S. Gateva

Narrow structure in the coherent population trapping resonance in rubidium

An investigation is reported of coherent resonance in the degenerate two-level system of the (Fg = 2 --> Fe = 1) transition of the 87Rb D1 line by means of a Hanle effect configuration. In a coherent population trapping experiment, a very narrow (approximately 1-kHz) resonance superimposed upon a broader resonance (approximately 100 kHz) was observed. The dependence of the width and the amplitude of the coherent resonance on the laser power density, on additional constant magnetic fields, on the laser frequency position along the fluorescence profile, and on Rb cells with different dimensions was investigated.

Polarization-dependent sensitivity of level-crossing, coherent-population-trapping resonances to stray magnetic fields

Coherent-population-trapping resonances within the degenerate two-level system of the F=2-->F′=1 transition of the 87Rb D1 line were investigated in an uncoated Rb vapor cell by means of level-crossing-type experiments. Tuning over the two-photon resonance is achieved sweeping a magnetic field around zero value. The influence of transverse magnetic fields on the amplitude and the width of the resonances, recorded in fluorescence and absorption, were investigated in the cases of excitation with linear, circular, and elliptical laser light polarization. A theoretical analysis was performed for the case of linearly polarized excitation, the results of which are in good agreement with the experiment.

Tunable and polarization-controlled high-contrast bright and dark coherent resonances in potassium

We demonstrate high-contrast electromagnetically induced absorption (EIA) bright resonances on the D1 line of K39 with characteristics comparable to those of the electromagnetically induced transparency (EIT) dark resonances observed in the same conditions. EIA is produced by the interaction of a weak probe beam with the atomic ground state driven in a degenerate coherent superposition by either a co- or counter-propagating pump beam. We have obtained an order of magnitude increase of the EIAs contrast with respect to previous similar experiments, performed with other alkalis, without compromising its linewidth. Furthermore, we show that the magneto-optic resonances can be continuously tuned from EIT to EIA by changing the relative handedness of circular polarizations of pump and probe beams, or depending on whether they co- or counter-propagate. This opens new perspectives in the use of EIA in a broad range of physical domains and in a large wealth of potential applications in optics and photonics.

Magnetic field influence on coherent resonance in a degenerate two-level system

Coherent population trapping (CPT) resonances in the degenerate two-level system of the Fg = 2 → Fe = 1) transition of the 87Rb D1 line were investigated in an uncoated vacuum cell by means of Hanle effect configuration. CPT signals with complex shape (narrow resonance approximately 2 mG superimposed on the wide one approximately 150 mG) were observed. The influence of weak transverse magnetic fields (0-1.2 G) on the amplitude and width of the two components was measured. The observed narrow resonances are interesting for application in high resolution spectroscopy and magnetometry.

Frequency tuning peculiarities of enhanced power monomode He−Ne lasers

Experimental results are presented concerning some peculiarities of frequency tuning of single-longitudinal-mode He−Ne lasers at 632.8 nm which single-mode selection is performed by increasing the homogeneous broadening of laser transition. These include the observation of an asymmetry of tuning regions with respect to the output power maximum; a jump of lasing frequency during which output power drops; and a strong dependence of frequency tuning on gas pressure and output power. In the case of a mixture of 20Ne and 22Ne isotopes, analytical expressions for the dependence on frequency of output power, unsaturated gain and saturated gain are obtained and computed at different neon isotope concentrations, gas pressures and cavity losses. Simultaneous consideration of these dependences is proposed and used for an explanation of experimentally observed peculiarities in frequency tuning. The obtained results could be used for realization of a frequency-stabilized He−Ne laser of a few milliwatts power for the purposes of multidimensional interferometric measurements.

Light-induced atomic desorption in cells with different PDMS coatings

Light-induced atomic desorption (LIAD) is a non-thermal process in which atoms adsorbed at a surface are released under illumination. It is applied mostly to implementing optical dispensers in the cases when high atomic density at low temperature is needed – for example, for loading atomic devices as atomic magnetometers, atomic clocks, magneto-optical traps and their miniaturization. However, as the desorption depends on the atom-surface interaction, it can also be used for optical characterization and manipulation of alkali metal nanoparticles. The paper describes an experimental investigation of the shape of the transmission spectra and their dependence on the illuminating blue-light power in PDMS coated cells prepared with two different concentrations of PDMS in ether. A comparison is conducted with the LIAD effect in SC-77 coated and in uncoated cells. All measurements are performed on the Rb D2 line in vacuum. The potential is discussed for application of these dependences to analyzing the quality of the coating surface and its optimization.

Spin randomization of light-induced desorbed Rb atoms

We present the first experimental observation of atomic spin randomization of Rb atoms released by light-induced atomic desorption (LIAD). A natural mixture of Rb atoms contained in paraffin and PDMS coated glass cells is irradiated by a free-running diode laser light tuned to the Rb D2 resonance line. The transmission spectrum of the Rb vapor is thus modified and shows a strong enhancement of the hyperfine optical pumping as the light intensity is increased and the laser-frequency scanning rate is decreased. The D2 line spectra are compared for two cases: without and with illumination of the walls of the cell by a UV lamp centered around the wavelength of 404 nm. A simple theoretical model based on the solution of the rate balance equations is introduced in order to analyze the experimental results.

Narrow structure in the coherent population trapping resonances in rubidium and Rayleigh scattering

The measurement of the coherent population trapping (CPT) resonances in uncoated Rb vacuum cells has shown that the shape of the resonances is different in different cells. In some cells the resonance has a complex shape—a narrow Lorentzian structure, which is not power broadened, superimposed on the power-broadened CPT resonance. The results of the performed investigations on the fluorescence angular distribution are in agreement with the assumption that the narrow structure is a result of atom interaction with Rayleigh-scattering light. The results are interesting for indication of the vacuum cleanness of the cells and building of magnetooptical sensors.

Potential of the single-frequency CPT resonances for magnetic field measurement

Coherent population trapping (CPT) resonances on degenerate two-level system of D/sub 1/ line of /sup 87/Rb were investigated with single-frequency laser excitation in Hanle configuration. Their sensitivity to stray magnetic fields was examined for linear, elliptical, and circular laser polarization. A methodology for magnetic field (MF) measurement using the CPT resonance is proposed. The sensitivity of the system to weak magnetic fields was evaluated and a magnetic field of 3 nT was unambiguously detected.

Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating

We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D1 line of 39K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA.