe pulse is scattered off the molecular vibrations. The described hybrid technique allows for the single-shot acquisition of a background-free coherent Raman spectrum within the excitation band and its straightforward comparison with the spontaneous Raman measurements, performed in the same setup. We report a 10(5)-fold increase in the efficiency of the Raman scattering process due to the broadband pump-Stokes preparation. The coherence magnitude (approximately 0.5x10(-3)) is inferred experimentally, without a priori knowledge about the molecular structure.

Coherence brightened laser source for atmospheric remote sensing

We study the possibility of creating spatial patterns having subwavelength size by using the so-called dark states formed by the interaction between atoms and optical fields. These optical fields have a specified spatial distribution. Our experiments in Rb vapor display spatial patterns that are smaller than the length determined by the diffraction limit of the optical system used in the experiment. This approach may have applications to interference lithography and might be used in coherent Raman spectroscopy to create patterns with subwavelength spatial resolution.

Switching between photon-photon correlations and Raman anticorrelations in a coherently prepared Rb vapor

We experimentally demonstrated the enhancement of coherent Raman scattering in Rb vapor by exciting atomic coherence with fractional STIRAP. The results support the possibility of increasing the CARS sensitivity