Denis V. Brazhnikov

Electromagnetically-induced-absorption resonance with high contrast and narrow width in the Hanle configuration

The method for observing the high-contrast and narrow-width resonances of electromagnetically induced absorption (EIA) in the Hanle configuration under counterpropagating light waves is proposed. We theoretically analyze the absorption of a probe light wave in presence of counterpropagating one with the same frequency as the function of a static magnetic field applied along the vectors of light waves, propagating in a vapour cell. Here, as an example, we study a “dark” type of atomic dipole transition Fg=1→Fe=1 in D1 line of Rb, where usually the electromagnetically induced transparency (EIT) can be observed. To obtain the EIA signal one should proper chose the polarizations of light waves and intensities. In contrast of regular schemes for observing EIA signals (in a single travelling light wave in the Hanle configuration or in a bichromatic light field consisted of two traveling waves), the proposed scheme allows one to use buffer gas to significantly enhance properties of the resonance. Also the dramatic influence of atomic transition openness on contrast of the resonance is revealed, that gives great advantage in comparison with cyclic atomic transitions. The obtained results can be interesting in high-resolution spectroscopy, nonlinear and magneto-optics. PACS: 42.50.Gy; 32.70.JzThe method for observing the high-contrast and narrow-width resonances of electromagnetically induced absorption (EIA) in the Hanle configuration under counter-propagating pump and probe light waves is proposed. Here, as an example, we study a ?dark? type of atomic dipole transition in D1 line of 87Rb, where usually the electromagnetically induced transparency can be observed. To obtain the EIA signal one should properly choose the polarizations of light waves and intensities. In contrast to regular schemes for observing EIA signals (under a single traveling light wave in the Hanle configuration or under a bichromatic light field consisting of two traveling waves), the proposed scheme allows one to use buffer gas for significantly improving the properties of the resonance. Also the dramatic influence of atomic transition openness on the contrast of the resonance is revealed, which is advantageous in comparison with cyclic atomic transitions. The nonlinear resonances in a probe-wave transmitted signal with contrast close to 100% and sub-kHz widths can be obtained. The results are interesting in high-resolution spectroscopy, nonlinear and magneto-optics.

Nonlinear propagation of polarized light pulses in a medium of atoms with degenerate energy levels: Adiabatic approach

We develop a general method allowing one to construct the consistent theory of light pulse propagation through an atomic medium in arbitrary nonlinear regime with respect to the field strength, taking into account the light polarization, temporal (frequency), and spatial dispersions. The method is based on the reduced Maxwell equation, atomic density matrix formalism, and adiabatic approximation. In order to demonstrate the efficiency of our method we investigate in detail the case of propagation of the pulses under conditions of coherent population trapping in a medium of two-level atoms with degenerate energy levels. Equations describing the evolution of various field parameters are derived. It is shown that pulses of ellipticity and spatial orientation of polarization ellipse propagate with slowing. Analytical expressions for the slowing factor are obtained. Previously unknown effects of the stimulated phase modulation and the generation of a phase pilot pulse by the variation of spatial orientation of the polarization ellipse are predicted.

Propagation of the phase pulses of bichromatic radiation under the electromagnetically induced transparency conditions

We study the dynamics of the phase pulses of laser radiation with two resonant frequency components propagating in an atomic three-level Λ type medium under coherent population trapping. Using the density matrix adiabatic approach we show that the effect of a very large slowing down occurs not only for amplitude pulses, but also for phase pulses. The group velocity of phase pulses can be controlled by the amplitudes of resonant fields. The analytical solution describing the mutual influence of the phase modulation of one field component on another is obtained.

Ultrahigh-contrast saturated-absorption resonance to enhance stability of CPT atom clocks

The results of detailed experimental and theoretical investigations of new nonlinear effect in the field of saturated-absorption spectroscopy of atom vapours are presented. The effect consists in observation of a high-contrast natural-linewidth absorption spike when 133Cs atoms are being irradiated by the bichromatic counterpropagating laser beams. The results obtained can be useful in various fields of modern laser physics and applications where saturated-absorption resonances are used. For instance, the effect has been already implemented in the coherent-population-trapping atom clocks to enhance stabilization of optical frequencies and to improve stability of the clocks on the whole.

