In this communication we present our results related to examination of Coherent Population Trapping resonance profile
on the D<sub>1</sub> line of <sup>87</sup>Rb when coupling two ground-state Zeeman sublevels belonging to different hyperfine ground-state
levels to a common excited-state one. For this, two coherent laser fields with frequency difference of about 6.8 GHz are
used. The resonance is observed as a narrow dip in the fluorescence in dependence on the modulation frequency (f<sub>m</sub>) of
the laser light, centered at 2f<sub>m</sub> = &Dgr;<i>v</i><sub>hf</sub> , where &Dgr;<i>v</i><sub>hf</sub> is the frequency difference between the ground-state hyperfine levels
of Rb. The resonance observation and its splitting in 7 components have been demonstrated under influence of nonshielded
laboratory magnetic field (MF). It has been shown that different components are with different sensitivity to the
MF gradients that is in agreement with the performed estimations.
Magnetic coherence resonance profiles, obtained at magetic field B = O in Hanle configuration were examined for Na and K atoms in different cells: evacuated glass cells and buffered, coated and uncoated. At low laser power for all cells the shape of the resonancees is Lorentzian. At power higher than about 100 mW/cm<sup>2</sup>, some narrowing around the resonance peak is observed for the Na buffered cell, while for the vacuum one the resonance shape is even more complex. Theoretical explanation is proposed for the complex resonance shape evidenced in the vacuum cells. Large resonance contrast in the K absorption at B = 0 is observed, attributed to the low rate of hyperfine optical pumping in K. The detailed investigation of the resonance profiles and contrast is of very high importance for their application.
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.
A simple set-up for observation of CPT effect at single hyperfine ground state excitation has been examined for application in measurements of non-vanishing magnetic fields. The CPT is prepared using low-frequency modulated (in the kHz range) diode laser. Magnetic field measurements down to 500 pT sensitivity and reproducibility were obtained for integration time of 30 ms. One of the important characteristics of the proposed methodology is a proper Cs excitation in order to overcome effectively the huperfine optical pumping effefct. This is possible working in narrow ranges of laser beam intensity, buffer gas pressures and Cs vapor densities. The best conditions have been experimentally determined and discussed.
In this paper we propose a simple method for eliminating the population losses of MC resonances by involving all atoms of the Na ground state in the formation of the narrow coherent resonances observed in the fluorescence when scanning around zero value the applied magnetic field. As a result, dark resonances with a contrast up to 100% have been observed. Results are obtained in two different experimental configurations: using laser excitation of linear and circular polarization, leading to different population redistribution among Zeeman and hf levels. Theoretical analysis of the results is also presented. It is shown that at certain conditions complete optical pumping of atoms to levels F<sub>g</sub>=2, m<sub>Fg</sub>=2 or m<sub>Fg</sub>=-2 can be achieved, which means complete orientation of the atoms.
In the present communication we report on the investigation of the effect of elliptically polarized laser light exciting the F<sub>g</sub>=3 Cs D<sub>2</sub> absorption line. Coherent resonances in Cs have been studied, obtained in Hanle configuration by scanning of magnetic field parallel to the light propagation direction. The resonances were investigated depending on the polarization of the irradiating light field. It has been observed that for linear polarization dark resonances in the fluorescence are registered, while for circularly polarized light, bright resonances are obtained, probably due to stray orthogonal magnetic field. For elliptical polarization a narrow peak appears superimposed on a broader dip. Theoretical description has been made, which shows that at elliptical polarization and orthogonal magnetic field in the case of weak light fields, a single peak in the excited state population is observed, while strong fields lead to the splitting of this peak into two peaks. The presence of both weak and strong light fields, probably due to reflection of the light beam on the cell walls, could lead to the experimentally observed fluorescence behaviour.
Investigation on coherent population trapping and electromagnetic induced absorption effects has been made in Cs vapors. A detailed analysis of degenerate and non-degenerate cases is reported. Possible application to precise magnetic field measurements is discussed and preliminary results described.
Diode laser system with frequency modulation in the GHz region has been built. The two first sidebands of the frequency modulated laser spectrum are used for preparation of CPT resonances in <sup>87</sup>Rb. The CPT resonance splitting in magnetic field is examined by registering the fluorescence or its first derivative in dependence on the modulation frequency. Measuring the frequency difference between the CPT resonances, the value of the magnetic field is determined.
In this paper we present a detailed description of a method for reduction of the light shift in laser-pumped gas-cell atomic clocks. The method consists in using a multi-frequency optical pumping obtained through frequency modulation of the laser spectrum with precisely controllable parameters. Experimental evidence of a strong reduction of the frequency dependence of the LS in an optical pumping Rb gas-cell clock is demonstrated in a large frequency interval, which is in a very good agreement with the numerical estimations reported.
The problem for phase matching (PM) of several nonlinear processes is one of the main in nonlinear optics and in optical switching technology. We propose a novel scheme for dual channel third harmonic (TH) generation using a single two dimensional nonlinear photonic crystal (2DNPC). The proposed interaction at low input intensities is four times more efficient than the conventional schemes.
Temperature dependences of coherent resonances in Na and Cs atoms prepared by two coherent laser frequencies or two polarizations of single frequency laser field are presented. It is shown that the temperature dependence of the amplitude or contrast of the resonances in most cases exhibits a maximum. For both types of coherent resonances, a reason for the contrast reduction at higher temperature is the increased absorption of the laser light along the gas cell due to the optical thickness of the medium. Spin-exchange collisions lead to resonance contrast reduction more effectively in a cell with pure alkali atoms.
In the present communication we report on the study of the locking position of the frequency of a diode laser on different external parameters like the temperature of the reference cell, external magnetic field and the intensity of the pump and probe beams preparing saturation absorption. This study is important in view of applications of frequency stabilized diode lasers for atomic clocks istead of discharge lamps.
Theoretical and experimental investigation of the light shift in optical pumping and coherent population trapping based gas-cell atomic frequency standards is reported. A possibilty for realization of a minimial (possibly zero) light shift configuration is discussed.