Influence of the finite linewidth of the laser radiation spectrum on the shape of the coherent population trapping reson
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Influence of the Finite Linewidth of the Laser Radiation Spectrum on the Shape of the Coherent Population Trapping Resonance Line in an Optically Dense Medium with a Buffer Gas K. A. Barantsev*, E. N. Popov, and A. N. Litvinov** Peter the Great St. Petersburg Polytechnic University, St. Petersburg, 195251 Russia *e-mail: [email protected] **e-mail: [email protected] Received April 7, 2015
Abstract—The theory of coherent population trapping resonance is developed for the finite linewidth of the laser radiation spectrum in an optically dense medium of Λ atoms in a cell with a buffer gas. Equations are derived for the atomic density matrix and laser emission spectrum transfer in a cell with working and buffer gases at a finite temperature. The dependence of the quality factor of coherent population trapping resonance on the linewidth of the laser radiation spectrum is studied by measuring transmitted radiation and fluorescence signals. DOI: 10.1134/S1063776115110011
1. INTRODUCTION The interaction of multifrequency laser radiation with quantum systems can result in the appearance of new nonlinear optical effects. Among these effects are coherent population trapping (CPT) [1–4] and the related electromagnetically induced transparency (EIT) [5, 6]. The CPT (EIT) effect in a simple nondegenerate Λ system is the appearance of quantum interference between two-frequency laser excitation channels. This leads to the absence of absorption in the given medium in a certain frequency region, resulting in the appearance of a transparency window in the medium. The width of this transparency window at sufficiently low laser radiation intensities is determined by the decay rate of the radio frequency coherence, which in alkali atoms is five orders of magnitude smaller than the decay rate of optical coherences. Such a feature allows the use of this transparency window for the development of new-generation quantum frequency standards [7, 8], optical magnetometers [9, 10], high-resolution spectroscopic instruments [11, 12], devices for data recording and storage [13, 14], etc. As mentioned above, CPT has found an important application in the field of new-generation quantum frequency standards (QFSs). A distinct feature and advantage of CPT over traditional QFSs based on double radio frequency resonance [15–17] is the absence of a microwave resonator, allowing the reduction in device size and energy consumption.
The CPT effect in cells has been studied in many works. One particular directions is the study of the CPT resonance shape in rubidium atoms in cells with a buffer gas for continuous radiation. Thus, the authors of [18] considered theoretically for the first time the possibility of the appearance of pseudoresonance in the field of copropagating waves. This effect was experimentally studied in [19, 20]. The development of these works with the aim of using pseudoresonance as a reference for small QFSs is demonstrated in [21, 22]. The optical pumping of cesium atoms in orthogonal laser fields and CPT in th
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