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Optics and Spectroscopy

Electromagnetically induced transparency in a molecular gas

Н. Н. Рубцова

Published Jul 1, 2001• 8 citations
Publisher

Abstract

The dynamic Stark effect on the as Q (5,4) transition of the 0 → 1 vibrational band of the ν 2 mode of ammonia 15 NH 3 was studied by the method of copropagating waves of radiation of two 13 CO 2 lasers operating at the R (18) I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm 2 , and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of 15 NH 3 . When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.

DOI
10.1134/1.1388324

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Physical Review A•Apr 11, 2003•28 citations
The dynamic Stark effect on the as Q (5,4) transition of the 0 → 1 vibrational band of the ν 2 mode of ammonia 15 NH 3 was studied by the method of copropagating waves of radiation of two 13 CO 2 lasers operating at the R (18) I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm 2 , and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of 15 NH 3 . When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.
Free polarization decay and photon echo were studied experimentally in polar gas 13CH3F at the transition R(4,3) of vibrational mode 0 yields 1 (nu) 3 by Stark switching of molecular levels under irradiation by CW CO2 laser at 9P(32) line. Application of 4.5 mcs pulse to the Stark electrodes inside the gas cell allows to detect the free polarization decay signal, combined with the optical nutation. The sign of the signal corresponds to the increase of absorption in the limit of low intensity (not over 0.01 W/cm2) saturating radiation. Exciting intensity growth till the level of 6.0 W/cm2 implies decrease of signal absolute value, till the change of its sign, while the oscillation of the free polarization decay signal reveals remarkable frequency shift. Such behavior is attributed to the combined action of the dynamic Stark effect of CW radiation field and the levels splitting by the Stark voltage. Two shorter (of about 0.1 and 0.2 mcs) Stark pulses, applied to the gas, generate the photon echo signals detected by the same heterodyne technique. The study of the variations of photon echo parameters versus exciting radiation intensity is in progress.
We report the experimental observation of electromagnetically induced transparency (EIT) in an inhomogeneously broadened V-type Na2{}_{2}2​ molecular system. The experiment is performed with both co- and counterpropagating arrangements for the propagation directions of the coupling and probe laser beams. In our theoretical model we employ the density matrix formalism, as well as perturbative methods for obtaining the probe field absorption profile for both open and closed systems. Simulations of the experimental data show excellent agreement with the predictions derived from the basic theory. Our fluorescent intensity measurements show that, in the copropagating configuration, the EIT plus saturation window depth is about 9595%95, while under similar conditions in the counterpropagating geometry we observed 4040%40--4545%45 reduction in the fluorescence signal around the line center. To separate the two simultaneously occurring mechanisms in a V-type system (i.e., EIT and saturation) that are induced by the coupling field, we have carried out theoretical calculations which show that, in the copropagating case, a significant fraction of the depth of the dip is due to the coherent effect of EIT. When the coupling and probe beams are in the counterpropagating configuration, the dip is mostly due to saturation effects alone.
The conclusions of a theoretical study of the dependence of the characteristics of the phenomenon of electromagnetically induced transparency on the pulse intensity of the input probe radiation under elliptical polarization of laser fields have been reported. The analysis has been carried out for the Ʌ-scheme of inhomogeneously broadened quantum transitions between the levels 3P0{}^{3}{{P}_{0}}3P0​ , 3P10{}^{3}P_{1}^{0}3P10​ , and 3P2{}^{3}{{P}_{2}}3P2​ of the 208Pb isotope. The cases of resonance, i.e., the coincidence of the frequencies of the probe and control fields with the central frequencies of the corresponding quantum transitions, and quasi-resonance, when such a coincidence occurs only up to the line width of the corresponding quantum transition, have been considered. It has been shown that in these cases there is a tendency for the input probe radiation to split into pulses with different polarization characteristics. If the input probe radiation is weak enough, these pulses have constant polarization characteristics and are normal mode pulses. In the case of a higher power of the input probe radiation, the pulses into which it splits in the medium are not normal mode pulses, but their polarization characteristics fluctuate near the values inherent in normal modes. At the same time, the phase modulation of the probe field is present at all stages of its propagation in the medium. It has been shown that the transparency of the medium for the probe field decreases with increasing intensity of the input probe radiation. However, it is sufficiently large if the polarization characteristics of the input probe radiation coincide with those for the normal mode, the major axis of the polarization ellipse of which is parallel to the major axis of the control field polarization ellipse.
Abstract We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87 Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D 2 line of 87 Rb in a Λ -type configuration. With a 5 Torr N 2 buffer gas in the thermal 2 cm vapor cell, the state 5 2 P 3 / 2 has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87 Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.
The interaction of a two-level system with a strong standing wave is examined by the probe field resonant to the adjacent transition in the $\ensuremath{\Lambda}$ configuration of Ar II. The known peak of electromagnetically induced transparency is observed in the absorption spectrum at the detuning of the probe field proportional to the detuning of the strong field. Along with it, the different structure has been found at the line center, independently of the strong-field frequency. The calculations clarify that the central structure is induced by the higher-order spatial harmonics of the atomic coherence induced at the probe transition. The effect results in steep frequency dependence of the refractive index at the line center.