1,720,979 research outputs found
Slow light and superluminality in the coherent population trapping maser Aldo Godone, Filippo Levi, and Salvatore Micalizio
No full textThe propagation of a band-limited light pulse through an atomic medium under a Λ excitation scheme is theoretically analyzed in this paper. We consider in particular the case where the light pulse is detected through the coherent microwave emission of the atomic ensemble (coherent population trapping maser). Significant differences are predicted with respect to the more usual optical detection (electromagnetically induced transparency signal) and found in agreement with the experimental results. Higher signal delays were observed in the microwave emission than in the optical signal with an equivalent group velocity of 6 m/s as well as highly superluminal propagation under a proper modulation scheme. The experiments were performed with a thermal 87Rb vapor in buffer gas
Coherent microwave emission in cesium under coherent population trapping
No full textMicrowave emission has been observed at the ground-state hyperfine transition frequency of a cesium atomic vapor driven into a nonabsorbing state by means of coherent population trapping. The coherent emission observed is due to the oscillating magnetization generated by the coherence, which is induced between the ground-state hyperfine levels when they are coupled to an excited state by means of two laser radiations via a Λ scheme. The experiments described were done in a quartz cell containing buffer gases such as neon and nitrogen, reducing the linewidth through the Dicke effect. The cell was placed inside a microwave cavity tuned at 9.2 GHz, the ground-state hyperfine frequency of cesium, and a power output of the order of 100 fW was measured in the case where nitrogen was used as the buffer gas
Pulsed optically pumped frequency standard
No full textWe reconsider the idea of a pulsed optically pumped frequency standard conceived in the early 1960s to eliminate the light-shift effect. The development of semiconductor lasers and of pulsed electronic techniques for atomic fountains and new theoretical findings allow an implementation of this idea which may lead to a frequency standard whose frequency stability is limited only by the thermal noise in the short term and by the temperature drift in the long term. We shall also show both theoretically and experimentally the possibility of doubling the atomic quality factor with respect to the classical Ramsey technique approach
Rabi resonances in the Λ excitation scheme
No full textWe consider the interaction of a three-level system with phase-modulated resonant fields in the Λ excitation scheme. We treat theoretically the case of a sinusoidal phase modulation, a phase step perturbation, and a stochastic phase modulation. The appearance of a Rabi resonance both in the spectrum of the optical transmitted signal (electromagnetically induced transparency) and in the spectrum of the microwave emission (coherent population trapping maser) is considered in detail. All the theoretical results are compared with the analogous ones reported for the two-level system and with our experimental observations obtained for the case of rubidium in a buffer gas
A Conversation with Dr. Aldo Godone, Scientific Coordinator of the Istituto Nazionale di Ricerca Metrologica (INRIM) in Italy
No full textCoherent population trapping in cesium: Dark lines and coherent microwave emission
No full textThe phenomenon of coherent population trapping in alkali-metal atoms is analyzed by means of a perturbation approach. Closed form transparent solutions are obtained for the coherences existing within the system and the populations of the ground levels and of the excited state. The presence of dark lines and coherent microwave emission from the ground state are made explicit. Experimental results that confirm the theoretical calculations are reported for the case of cesium in a buffer gas. Conclusions are drawn in connection with the application of coherent population trapping to the field of atomic frequency standards
Ramsey-fringe shape in an alkali-metal vapor cell with buffer gas
No full textIn this paper we describe a few phenomena that may affect the linewidth and/or the line shape of Ramsey
fringes observed in an alkali-metal vapor cell with buffer gas. Experiments are performed on a vapor-cell–
microwave-cavity arrangement in which 87Rb atoms successively experience laser pumping preparation (through
aD2 line), microwave interrogation with a couple of coherent pulses, and clock signal detection by means of laser
absorption. We show that the linewidth of the Ramsey central fringe is influenced by the Rabi pattern produced
by a single microwave pulse. Moreover, cycle memory and atomic density effects can modify the shape of the
Ramsey central fringe from the common sinusoidal behavior. A simple three-level model well reproduces the
experimental observations
Theory of the coherent population trapping maser: A strong-field self-consistent approach
No full textThe phenomenon of coherent microwave stimulated emission in a cavity is analyzed for the case of alkali atoms such as Cs and Rb under coherent population trapping (CPT) in a Λ scheme. The calculations are made in transient and in continuous operation within the framework of a three level model. The coupling of the atoms to the microwave field generated inside the cavity by the atomic ensemble, is fully taken into account; it introduces radiation damping and an imbalance in the populations of the ground-state hyperfine levels, decreasing the intrinsic symmetry of the Λ scheme. The effect leads also to a broadening and to a frequency shift of the microwave emission profile. A comparison is made with the optically pumped alkali atom maser, allowing a deeper understanding of the CPT stimulated emission phenomenon
Spin-exchange frequency shift in alkali-metal-vapor cell frequency standards
No full textIn this paper we calculate the effect of spin-exchange collisions in alkali-metal vapors. In the framework of the high-energy approximation, we evaluate the spin-exchange cross sections related to the line broadening and to the frequency shift of the ground state hyperfine transition. We do the calculation for the four isotopes, 23Na, 39K, 87Rb, and 133Cs. The results are used in particular to evaluate the spin-exchange frequency shift in Rb vapor cell frequency standards used in many applications. It turns out that, due to possible fluctuations in the atomic density, spin exchange may affect significantly the medium and long term frequency stability of the frequency standard
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