ISSN 0021-3640, JETP Letters, 2012, Vol. 96, No. 5, pp. 303–307. © Pleiades Publishing, Inc., 2012. Original Russian Text © A. Sargsyan, R. Mirzoyan, D. Sarkisyan, 2012, published in Pis’ma v Zhurnal Eksperimental’noi i Teoreticheskoi Fiziki, 2012, Vol. 96, No. 5, pp. 333–337. 303 The effect of coherent population trapping (CPT) and the resulting process of electromagnetically induced transparency (EIT) are widely implemented in metrology, magnetometry, deceleration of light and optical information coding, the problems of quantum communications, etc. (see [1–3] for a review). In par- ticular, the development of next-generation atomic clocks [4, 5] is of great applied interest. Coherent pop- ulation trapping underlies modern magnetometers for precise measurements of weak magnetic fields, as well as some other applications reviewed in [2, 3, 6]. The behavior of the EIT resonance of Na atoms in mag- netic fields of up to hundreds of Gauss was described by Motomura and Mitsunaga [7]. The absence of works on EIT in higher fields (>500 G) is probably due to the relative complexity of producing strong homo- geneous magnetic fields, since the EIT resonances are formed in cells with a length of a few centimeters filled with atomic alkali vapors. An important advantage of using a thin atomic vapor column with L = 30 μm is the possibility of implementing strong permanent magnets that can produce B fields of up to thousands of Gauss over a distance of a few centimeters. The field of such permanent magnets is strongly inhomoge- neous. Its gradient can be as high as 100–200 G/mm. This excludes the use of centimeter-long cells. At the same time, owing to a small diameter of the vapor col- umn, the variation of B is several orders of magnitude lower than the absolute value of the field. In addition, a buffer gas (neon) with a pressure of ~100 Torr is added to the cell for the following reason. As was pre- viously shown [8, 9], an important condition for the formation of the EIT resonance in the Λ system with the use of cells with a micron thickness is the smallness of the frequency detuning Δ between the coupling laser and the respective atomic transition. High magnetic fields automatically result in high Δ. In this case, EIT occurs for the atoms moving in the direction of the laser radiation z at the velocity V z = 2πΔ/k, where k = 2π/λ. This leads to a decrease in the time of flight τ = L/V z (where L is the distance between the cell win- dows) and, consequently, to a fast increase in the phase decoherence rate (Γ 12 = 1/2πτ) between the two lower levels of the Λ system (a wall collision with a large probability results in the transition of the atom between the lower levels [9]). An increase in Γ 12 leads to a fast decrease in the amplitude and an increase in the width of the EIT resonance. The presence of a buffer gas (~100 Torr) greatly reduces the mean free path of the alkali atoms (down to ~1 μm). As a result, they do not reach the walls of the 30-μm cell [8]. In this paper, we report on the experimental inves- tigation of the behavior of the EIT resonance in strong magnetic fields of up to 1.7 kG with the use of the 30-μm cell filled with an atomic rubidium vapor and a buffer gas (neon). We show that the EIT resonance in the Λ system of the D 1 line of 85 Rb atoms splits in a longitudinal magnetic field into five components, whose frequency behavior depends on the frequency configuration of the probe and coupling fields and the magnitude of the magnetic field. We also show that the study of the characteristics of the EIT components in high magnetic fields can readily reveal the onset of the Splitting of the Electromagnetically Induced Transparency Resonance on 85 Rb Atoms in Strong Magnetic Fields up to the Paschen–Back Regime A. Sargsyan, R. Mirzoyan, and D. Sarkisyan* Institute for Physical Research, National Academy of Sciences of Armenia, Ashtarak-2, 0203 Armenia *e-mail: davsark@yahoo.com Received June 29, 2012 Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-μm cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the Λ system of the D 1 line of 85 Rb atoms has been formed with the use of two narrowband (~1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five compo- nents. It has been demonstrated that the frequencies of the five EIT components are either blue- or red- shifted with an increase in the magnetic field, depending on the frequency ν P of the probe laser. In has been shown that in both cases the 85 Rb atoms enter the hyperfine Paschen–Back regime in magnetic fields of >1 kG. The hyperfine Paschen–Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory. DOI: 10.1134/S0021364012170134