Todor St. Karaulanov

Reducing light-shift effects in optically-pumped gas-cell atomic frequency standards

We investigate a novel method to suppress the light-shift effect in laser-pumped passive rubidium frequency standards. The reduction of the light-shift due to additional frequency components in the pumping light is studied theoretically and compared to experimental results obtained with a frequency-modulated DBR laser diode as a pumping light source. In this way, a reduction of the light shift by a factor of 55 was successfully demonstrated. Complete cancellation of the light shift can be reached with a suitably adjusted modulation index and frequency.

Towards a simple and performing CPT based magnetometer: optimization of experimental paramaters

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.

Magnetic coherence resonance profiles in Na and K

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/cm2, 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.

Lossless formation of electromagnetically induced transparency in sodium atoms

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 Fg=2, mFg=2 or mFg=-2 can be achieved, which means complete orientation of the atoms.

Coherent Population Trapping for Continuous and Alternating Magnetic Fields Measurements

Coherent Population Trapping resonances on the D2 line of Cs are examined under the influence of continuous and alternating magnetic fields. It is shown that alternating fields as low as a fraction of μT modifies significantly the shape of the resonances, which can be used for oscillating magnetic field measurement.

Light shift reduction in atomic clocks

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.

All-optical method and device for magnetic field measurement

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 87Rb. 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.

Light shift and laser sidebands in gas-cell atomic clocks using optical pumping and coherent population trapping

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.

Coherent spectroscopy in Cs for precise magnetic field measurements

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.

Temperature dependence of coherent resonances in Na and Cs cells

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.