Analytical expressions for parameters of the dark resonance in a vacuum vapour cell

In spite of great number of papers devoted to theoretical and experimental study of the coherent population trapping phenomenon (CPT), still there is a lack of analytical results for the properties of the CPT-caused dark resonance in some principal cases. We will present the results of our study for single and double A schemes of atomic energy levels, which are of great importance for various applications of CPT (atom clocks, magnetometers, etc.). Analytical expressions for width and amplitude of the dark resonances have been obtained, which are valid for wide range of light wave intensities. The results concern closed as well as open A schemes. We will also discuss the difference between the two A schemes and state the condition when a double scheme can be effectively treated as a single A scheme. The analytical approximate formulas obtained have been compared with exact numerical solutions based on the optical Bloch equations as well as experimental.

An optical frequency standard based on ultracold magnesium atoms

This paper presents the recent experimental results on development of an optical frequency standard based on ultra cold magnesium atoms with relative frequency uncertainty and long term stability at the level of / <10 . We stabilized the frequency of our clock laser system at 655 THz to narrow Ramsey fringes in a time separated laser fields interacting with cooled Mg atoms localized in a magneto-optical trap (MOT). The intercombination line S0→P1 was used as the reference for frequency stabilization. The results of stabilization were studied with femtosecond comb based on Ti:Sa laser. Optical frequency standards based on cooled and localized atoms play an important role in both fundamental research and various metrological and navigational applications. Alkaline-earth and alkaline-earth-like atoms such as Yb [1], Ca [2], Sr [3–5], Hg [6] and Mg [7, 8] are the main candidates to create frequency standards of a new generation. Today, Yb and Sr optical-lattices frequency standards demonstrate a relative instability and uncertainty of extremely low levels 10÷10 [1, 4]. Mg frequency standard at the moment much less developed compare to Sr and Yb optical standards. At the same time, magnesium atoms have some advantages compared to the other candidates in terms of the frequency standard. Thus, the blackbody radiation (BBR) shift of the clock transition for magnesium is much smaller than for Yb, Ca, Sr. The simplified level scheme of Mg atoms is shown at figure 1. Figure 1. Simplified term diagram of Mg atoms. Solid lines denote the cooling transitions with corresponding temperature limits, while dashed lines denote possible “clock” transitions, which can be used for laser frequency stabilization. MPLP-2016 IOP Publishing IOP Conf. Series: Journal of Physics: Conf. Series 793 (2017) 012008 doi:10.1088/1742-6596/793/1/012008 International Conference on Recent Trends in Physics 2016 (ICRTP2016) IOP Publishing Journal of Physics: Conference Series 755 (2016) 011001 doi:10.1088/1742-6596/755/1/011001 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 The resonant strong transition S0→P1 is a very suitable for an effective laser cooling and trapping of Mg atoms in a magneto-optical trap (MOT) directly from a thermal atomic beam. The Mg S0→P1 transition natural width is only 31 Hz and it could be used to develop an optical frequency standard with high long term frequency stability. Strongly forbidden S0→P0 transition is of particular interest to develop an “optical lattice” standard with relative frequency uncertainty of 10÷10. To observe S0→P0 transition the magnetic-field-induced spectroscopy method could be used [9]. Despite a number of difficulties for deep cooling of Mg atoms down to a temperature less than 100 μK due to a large value of recoil energy, studies aimed at creating an optical frequency standard based on Mg atoms are carried out at the Institut für Quantenoptik, Hannover, Germany [7] and the Institute of Laser Physics, Novosibirsk, Russia [8] In our previous studies we localized a cloud of cooled Mg atoms in MOT and have observed narrow Ramsey resonances in time separated laser fields at the intercombination transition S0→P1 [8]. This paper presents preliminary results on a clock laser frequency stabilization using Ramsey resonances and a frequency stability measurements with a frequency comb generator based on a femtosecond Ti:Sa laser. A schematic diagram of Mg optical frequency standard is shown at figure 2. Figure 2. Simplified schematic of the experimental setup, showing the 914 nm Ti:Sa laser, the cavity with KNbO3 crystal for frequency doubling to the “clock” wavelength of 457 nm, the reference cavity for Ti:Sa laser linewidth preliminary narrowing, the zerodur cavity with a two pass acousto-optical modulator (AOM) for frequency stabilization and fine tuning of the clock laser frequency, the MOT with a detection system. The frequency of clock laser system was stabilized using a highly stable zerodur cavity and was tuned with the generator Agilent N5181A controlled AOM. A digital version of the third harmonic detection method is used to generate an error signal for frequency stabilization of the clock laser system to a central Ramsey fringe [10]. The four radio frequencies were generated with four channel DDS generator. These frequency were ∆1 = f0+∆/4, ∆-1 =f0–∆/4, ∆3 = f0+3∆/4, ∆-3 =f0–3∆/4, were ∆ is a value of the Ramsey fringes period, f0 = 80 MHz is a central frequency of AOM, that formed time separated pulses for cooled Mg atoms excitation. A calculated error signal dS=(S∆-3–3S∆-1+3S∆1–S∆3) MPLP-2016 IOP Publishing IOP Conf. Series: Journal of Physics: Conf. Series 793 (2017) 012008 doi:10.1088/1742-6596/793/1/012008

