Emilia Alipieva

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.

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.

Coherent population trapping for magnetic field measurements

The purpose of this communication is to summarize and compare the results obtained under the project New all-optical systems and methods for magnetic and electromagnetic field measurement, financed by EC (contract G6RD-CT-2001-000642). The main aim of the project is investigation of the potential of different approaches based on the effect of Coherent Population Trapping (CPT) for magnetic field measurement. The investigated approaches are: (i) CPT prepared by coupling pairs of non-degenerate Zeeman sublevels belonging to the two ground-state hyperfine components of alkali atoms by means of polychromatic laser field; (ii) CPT prepared by coupling degenerate Zeeman sublevels belonging to a single ground-state hyperfine component of alkali atoms by means of single-frequency laser field of appropriate polarization at zero magnetic field (MF); and (iii) polychromatic laser field coupls pairs of non-degenerate Zeeman sublevels belonging to a single ground-state hyperfine level of alkali atoms.

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.

Coherent population trapping resonance on degenerate two-level system for magnetic field measurement

Coherent population trapping (CPT) resonances on 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 level-crossing type experiments-sweeping a magnetic field around zero value and using a single laser beam. The two-photon resonance manifests itself as fluorescence canceling when the system of levels is degenerate (at zero point of magnetic field). The influence of weak transverse magnetic fields on the amplitude and width of the resonance was investigated. The CPT resonances were observed with linear, circular and elliptical polarized laser light. Transverse magnetic field widens the resonances obtained by linear and circular polarization but splits the resonance created by slightly elliptically polarized laser light. The dependence of this splitting on the elliptical ratio and experimental geometry were investigated. Due to its narrow width and sensitivity to low magnetic fields (< 1 G) this resonance is very promising for small magnetic field measurement.

Magneto-optical resonance of the polarized fluorescence in a paraffin-coated 87 Rb vacuum cell

In this work we investigate the magneto-optical resonance on 87Rb D1 line. In two-level degenerated system this resonance is due to the interference between the Zeeman sub-levels, created by interaction of resonance linear polarized laser beam with the atoms. The observed signal is detected by sweeping magnetic field B around its zero value. This phenomenon is also known as a Coherent Population Trapping (CPT) in Hanle-configuration. In a coated vacuum cell the fluorescence signal has a complex form, because the anti-relaxation coating preserves the created coherence, having different relaxation rates. The ground state coherence is transmitted by the laser field to the upper level; thereby polarization moments with different rank contribute to the fluorescence. The manifestation of the different polarization moments in the observed signal depends on the geometry of the experiment – direction of observation, plane of the laser polarization, polarization of the registered light. The resonances obtained in the fluorescence having different polarization are compared in order to clear up what are the contributions to the fluorescent signal from the polarization moments with different rank. The experiment is performed on the D1 87Rb line, F=2→ F=1 transition in a paraffin-coated cell. The magneto-optical resonances, detected in two orthogonal polarizations are measured. Numerical calculations with parameters, close to the experimental ones are performed by using a program, which is based on the irreducible tensor operator formalism. The results of the modelling are compared with the measured ones at different experimental conditions.

Manifestation of high-rank polarization moments in the fluorescence CPT resonance

Coherent Population Trapping (CPT) resonance obtained with linearly polarized laser beam through magnetic field sweep (Hanle configuration) was investigated in 87Rb D1 line. Influence of the coherence due to high-rank polarization moment (hexadecapole moment), created in the medium, on the CPT resonance shape was calculated and experimentally detected in fluorescence. It was observed as an inverted structure at a high power of excitation. To distinguish resonances due to coherence between Zeeman sub-levels with ΔmF=2 from that with ΔmF=4, the Larmour frequency ωLmodulated by applying an a.c. magnetic field (a.c. MF). Resonance signal at frequency corresponding to 4ωL observed in a fluorescence, and after lock-in on the frequency corresponding to frequency difference between sub-levels ΔmF=4.

Power dependence of the coherent population trapping resonances at different registration

The investigation of the coherent population trapping (CPT) resonance on the degenerate two-level system of the (Fg=2→Fe=1) transition of the 87Rb D1 line by means of Hanle effect configuration in an uncoated vacuum cell (Opt. Lett. 28, 1817, 2003), has shown that the measured in fluorescence resonance has a complex shape: a very narrow (about 1mG) resonance superimposed on a broader one (about few tens mG). In this work the narrow and wide CPT resonances are registered in fluorescence, transmitted light and Faraday rotation. The dependence of the CPT resonances structures width and amplitude are measured at different laser power densities when the registration was in fluorescence and transmission. While the narrow resonance width doesnt change in the limits of the accuracy of our measurements, the wide resonance width dependence is complex and it is different in fluorescence and transmission. The origin of the observed dependencies and the differences between CPT signals observed in fluorescence and transmission are discussed.