New approaches in deep laser cooling of magnesium atoms for quantum metrology

We theoretically describe two approaches aimed at solving the existing problem of deep laser cooling of neutral magnesium atoms. The first approach based on using optical molasses with orthogonal linear polarizations of light waves, while the second one implies exploiting “nonstandard” magneto-optical trap composed of elliptically polarized (in general) light waves. The widely used semiclassical approximation based on the Fokker-Planck equation as well as the full quantum treatment (with full account of the recoil effect) are applied for theoretical analysis. The results are crucial for metrological and some other applications of cold atoms.

Effective polarization method for controlling a sign of the nonlinear subnatural resonances

We propose the effective and easy method for controlling a sign of narrow resonances of electromagnetically-induced transparency (EIT, [1,2]) and absorption (EIA, [3]). These nonlinear resonances are the bright examples of the nonlinear effects based on the low-frequency atomic coherences. The former effect is connected with the phenomenon of the coherent population trapping (CPT, [4]), while the latter is described by the spontaneous coherence transfer from excited state to ground one [5]. Widths of the EIA and EIT signals can be much less than the natural width. Therefore, they are often called subnatural resonances. EIT and EIA have already found numerous applications in nonlinear optics (e.g., four-wave mixing), optical communications (so-called “slow” and “fast” light), metrology (miniature atomic clocks and magnetometers), laser physics and so on.

New Doppler-free resonance in counterpropagating light waves

The resonance of saturated absorption in counterpropagating light fields is experimentally and theoretically studied. We focus on a case of parallel and linearly polarized waves, driving an open dipole transition in rubidium vapor. A new Doppler-free resonance within the saturated-absorption dip is revealed. The phenomenon can be gained only in absorption of strong wave in presence of weak one. The effect can not be explained basing on the previously known reasons. The results obtained can be found useful in metrology for the frequency and time standards.

New features of Doppler-free saturated-absorption resonance in field of counterpropagating waves

The resonance of saturated absorption in counterpropagating light fields is experimentally and theoretically studied. We focus on two cases: parallel and linearly polarized waves, driving an open dipole transition and the general case of elliptically polarized waves, driving closed dipole transition. The former reveals a new Doppler-free resonance as a peak within the saturated-absorption dip. The latter case reveals a new polarization effect, causing a shift and asymmetry of the saturated-absorption resonance. The results obtained can be found useful in metrology.